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Michael Westerman - One of the best experts on this subject based on the ideXlab platform.
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A Phylogeny and Timescale for Marsupial Evolution Based on Sequences for Five Nuclear Genes
Journal of Mammalian Evolution, 2008Co-Authors: Robert W Meredith, Judd A. Case, Michael Westerman, Mark S SpringerAbstract:Even though Marsupials are taxonomically less diverse than placentals, they exhibit comparable morphological and ecological diversity. However, much of their fossil record is thought to be missing, particularly for the Australasian groups. The more than 330 living species of Marsupials are grouped into three American (Didelphimorphia, Microbiotheria, and Paucituberculata) and four Australasian (Dasyuromorphia, Diprotodontia, Notoryctemorphia, and Peramelemorphia) orders. Interordinal relationships have been investigated using a wide range of methods that have often yielded contradictory results. Much of the controversy has focused on the placement of Dromiciops gliroides (Microbiotheria). Studies either support a sister-taxon relationship to a monophyletic Australasian clade or a nested position within the Australasian radiation. Familial relationships within the Diprotodontia have also proved difficult to resolve. Here, we examine higher-level marsupial relationships using a nuclear multigene molecular data set representing all living orders. Protein-coding portions of ApoB, BRCA1, IRBP, Rag1, and vWF were analyzed using maximum parsimony, maximum likelihood, and Bayesian methods. Two different Bayesian relaxed molecular clock methods were employed to construct a timescale for marsupial evolution and estimate the unrepresented basal branch length (UBBL). Maximum likelihood and Bayesian results suggest that the root of the marsupial tree is between Didelphimorphia and all other Marsupials. All methods provide strong support for the monophyly of Australidelphia. Within Australidelphia, Dromiciops is the sister-taxon to a monophyletic Australasian clade. Within the Australasian clade, Diprotodontia is the sister taxon to a Notoryctemorphia + Dasyuromorphia + Peramelemorphia clade. Within the Diprotodontia, Vombatiformes (wombat + koala) is the sister taxon to a paraphyletic possum group (Phalangeriformes) with kangaroos nested inside. Molecular dating analyses suggest Late Cretaceous/Paleocene dates for all interordinal divergences. All intraordinal divergences were placed in the mid to late Cenozoic except for the deepest splits within the Diprotodontia. Our UBBL estimates of the marsupial fossil record indicate that the South American record is approximately as complete as the Australasian record.
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Nuclear gene sequences provide evidence for the monophyly of australidelphian Marsupials
Molecular Phylogenetics and Evolution, 2003Co-Authors: Heather Amrine-madsen, Mark Scally, Michael Westerman, Carey Krajewski, Michael J Stanhope, Mark S SpringerAbstract:Abstract Relationships among the seven extant orders of Marsupials remain poorly understood. Most classifications recognize a fundamental split between Ameridelphia, which contains the American orders Didelphimorphia and Paucituberculata, and Australidelphia, which contains four Australasian orders (Dasyuromorphia, Diprotodontia, Notoryctemorphia, and Peramelina) and the South American order Microbiotheria, represented by Dromiciops gliroides. Ameridelphia and Australidelphia are each supported by key morphological characters with dichotomous character states. To date, molecular studies indexing all marsupial orders have reported inconclusive results. However, several studies have suggested that Dromiciops is nested within Australidelphia. This result has important implications for understanding the biogeographic history of living Marsupials. To address questions in higher-level marsupial systematics, we sequenced portions of five nuclear genes (Apolipoprotein B gene; Breast and Ovarian cancer susceptibility gene 1; Recombination activating gene 1; Interphotoreceptor retinoid binding protein gene; and von Willebrand factor gene) for representatives of all orders of Marsupials, as well as placental outgroups. The resulting 6.4 kb concatenation was analyzed using maximum parsimony, distance methods, maximum likelihood, and Bayesian methods. Kishino and Hasegawa (1989) tests were used to examine a priori hypotheses. All analyses provided robust support for the monophyly of Australidelphia (bootstrap support=99–100%; posterior probability=1.00). Ameridelphia received much lower support, although this clade was not rejected in statistical tests. Within Diprotodontia, both Vombatiformes and Phalangeriformes were supported at the 100% bootstrap level and with posterior probabilities of 1.00.
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Marsupial Genetics and Genomics - Marsupial genetics and genomics
Trends in Genetics, 2002Co-Authors: Jennifer A. Marshall Graves, Michael WestermanAbstract:Marsupials, the 'other' mammals, are found only in Australasia and the Americas. They are quite different from eutherian ('placental') mammals, as well they might be after 130 million years of separate evolution. They display a unique pattern of mammalian organization and development that is reflected by differences in their genomes. Here, we introduce Marsupials as alternative (but not inferior!) mammals and summarize the state of knowledge of marsupial relationships, marsupial chromosomes, maps, genes and genetic regulatory systems. We shamelessly present the case for a Kangaroo Genome Project.
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An Analysis of Marsupial Interordinal Relationships Based on 12S rRNA, tRNA Valine, 16S rRNA, and Cytochrome b Sequences
Journal of Mammalian Evolution, 1999Co-Authors: Angela Burk, John R. Kavanagh, Michael Westerman, Mark S SpringerAbstract:The basal split among living Marsupials is traditionally placed between the cohorts Ameridelphiaand Australidelphia. Ameridelphia includes all American forms excepting the South American Dramicuipx gliroidex (Order Microbiotheria). Australidelphia includes all Australasian taxaplus Dromiciops glinmles . DNA data support Eometatheria Dromiciaps + Diprotodontia +Dasyuromorphia + Notoryctemorphia) but do not resolve the position of bandicoots, whetherwith other australidelphians or with ameridelphians. Also, the most robust molecular trees (DNAhybridization, multigene studies) exhibit minimal branch subdivision and raise the possibility ofartit'actual associations owing to long branch attraction. We analyzed data sets that consistedof complete sequences tor four niitochondrial genes (cytochrome b , 12S rRNA, tRNA valine,16S rRNA). One data set included 14 marsupial taxa. A second data set included 14 Marsupialsas well as outgroup sequences (one monolreme; 20 placentals). Phylogenetic analyses includedparsimony, minimum evolution, maximum likelihood, and quartet puzzling. When phylogeneticanalyses were restricted to just the marsupial sequences, there was 75 to 96% boostrap supportfor the separation of Ameridelphia versus Australidelphia. This suggests that either one orboth of these groups are monophyletic. Also, there was 71 to 98% bootstrap support for theseparation of Eometatheria versus Ameridelphia + Peramelina. Nonmonophyly of several a prioriclades was accepted by at least some statistical tests including the following: Diprotodontia+ Peramelina, Notoryctemorphia + Peramelina, Diprotodonlia + Notoryctemorphia, and themonophyly of Australasian Marsupials. With the inclusion of outgroup sequences, there wasreduced bootstrap support for associations among marsupial orders and statistical tests failed toreject all interordinal associations that were tested.
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Evolution of the Monotremes: Phylogenetic Relationship to Marsupials and Eutherians, and Estimation of Divergence Dates Based on α-Lactalbumin Amino Acid Sequences
Journal of Mammalian Evolution, 1998Co-Authors: Michael Messer, Anthony S. Weiss, Denis C. Shaw, Michael WestermanAbstract:The amino acid sequences of the α-lactalbumins of the echidna, Tachyglossus aculeatus , and the platypus, Ornithorhynchus anatinus , were compared with each other and with those of 13 eutherian and 3 marsupial species. Phylogenetic parsimony analyses, in which selected mammalian lysozymes were used as outgroups, yielded trees whose consensus indicated that the two monotremes are sister taxa to Marsupials and eutherians and that the latter two clades are each other's closest relatives. The data do not support the notion of a Marsupionta (monotreme–marsupial) clade. Pairwise comparison between the α-lactalbumins yielded maximum-likelihood distances from which divergence dates were estimated on the basis of three calibration points. The distance data support the view that the echidna and platypus lineages diverged from their last common ancestor at least 50 to 57 Ma (million years ago) and that monotremes diverged from Marsupials and eutherian mammals about 163 to 186 Ma.
Mark S Springer - One of the best experts on this subject based on the ideXlab platform.
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A Phylogeny and Timescale for Marsupial Evolution Based on Sequences for Five Nuclear Genes
Journal of Mammalian Evolution, 2008Co-Authors: Robert W Meredith, Judd A. Case, Michael Westerman, Mark S SpringerAbstract:Even though Marsupials are taxonomically less diverse than placentals, they exhibit comparable morphological and ecological diversity. However, much of their fossil record is thought to be missing, particularly for the Australasian groups. The more than 330 living species of Marsupials are grouped into three American (Didelphimorphia, Microbiotheria, and Paucituberculata) and four Australasian (Dasyuromorphia, Diprotodontia, Notoryctemorphia, and Peramelemorphia) orders. Interordinal relationships have been investigated using a wide range of methods that have often yielded contradictory results. Much of the controversy has focused on the placement of Dromiciops gliroides (Microbiotheria). Studies either support a sister-taxon relationship to a monophyletic Australasian clade or a nested position within the Australasian radiation. Familial relationships within the Diprotodontia have also proved difficult to resolve. Here, we examine higher-level marsupial relationships using a nuclear multigene molecular data set representing all living orders. Protein-coding portions of ApoB, BRCA1, IRBP, Rag1, and vWF were analyzed using maximum parsimony, maximum likelihood, and Bayesian methods. Two different Bayesian relaxed molecular clock methods were employed to construct a timescale for marsupial evolution and estimate the unrepresented basal branch length (UBBL). Maximum likelihood and Bayesian results suggest that the root of the marsupial tree is between Didelphimorphia and all other Marsupials. All methods provide strong support for the monophyly of Australidelphia. Within Australidelphia, Dromiciops is the sister-taxon to a monophyletic Australasian clade. Within the Australasian clade, Diprotodontia is the sister taxon to a Notoryctemorphia + Dasyuromorphia + Peramelemorphia clade. Within the Diprotodontia, Vombatiformes (wombat + koala) is the sister taxon to a paraphyletic possum group (Phalangeriformes) with kangaroos nested inside. Molecular dating analyses suggest Late Cretaceous/Paleocene dates for all interordinal divergences. All intraordinal divergences were placed in the mid to late Cenozoic except for the deepest splits within the Diprotodontia. Our UBBL estimates of the marsupial fossil record indicate that the South American record is approximately as complete as the Australasian record.
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Nuclear gene sequences provide evidence for the monophyly of australidelphian Marsupials
Molecular Phylogenetics and Evolution, 2003Co-Authors: Heather Amrine-madsen, Mark Scally, Michael Westerman, Carey Krajewski, Michael J Stanhope, Mark S SpringerAbstract:Abstract Relationships among the seven extant orders of Marsupials remain poorly understood. Most classifications recognize a fundamental split between Ameridelphia, which contains the American orders Didelphimorphia and Paucituberculata, and Australidelphia, which contains four Australasian orders (Dasyuromorphia, Diprotodontia, Notoryctemorphia, and Peramelina) and the South American order Microbiotheria, represented by Dromiciops gliroides. Ameridelphia and Australidelphia are each supported by key morphological characters with dichotomous character states. To date, molecular studies indexing all marsupial orders have reported inconclusive results. However, several studies have suggested that Dromiciops is nested within Australidelphia. This result has important implications for understanding the biogeographic history of living Marsupials. To address questions in higher-level marsupial systematics, we sequenced portions of five nuclear genes (Apolipoprotein B gene; Breast and Ovarian cancer susceptibility gene 1; Recombination activating gene 1; Interphotoreceptor retinoid binding protein gene; and von Willebrand factor gene) for representatives of all orders of Marsupials, as well as placental outgroups. The resulting 6.4 kb concatenation was analyzed using maximum parsimony, distance methods, maximum likelihood, and Bayesian methods. Kishino and Hasegawa (1989) tests were used to examine a priori hypotheses. All analyses provided robust support for the monophyly of Australidelphia (bootstrap support=99–100%; posterior probability=1.00). Ameridelphia received much lower support, although this clade was not rejected in statistical tests. Within Diprotodontia, both Vombatiformes and Phalangeriformes were supported at the 100% bootstrap level and with posterior probabilities of 1.00.
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An Analysis of Marsupial Interordinal Relationships Based on 12S rRNA, tRNA Valine, 16S rRNA, and Cytochrome b Sequences
Journal of Mammalian Evolution, 1999Co-Authors: Angela Burk, John R. Kavanagh, Michael Westerman, Mark S SpringerAbstract:The basal split among living Marsupials is traditionally placed between the cohorts Ameridelphiaand Australidelphia. Ameridelphia includes all American forms excepting the South American Dramicuipx gliroidex (Order Microbiotheria). Australidelphia includes all Australasian taxaplus Dromiciops glinmles . DNA data support Eometatheria Dromiciaps + Diprotodontia +Dasyuromorphia + Notoryctemorphia) but do not resolve the position of bandicoots, whetherwith other australidelphians or with ameridelphians. Also, the most robust molecular trees (DNAhybridization, multigene studies) exhibit minimal branch subdivision and raise the possibility ofartit'actual associations owing to long branch attraction. We analyzed data sets that consistedof complete sequences tor four niitochondrial genes (cytochrome b , 12S rRNA, tRNA valine,16S rRNA). One data set included 14 marsupial taxa. A second data set included 14 Marsupialsas well as outgroup sequences (one monolreme; 20 placentals). Phylogenetic analyses includedparsimony, minimum evolution, maximum likelihood, and quartet puzzling. When phylogeneticanalyses were restricted to just the marsupial sequences, there was 75 to 96% boostrap supportfor the separation of Ameridelphia versus Australidelphia. This suggests that either one orboth of these groups are monophyletic. Also, there was 71 to 98% bootstrap support for theseparation of Eometatheria versus Ameridelphia + Peramelina. Nonmonophyly of several a prioriclades was accepted by at least some statistical tests including the following: Diprotodontia+ Peramelina, Notoryctemorphia + Peramelina, Diprotodonlia + Notoryctemorphia, and themonophyly of Australasian Marsupials. With the inclusion of outgroup sequences, there wasreduced bootstrap support for associations among marsupial orders and statistical tests failed toreject all interordinal associations that were tested.
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dna hybridisation studies of Marsupials and their implications for metatherian classification
Australian Journal of Zoology, 1997Co-Authors: John A W Kirsch, Mark S Springer, Francoisjoseph LapointeAbstract:We review past DNA-hybridisation studies of Marsupials and present a reanalysis of the data, utilising results from our and additional studies to formulate and rationalise a new classification of Marsupialia. In the reanalysis, 13 individual DNA-hybridisation matrices, many lacking some pairwise comparisons, were sutured in stages to provide the basis for generating a tree of 101 Marsupials plus an outgroup eutherian; a fourteenth matrix provided data for a tree including eight additional eutherians and a monotreme. Validation was achieved by jackknifing on taxa for each matrix as well as on tables combining two or more matrices generated during assembly of the 102-taxon data set. The results are consistent with most conclusions from the individual studies and dramatise the unevenness of hierarchical levels in current classifications of Marsupials. In particular, the affinities of the American marsupial Dromiciops gliroides with, and the distinctness of marsupial bandicoots from, Australasian metatherians are reaffirmed, while opossums are shown to be as internally divergent as are most members of the order Diprotodontia. Calibration of the 102-taxon tree and dating of the major dichotomies suggest that no extant marsupial lineage originated before the latest Cretaceous, and that all of them together with most South American and all Australasian fossils should be recognised as a monophyletic group contrasting with a largely Laurasian (if possibly paraphyletic) taxon. These inferences, together with the details of the phylogeny, mandate that the misleading ‘Australian’ v. ‘American’ distinction be abandoned, even as a geographic convenience.
Marcelo R. Sánchez-villagra - One of the best experts on this subject based on the ideXlab platform.
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Ontogeny and phylogeny of the mammalian chondrocranium: the cupula nasi anterior and associated structures of the anterior head region
Zoological Letters, 2018Co-Authors: Evelyn Hüppi, Marcelo R. Sánchez-villagra, Athanasia C. Tzika, Ingmar WerneburgAbstract:Background The study of chondrocrania has a long tradition with a focus on single specimens and stages. It revealed great interspecific diversity and a notion of intraspecific variation. As an embryonic structure, the chondrocranium is subject to major changes in ontogeny with resorption and ossification of different cartilaginous structures. The cupula nasi anterior is the anteriormost portion of the cartilaginous nasal capsule and is expected to mirror much of the animal's life history and lifestyle. Its diversity in mammals is reflected in the external nasal anatomy of newborns. Marsupials and placentals show marked differences, likely related to breathing and suckling behavior. Results We examined histological sections of five marsupial and three placentals species and traced the development of the cupula nasi anterior and the anterior nasal capsule. We found ontogenetic variation for nearly 50% of the 43 characters defined herein. By comparing to the literature and considering ontogenetic variation, we performed an analysis of character evolution in 70 mammalian species and reconstructed the nasal anatomy of the therian ancestor. Conclusions At birth, Marsupials have a complete but simple cupula nasi anterior, whereas placentals display a more diverse morphology due to reductions and variations of chondrocranial elements. The more compact nasal capsule in Marsupials is related to a long and strong fixation to the mother’s teat after birth. Within Marsupials and placentals, several derived characters distinguish major taxa, probably related to developmental and functional constraints. The reconstructed ancestral anatomy of the cupula nasi anterior supports the hypothesis that the therian ancestor was placental-like and that the marsupial lifestyle is more derived.
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On the development of the chondrocranium and the histological anatomy of the head in perinatal stages of marsupial mammals
Zoological Letters, 2017Co-Authors: Marcelo R. Sánchez-villagra, Analía M. ForasiepiAbstract:An overview of the literature on the chondrocranium of marsupial mammals reveals a relative conservatism in shape and structures. We document the histological cranial anatomy of individuals representing Monodelphis domestica , Dromiciops gliroides , Perameles sp. and Macropus eugenii . The marsupial chondrocranium is generally characterized by the great breadth of the lamina basalis, absence of pila metoptica and large otic capsules. Its most anterior portion (cupula nasi anterior) is robust, and anterior to it there are well-developed tactile sensory structures, functionally important in the neonate. Investigations of ossification centers at and around the nasal septum are needed to trace the presence of certain bones (e.g., mesethmoid, parasphenoid) across marsupial taxa. In many adult Marsupials, the tympanic floor is formed by at least three bones: alisphenoid (alisphenoid tympanic process), ectotympanic and petrosal (rostral and caudal tympanic processes); the squamosal also contributes in some diprotodontians. The presence of an entotympanic in Marsupials has not been convincingly demonstrated. The tubal element surrounding the auditory tube in most Marsupials is fibrous connective tissue rather than cartilage; the latter is the case in most placentals recorded to date. However, we detected fibrocartilage in a late juvenile of Dromiciops , and a similar tissue has been reported for Tarsipes . Contradictory reports on the presence of the tegmen tympani can be found in the literature. We describe a small tegmen tympani in Macropus . Several heterochronic shifts in the timing of development of the chondocranium and associated structures (e.g., nerves, muscles) and in the ossification sequence have been interpreted as largely being influenced by functional requirements related to the altriciality of the newborn marsupial during early postnatal life. Comparative studies of chondocranial development of mammals can benefit from a solid phylogenetic framework, research on non-classical model organisms, and integration with imaging and sectional data derived from computer-tomography.
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Why are There Fewer Marsupials than Placentals? On the Relevance of Geography and Physiology to Evolutionary Patterns of Mammalian Diversity and Disparity
Journal of Mammalian Evolution, 2013Co-Authors: Marcelo R. Sánchez-villagraAbstract:Placental mammals occupy a larger morphospace and are taxonomically more diverse than Marsupials by an order of magnitude, as shown by quantitative and phylogenetic studies of several character complexes and clades. Many have suggested that life history acts as a constraint on the evolution of marsupial morphology. However, the frequent circumvention of constraints suggests that the pattern of morphospace occupation in Marsupials is more a reflection of lack of ecological opportunity than one of biases in the production of variants during development. Features of marsupial physiology are a potential source of biases in the evolution of the group; these could be coupled with past macroevolutionary patterns that followed conditions imposed by global temperature changes. This is evident at the K/Pg boundary and at the Eocene/Oligocene boundary. The geographic pattern of taxonomic and morphological diversity in placental clades mirrors that of extant placentals as a whole versus Marsupials: placentals of northern origin are more diverse those of southern one and include the clades that are outliers in taxonomic (rodents and bats) and ecomorphological (whales and bats) richness.
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Cranial Anatomy of the Earliest Marsupials and the Origin of Opossums
PLOS ONE, 2009Co-Authors: Inés Horovitz, Thomas Martin, Jonathan I. Bloch, Sandrine Ladevèze, Cornelia Kurz, Marcelo R. Sánchez-villagraAbstract:Background: The early evolution of living Marsupials is poorly understood in part because the early offshoots of this group are known almost exclusively from jaws and teeth. Filling this gap is essential for a better understanding of the phylogenetic relationships among living Marsupials, the biogeographic pathways that led to their current distribution as well as the successive evolutionary steps that led to their current diversity, habits and various specializations that distinguish them from placental mammals. Methodology/Principal Findings: Here we report the first skull of a 55 million year old peradectid marsupial from the early Eocene of North America and exceptionally preserved skeletons of an Oligocene herpetotheriid, both representing critical groups to understand early marsupial evolution. A comprehensive phylogenetic cladistic analysis of Marsupialia including the new findings and close relatives of Marsupials show that peradectids are the sister group of living opossums and herpetotheriids are the sister group of all living Marsupials. Conclusions/Significance: The results imply that North America played an important role in early Cenozoic marsupial evolutionary history and may have even been the center of origin of living Marsupials and opossums. New data from the herpetotheriid postcranium support the view that the ancestral morphotype of Marsupialia was more terrestrial than opossums are. The resolution of the phylogenetic position of peradectids reveals an older calibration point for molecular estimates of divergence times among living Marsupials than those currently used.
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Developmental modularity and the marsupial-placental dichotomy
Journal of Experimental Zoology, 2009Co-Authors: Anjali Goswami, Vera Weisbecker, Marcelo R. Sánchez-villagraAbstract:The contrasting evolutionary histories of marsupial and placental mammals have often been attributed to their different reproductive strategies. The speciose placentals develop mainly in utero and have radiated into diverse niches, whereas Marsupials are born in a highly altricial state with immediate functional requirements and are limited in taxonomic, ecological, and morphological diversity. These differences have been tied to heterochrony, and it has been hypothesized that coordinated shifts in developmental timing occur among functionally- or developmentally related structures, such as forelimbs in Marsupials. We use new ossification sequence data for 11 marsupial and 14 placental species to assess the integration of first ossification timing among skeletal elements. Although cranial elements fail to demonstrate significant coordination, Marsupials and placentals differ markedly in postcranial integration. Marsupials display independent anterior and posterior developmental modules, whereas placentals show significant integration of the entire appendicular skeleton. This developmental integration of the placental postcranium is consistent with a recent study of phenotypic modularity in limbs of placental mammals, showing a potential correspondence between integration of developmental timing and of shape. The observed differences in postcranial integration between Marsupials and placentals may reflect the disparate evolutionary histories of these two mammalian clades.
Yukako Katsura - One of the best experts on this subject based on the ideXlab platform.
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the evolutionary process of mammalian sex determination genes focusing on marsupial srys
BMC Evolutionary Biology, 2018Co-Authors: Yukako Katsura, Hiroko Kondo, Janelle Ryan, Vincent R Harley, Yoko SattaAbstract:Maleness in mammals is genetically determined by the Y chromosome. On the Y chromosome SRY is known as the mammalian male-determining gene. Both placental mammals (Eutheria) and marsupial mammals (Metatheria) have SRY genes. However, only eutherian SRY genes have been empirically examined by functional analyses, and the involvement of marsupial SRY in male gonad development remains speculative. In order to demonstrate that the marsupial SRY gene is similar to the eutherian SRY gene in function, we first examined the sequence differences between marsupial and eutherian SRY genes. Then, using a parsimony method, we identify 7 marsupial-specific ancestral substitutions, 13 eutherian-specific ancestral substitutions, and 4 substitutions that occurred at the stem lineage of therian SRY genes. A literature search and molecular dynamics computational simulations support that the lineage-specific ancestral substitutions might be involved with the functional differentiation between marsupial and eutherian SRY genes. To address the function of the marsupial SRY gene in male determination, we performed luciferase assays on the testis enhancer of Sox9 core (TESCO) using the marsupial SRY. The functional assay shows that marsupial SRY gene can weakly up-regulate the luciferase expression via TESCO. Despite the sequence differences between the marsupial and eutherian SRY genes, our functional assay indicates that the marsupial SRY gene regulates SOX9 as a transcription factor in a similar way to the eutherian SRY gene. Our results suggest that SRY genes obtained the function of male determination in the common ancestor of Theria (placental mammals and Marsupials). This suggests that the marsupial SRY gene has a function in male determination, but additional experiments are needed to be conclusive.
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The evolutionary process of mammalian sex determination genes focusing on marsupial SRYs
BMC Evolutionary Biology, 2018Co-Authors: Yukako Katsura, Janelle Ryan, Hiroko X. Kondo, Vincent Harley, Yoko SattaAbstract:Background Maleness in mammals is genetically determined by the Y chromosome. On the Y chromosome SRY is known as the mammalian male-determining gene. Both placental mammals (Eutheria) and marsupial mammals (Metatheria) have SRY genes . However, only eutherian SRY genes have been empirically examined by functional analyses, and the involvement of marsupial SRY in male gonad development remains speculative. Results In order to demonstrate that the marsupial SRY gene is similar to the eutherian SRY gene in function, we first examined the sequence differences between marsupial and eutherian SRY genes. Then, using a parsimony method, we identify 7 marsupial-specific ancestral substitutions, 13 eutherian-specific ancestral substitutions, and 4 substitutions that occurred at the stem lineage of therian SRY genes. A literature search and molecular dynamics computational simulations support that the lineage-specific ancestral substitutions might be involved with the functional differentiation between marsupial and eutherian SRY genes. To address the function of the marsupial SRY gene in male determination, we performed luciferase assays on the testis enhancer of Sox9 core (TESCO) using the marsupial SRY . The functional assay shows that marsupial SRY gene can weakly up-regulate the luciferase expression via TESCO. Conclusions Despite the sequence differences between the marsupial and eutherian SRY genes, our functional assay indicates that the marsupial SRY gene regulates SOX9 as a transcription factor in a similar way to the eutherian SRY gene. Our results suggest that SRY genes obtained the function of male determination in the common ancestor of Theria (placental mammals and Marsupials). This suggests that the marsupial SRY gene has a function in male determination, but additional experiments are needed to be conclusive.
Robert D. Miller - One of the best experts on this subject based on the ideXlab platform.
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Marsupial immunology bounding ahead
Australian Journal of Zoology, 2013Co-Authors: Katherine Belov, Robert D. Miller, Julie M. Old, Lauren J. YoungAbstract:Marsupial immune responses were previously touted as ‘primitive’ but we now know that the marsupial immune system is complex and on par with that of eutherian mammals. In this manuscript we review the field of marsupial immunology, focusing on basic anatomy, developmental immunology, immunogenetics and evolution. We concentrate on advances to our understanding of marsupial immune gene architecture, made possible by the recent sequencing of the opossum, tammar wallaby and Tasmanian devil genomes. Characterisation of immune gene sequences now paves the way for the development of immunological assays that will allow us to more accurately study health and disease in Marsupials.
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A VpreB3 homologue in a marsupial, the gray short-tailed opossum, Monodelphis domestica
Immunogenetics, 2012Co-Authors: Xinxin Wang, Zuly E. Parra, Robert D. MillerAbstract:A VpreB surrogate light (SL) chain was identified for the first time in a marsupial, the opossum Monodelphis domestica . Comparing the opossum VpreB to homologues from eutherian (placental mammals) and avian species supported the marsupial gene being VpreB3 . VpreB3 is a protein that is not known to traffic to the cell surface as part of the pre-B cell receptor. Rather, VpreB3 associates with nascent immunoglobulin chains in the endoplasmic reticulum. Homologues of other known SL chains VpreB1 , VpreB2 , and λ5 , which are found in eutherian mammals, were not found in the opossum genome, nor have they been identified in the genomes of nonmammals. VpreB3 likely evolved from earlier gene duplication, independent of that which generated VpreB1 and VpreB2 in eutherians. The apparent absence of VpreB1, VpreB2, and λ5 in Marsupials suggests that an extracellular pre-B cell receptor containing SL chains, as it has been defined in humans and mice, may be unique to eutherian mammals. In contrast, the conservation of VpreB3 in Marsupials and its presence in nonmammals is consistent with previous hypotheses that it is playing a more primordial role in B cell development.
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Relationships Among the Families and Orders of Marsupials and the Major Mammalian Lineages Based on Recombination Activating Gene-1
Journal of Mammalian Evolution, 2004Co-Authors: Michelle L. Baker, John P. Wares, Gavan A. Harrison, Robert D. MillerAbstract:Controversies remain over the relationships among several of the marsupial families and between the three major extant lineages of mammals: Eutheria (placentals), Metatheria (Marsupials), and Prototheria (monotremes). Two opposing hypotheses place the Marsupials as either sister to the placental mammals (Theria hypothesis) or sister to the monotremes (Palimpsest or Marsupionta hypothesis). A nuclear gene that has proved useful for analyzing phylogenies of vertebrates is the recombination activation gene-1 (RAG1). RAG1 is a highly conserved gene in vertebrates and likely entered the genome by horizontal transfer early in the evolution of jawed vertebrates. Phylogenetic analyses were performed on RAG1 sequences from seven placentals, 28 Marsupials, and all three living monotreme species. Phylogenetic analyses of RAG1 sequences support many of the traditional relationships among the Marsupials and suggest a relationship between bandicoots (order Peramelina) and the marsupial mole (order Notoryctemorphia), two lineages whose position in the phylogenetic tree has been enigmatic. A sister relationship between South American shrew opossums (order Paucituberculata) and all other living marsupial orders is also suggested by RAG1. The relationship between the three major groups of mammals is consistent with the Theria hypothesis, with the monotremes as the sister group to a clade containing Marsupials and placentals.
