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Nicholas D. Holland - One of the best experts on this subject based on the ideXlab platform.
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the sensory peripheral nervous system in the tail of a cephalochordate studied by serial blockface scanning electron microscopy
The Journal of Comparative Neurology, 2020Co-Authors: Nicholas D. Holland, Ildiko M L SomorjaiAbstract:Serial blockface scanning electron microscopy (SBSEM) is used to describe the sensory peripheral nervous system (PNS) in the tail of a cephalochordate, Asymmetron lucayanum. The reconstructed region extends from the tail tip to the origin of the most posterior peripheral Nerves from the Dorsal Nerve Cord. As peripheral Nerves ramify within the dermis, all the nuclei along their course belong to glial cells. Invaginations in the glial cell cytoplasm house the neurites, an association reminiscent of the nonmyelinated Schwann cells of vertebrates. Peripheral Nerves pass from the dermis to the epidermis via small fenestrae in the sub-epidermal collagen fibril layer; most Nerves exit abruptly, but a few run obliquely within the collagen fibril layer for many micrometers before exiting. Within the epidermis, each Nerve begins ramifying repeatedly, but the branches are too small to be followed to their tips with SBSEM at low magnification (previous studies on other cephalochordates indicate that the branches end freely or in association with epidermal sensory cells). In Asymmetron, two morphological kinds of sensory cells are scattered in the epidermis, usually singly, but sometimes in pairs, evidently the recent progeny of a single precursor cell. The discussion considers the evolution of the sensory PNS in the phylum Chordata. In cephalochordates, Retzius bipolar neurons with intramedullary perikarya likely correspond to the Rohon-Beard cells of vertebrates. However, extramedullary neurons originating from ventral epidermis in cephalochordates (and presumably in ancestral chordates) contrast with vertebrate sensory neurons, which arise from placodes and neural crest.
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hybrids between the florida amphioxus branchiostoma floridae and the bahamas lancelet asymmetron lucayanum developmental morphology and chromosome counts
The Biological Bulletin, 2015Co-Authors: Nicholas D. Holland, Linda Z Holland, Alysha HeimbergAbstract:The cephalochordate genera Branchiostoma and Asymmetron diverged during the Mesozoic Era. In spite of the long separation of the parental clades, eggs of the Florida amphioxus, B. floridae, when fertilized with sperm of the Bahamas lancelet, A. lucayanum (and vice versa), develop through embryonic and larval stages. The larvae reach the chordate phylotypic stage (i.e., the pharyngula), characterized by a Dorsal Nerve Cord, notochord, perforate pharynx, and segmented trunk musculature. After about 2 weeks of larval development, the hybrids die, as do the A. lucayanum purebreds, although all were eating the same algal diet that sustains B. floridae purebreds through adulthood in the laboratory; it is thus unclear whether death of the hybrids results from incompatible parental genomes or an inadequate diet. The diploid chromosome count in A. lucayanum and B. floridae purebreds is, respectively, 34 and 38, whereas it is 36 in hybrids in either direction. The hybrid larvae exhibit several morphological charact...
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Evolutionary conservation of the presumptive neural plate markers AmphiSox1/2/3 and AmphiNeurogenin in the invertebrate chordate amphioxus.
Developmental biology, 2000Co-Authors: Linda Z Holland, Nicholas D. Holland, Michael Schubert, T NeumanAbstract:Amphioxus, as the closest living invertebrate relative of the vertebrates, can give insights into the evolutionary origin of the vertebrate body plan. Therefore, to investigate the evolution of genetic mechanisms for establishing and patterning the neuroectoderm, we cloned and determined the embryonic expression of two amphioxus transcription factors, AmphiSox1/2/3 and AmphiNeurogenin. These genes are the earliest known markers for presumptive neuroectoderm in amphioxus. By the early neurula stage, AmphiNeurogenin expression becomes restricted to two bilateral columns of segmentally arranged neural plate cells, which probably include precursors of motor neurons. This is the earliest indication of segmentation in the amphioxus Nerve Cord. Later, expression extends to Dorsal cells in the Nerve Cord, which may include precursors of sensory neurons. By the midneurula, AmphiSox1/2/3 expression becomes limited to the Dorsal part of the forming neural tube. These patterns resemble those of their vertebrate and Drosophila homologs. Taken together with the evolutionarily conserved expression of the dorsoventral patterning genes, BMP2/4 and chordin, in nonneural and neural ectoderm, respectively, of chordates and Drosophila, our results are consistent with the evolution of the chordate Dorsal Nerve Cord and the insect ventral Nerve Cord from a longitudinal Nerve Cord in a common bilaterian ancestor. However, AmphiSox1/2/3 differs from its vertebrate homologs in not being expressed outside the CNS, suggesting that additional roles for this gene have evolved in connection with gene duplication in the vertebrate lineage. In contrast, expression in the midgut of AmphiNeurogenin together with the gene encoding the insulin-like peptide suggests that amphioxus may have homologs of vertebrate pancreatic islet cells, which express neurogenin3. In addition, AmphiNeurogenin, like its vertebrate and Drosophila homologs, is expressed in apparent precursors of epidermal chemosensory and possibly mechanosensory cells, suggesting a common origin for protostome and deuterostome epidermal sensory cells in the ancestral bilaterian.
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Sequence and embryonic expression of the amphioxus engrailed gene (AmphiEn): the metameric pattern of transcription resembles that of its segment-polarity homolog in Drosophila
Development (Cambridge England), 1997Co-Authors: Linda Z Holland, M. Kene, Nic A. Williams, Nicholas D. HollandAbstract:Vertebrate segmentation has been proposed as an evolutionary inheritance either from some metameric protostome or from a more closely related deuterostome. To address this question, we studied the developmental expression of AmphiEn, the engrailed gene of amphioxus, the closest living invertebrate relative of the vertebrates. In neurula embryos of amphioxus, AmphiEn is expressed along the anteroposterior axis as metameric stripes, each located in the posterior part of a nascent or newly formed segment. This pattern resembles the expression stripes of the segment-polarity gene engrailed, which has a key role in establishing and maintaining the metameres in embryos of Drosophila and other metameric protostomes. Later, amphioxus embryos express AmphiEn in non-metameric patterns - transiently in the embryonic ectoderm and Dorsal Nerve Cord. Nerve Cord expression occurs in a few cells approximately midway along the rostrocaudal axis and also in a conspicuous group of anterior cells in the cerebral vesicle at a level previously identified as corresponding to the vertebrate diencephalon. Compared to vertebrate engrailed expression at the midbrain/hindbrain boundary, AmphiEn expression in the cerebral vesicle is relatively late. Thus, it is uncertain whether the cerebral vesicle expression marks the rostral end of the amphioxus hindbrain; if it does, then amphioxus may have little or no homolog of the vertebrate midbrain. The segmental expression of AmphiEn in forming somites suggests that the functions of engrailed homologs in establishing and maintaining a metameric body plan may have arisen only once during animal evolution. If so, the protostomes and deuterostomes probably shared a common segmented ancestor.
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Sequence and developmental expression of AmphiTob, an amphioxus homolog of vertebrate Tob in the PC3/BTG1/Tob family of tumor suppressor genes.
Developmental dynamics : an official publication of the American Association of Anatomists, 1997Co-Authors: Nicholas D. Holland, Shi-cui Zhang, Matthew D. Clark, Georgia Panopoulou, Hans Lehrach, Linda Z HollandAbstract:Tob is a member of the PC3/BTG1/Tob family of vertebrate tumor suppressor genes; its expression is known to inhibit proliferation of cells in vitro, but its possible roles during normal development have not been investigated previously. The present study concerns the structure and developmental expression of AmphiTob in an invertebrate chordate, amphioxus. This is the first investigation of any Tob gene during embryological development. The 311 amino acid AmphiTob protein is similar to vertebrate Tob but lacks the C-terminal PQ-rich domain of the latter. In early embryos of amphioxus, in situ hybridization first reveals AmphiTob expression in the hypoblast at the gastrula stage on the likely Dorsal side of the embryo. During subsequent development, expression is seen in several tissues of the ectoderm, mesoderm, and endoderm. The most striking expression domains are in the developing somitic musculature and Dorsal Nerve Cord. In the medial wall of each somite, AmphiTob is expressed strongly by cells destined to differentiate into the axial trunk muscles; this pattern persists until late in the larval stage, evidently because undifferentiated cells are continually becoming myogenic as the muscles grow. Nerve Cord cells conspicuously transcribe AmphiTob from the late neurula until the early larval stage: Expression occurs in a few cells scattered along the Nerve Cord and in a group of cells located in the cerebral vesicle (in a region presumably homologous to the vertebrate diencephalic forebrain). During development, an intense and transitory transcription of AmphiTob may be an early event in cells exiting the cell cycle in preparation for differentiation. Dev. Dyn. 1997;210:11–18. © 1997 Wiley-Liss, Inc.
Linda Z Holland - One of the best experts on this subject based on the ideXlab platform.
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hybrids between the florida amphioxus branchiostoma floridae and the bahamas lancelet asymmetron lucayanum developmental morphology and chromosome counts
The Biological Bulletin, 2015Co-Authors: Nicholas D. Holland, Linda Z Holland, Alysha HeimbergAbstract:The cephalochordate genera Branchiostoma and Asymmetron diverged during the Mesozoic Era. In spite of the long separation of the parental clades, eggs of the Florida amphioxus, B. floridae, when fertilized with sperm of the Bahamas lancelet, A. lucayanum (and vice versa), develop through embryonic and larval stages. The larvae reach the chordate phylotypic stage (i.e., the pharyngula), characterized by a Dorsal Nerve Cord, notochord, perforate pharynx, and segmented trunk musculature. After about 2 weeks of larval development, the hybrids die, as do the A. lucayanum purebreds, although all were eating the same algal diet that sustains B. floridae purebreds through adulthood in the laboratory; it is thus unclear whether death of the hybrids results from incompatible parental genomes or an inadequate diet. The diploid chromosome count in A. lucayanum and B. floridae purebreds is, respectively, 34 and 38, whereas it is 36 in hybrids in either direction. The hybrid larvae exhibit several morphological charact...
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The basal chordate amphioxus as a simple model for elucidating developmental mechanisms in vertebrates.
Birth defects research. Part C Embryo today : reviews, 2008Co-Authors: Demian Koop, Linda Z HollandAbstract:This review examines the basal chordate, amphioxus, as a simple model for providing insights into the development and evolution of the vertebrates, with which it shares many features, including a pharynx perforated with gill slits, a Dorsal Nerve Cord, segmented muscles, and a notochord. Conversely, amphioxus is simpler than vertebrates in lacking neural crest and paired cephalic sensory organs. Amphioxus embryos are less derived than those of vertebrates, because it lacks large quantities of yolk and/or extra-embryonic tissues. Embryogenesis involves only a simple folding of tissue layers. In addition, the amphioxus genome lacks the large-scale gene duplications of vertebrates. However, in spite of the comparative simplicity of amphioxus, its developmental mechanisms are proving to be highly conserved with those of vertebrates. Thus, studies of amphioxus development can shed light on similar, but more complex, development of vertebrates. Such studies are especially interesting for their insights into the genetic basis of craniofacial birth defects in humans.
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Evolutionary conservation of the presumptive neural plate markers AmphiSox1/2/3 and AmphiNeurogenin in the invertebrate chordate amphioxus.
Developmental biology, 2000Co-Authors: Linda Z Holland, Nicholas D. Holland, Michael Schubert, T NeumanAbstract:Amphioxus, as the closest living invertebrate relative of the vertebrates, can give insights into the evolutionary origin of the vertebrate body plan. Therefore, to investigate the evolution of genetic mechanisms for establishing and patterning the neuroectoderm, we cloned and determined the embryonic expression of two amphioxus transcription factors, AmphiSox1/2/3 and AmphiNeurogenin. These genes are the earliest known markers for presumptive neuroectoderm in amphioxus. By the early neurula stage, AmphiNeurogenin expression becomes restricted to two bilateral columns of segmentally arranged neural plate cells, which probably include precursors of motor neurons. This is the earliest indication of segmentation in the amphioxus Nerve Cord. Later, expression extends to Dorsal cells in the Nerve Cord, which may include precursors of sensory neurons. By the midneurula, AmphiSox1/2/3 expression becomes limited to the Dorsal part of the forming neural tube. These patterns resemble those of their vertebrate and Drosophila homologs. Taken together with the evolutionarily conserved expression of the dorsoventral patterning genes, BMP2/4 and chordin, in nonneural and neural ectoderm, respectively, of chordates and Drosophila, our results are consistent with the evolution of the chordate Dorsal Nerve Cord and the insect ventral Nerve Cord from a longitudinal Nerve Cord in a common bilaterian ancestor. However, AmphiSox1/2/3 differs from its vertebrate homologs in not being expressed outside the CNS, suggesting that additional roles for this gene have evolved in connection with gene duplication in the vertebrate lineage. In contrast, expression in the midgut of AmphiNeurogenin together with the gene encoding the insulin-like peptide suggests that amphioxus may have homologs of vertebrate pancreatic islet cells, which express neurogenin3. In addition, AmphiNeurogenin, like its vertebrate and Drosophila homologs, is expressed in apparent precursors of epidermal chemosensory and possibly mechanosensory cells, suggesting a common origin for protostome and deuterostome epidermal sensory cells in the ancestral bilaterian.
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Sequence and embryonic expression of the amphioxus engrailed gene (AmphiEn): the metameric pattern of transcription resembles that of its segment-polarity homolog in Drosophila
Development (Cambridge England), 1997Co-Authors: Linda Z Holland, M. Kene, Nic A. Williams, Nicholas D. HollandAbstract:Vertebrate segmentation has been proposed as an evolutionary inheritance either from some metameric protostome or from a more closely related deuterostome. To address this question, we studied the developmental expression of AmphiEn, the engrailed gene of amphioxus, the closest living invertebrate relative of the vertebrates. In neurula embryos of amphioxus, AmphiEn is expressed along the anteroposterior axis as metameric stripes, each located in the posterior part of a nascent or newly formed segment. This pattern resembles the expression stripes of the segment-polarity gene engrailed, which has a key role in establishing and maintaining the metameres in embryos of Drosophila and other metameric protostomes. Later, amphioxus embryos express AmphiEn in non-metameric patterns - transiently in the embryonic ectoderm and Dorsal Nerve Cord. Nerve Cord expression occurs in a few cells approximately midway along the rostrocaudal axis and also in a conspicuous group of anterior cells in the cerebral vesicle at a level previously identified as corresponding to the vertebrate diencephalon. Compared to vertebrate engrailed expression at the midbrain/hindbrain boundary, AmphiEn expression in the cerebral vesicle is relatively late. Thus, it is uncertain whether the cerebral vesicle expression marks the rostral end of the amphioxus hindbrain; if it does, then amphioxus may have little or no homolog of the vertebrate midbrain. The segmental expression of AmphiEn in forming somites suggests that the functions of engrailed homologs in establishing and maintaining a metameric body plan may have arisen only once during animal evolution. If so, the protostomes and deuterostomes probably shared a common segmented ancestor.
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Sequence and developmental expression of AmphiTob, an amphioxus homolog of vertebrate Tob in the PC3/BTG1/Tob family of tumor suppressor genes.
Developmental dynamics : an official publication of the American Association of Anatomists, 1997Co-Authors: Nicholas D. Holland, Shi-cui Zhang, Matthew D. Clark, Georgia Panopoulou, Hans Lehrach, Linda Z HollandAbstract:Tob is a member of the PC3/BTG1/Tob family of vertebrate tumor suppressor genes; its expression is known to inhibit proliferation of cells in vitro, but its possible roles during normal development have not been investigated previously. The present study concerns the structure and developmental expression of AmphiTob in an invertebrate chordate, amphioxus. This is the first investigation of any Tob gene during embryological development. The 311 amino acid AmphiTob protein is similar to vertebrate Tob but lacks the C-terminal PQ-rich domain of the latter. In early embryos of amphioxus, in situ hybridization first reveals AmphiTob expression in the hypoblast at the gastrula stage on the likely Dorsal side of the embryo. During subsequent development, expression is seen in several tissues of the ectoderm, mesoderm, and endoderm. The most striking expression domains are in the developing somitic musculature and Dorsal Nerve Cord. In the medial wall of each somite, AmphiTob is expressed strongly by cells destined to differentiate into the axial trunk muscles; this pattern persists until late in the larval stage, evidently because undifferentiated cells are continually becoming myogenic as the muscles grow. Nerve Cord cells conspicuously transcribe AmphiTob from the late neurula until the early larval stage: Expression occurs in a few cells scattered along the Nerve Cord and in a group of cells located in the cerebral vesicle (in a region presumably homologous to the vertebrate diencephalic forebrain). During development, an intense and transitory transcription of AmphiTob may be an early event in cells exiting the cell cycle in preparation for differentiation. Dev. Dyn. 1997;210:11–18. © 1997 Wiley-Liss, Inc.
Peter W. H. Holland - One of the best experts on this subject based on the ideXlab platform.
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Molecular phylogeny: My sister is a sea squirt?
Heredity, 2006Co-Authors: Peter W. H. HollandAbstract:Sir Ray Lankester was lying on the deck of a research vessel in heaving seas, green with sea sickness. As the latest trawl of sea creatures was emptied on to the deck Lankester caught a glimpse of a small silvery animal, 'a semitransparent, oblong, flattened thing, like a small paper knife'. He wrote 'I recognised him and immediately felt restored to well being' (Lankester, 1915). This was the first living specimen he had seen of the lancelet or amphioxus; an animal of considerable fame, and sufficiently exciting to cure his affliction. Lankester's subsequent research on this animal, together with work by Willey, Goodrich and others, showed that amphioxus, although resembling a small fish in general form, is not a true vertebrate, but is an invertebrate relative of the vertebrates. It shares many anatomical characters with vertebrates, notably segmented muscle blocks along its flanks, Dorsal Nerve Cord, notochord and gill slits. It lacks a vertebral column and an elaborate head region.
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An amphioxus homeobox gene: sequence conservation, spatial expression during development and insights into vertebrate evolution
Development (Cambridge England), 1992Co-Authors: Peter W. H. Holland, Linda Z Holland, Nicola A. Williams, Nicholas D. HollandAbstract:The embryology of amphioxus has much in common with vertebrate embryology, reflecting a close phylogenetic relationship between the two groups. Amphioxus embryology is simpler in several key respects, however, including a lack of pronounced craniofacial morphogenesis. To gain an insight into the molecular changes that accompanied the evolution of vertebrate embryology, and into the relationship between the amphioxus and vertebrate body plans, we have undertaken the first molecular level investigation of amphioxus embryonic development. We report the cloning, complete DNA sequence determination, sequence analysis and expression analysis of an amphioxus homeobox gene, AmphiHox3, evolutionarily homologous to the third-most 3′ paralogous group of mammalian Hox genes. Sequence comparison to a mammalian homologue, mouse Hox-2.7 (HoxB3), reveals several stretches of amino acid conservation within the deduced protein sequences. Whole mount in situ hybridization reveals localized expression of AmphiHox3 in the posterior mesoderm (but not in the somites), and region-specific expression in the Dorsal Nerve Cord, of amphioxus neurulae, later embryos and larvae. The anterior limit to expression in the Nerve Cord is at the level of the four/five somite boundary at the neurula stage, and stabilises to just anterior to the first Nerve Cord pigment spot to form. Comparison to the anterior expression boundary of mouse Hox-2.7 (HoxB3) and related genes suggests that the vertebrate brain is homologous to an extensive region of the amphioxus Nerve Cord that contains the cerebral vesicle (a region at the extreme rostral tip) and extends posterior to somite four.(ABSTRACT TRUNCATED AT 250 WORDS)
Noriyuki Satoh - One of the best experts on this subject based on the ideXlab platform.
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Spatial expression of the amphioxus homologue of Brachyury (T) gene during early embryogenesis of Branchiostoma belcheri
Development Growth and Differentiation, 1995Co-Authors: Kouzou Terazawa, Noriyuki SatohAbstract:Amphioxus are primitive chordates that share several common anatomical features with vertebrates, such as a notochord and a Dorsal Nerve Cord. The Brachyury (T) gene is required for notochord differentiation in vertebrates and an ascidian homologue of this gene is expressed in notochord cells at the time of developmental fate restriction. To gain insight into the molecular and developmental mechanisms underlying the evolution of chordates, we amplified a cDNA fragment for an amphioxus homologue (BbT1) of the mouse T gene, with which we examined the spatial expression of the BbT1 gene. In situ hybridization showed that BbT1 transcript was undetectable in eggs, as well as in early embryos at the cleavage and blastula stages. Distinct hybridization signals were first evident in the mesoderm of gastrulae but neither the ectoderm nor endoderm showed the signals. As development proceeded to the neurula stage, the signals became conspicuous in the primordial somite at the dorsolateral wall of the archenteron, while the primordial notochord at the dorsomedian wall of the archenteron emitted less intense hybridization signals. These results suggested that the T gene is conserved by amphioxus and that the BbT1 gene is expressed in the mesodermal region of the gastrula and neurula.
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A sea urchin homologue of the chordate Brachyury (T) gene is expressed in the secondary mesenchyme founder cells
Development (Cambridge England), 1995Co-Authors: Yoshito Harada, Hitoyoshi Yasuo, Noriyuki SatohAbstract:Chordates are thought to have emerged from some common ancestor of deuterostomes by organizing shared anatomical and embryological features including a notochord, a Dorsal Nerve Cord and pharyngeal gill slits. Because the notochord is the most prominent feature of chordates and because the Brachyury (T) gene is essential for notochord formation, the T gene is a key molecular probe with which to explore the origin and evolution of chordates. We investigated whether the sea urchin (echinoderm) conserves the T gene and, if so, where the sea urchin T gene is expressed. A cDNA clone for the sea urchin T (HpTa) gene contained a long open reading frame that encodes a polypeptide of 434 amino acids. Although the overall degree of amino acid identity was not very high (52%, sea urchin/mouse), in the T domain of the N terminus the amino acid identity was 73% (sea urchin/mouse). The HpTa gene is present as a single copy per haploid genome. As with the chordate T gene, the expression of HpTa is transient, being first detected in the swimming blastula, maximally transcribed in the gastrula, decreasing at the prism larval stage and barely detectable at the pluteus larval stage. HpTa transcripts were found in the secondary mesenchyme founder cells, vegetal plate of the mesenchyme blastula, extending tip of the invaginating archenteron and, finally, the secondary mesenchyme cells at the late-gastrula stage.(ABSTRACT TRUNCATED AT 250 WORDS)
David M. Miller - One of the best experts on this subject based on the ideXlab platform.
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Transcriptional Control of Synaptic Remodeling through Regulated Expression of an Immunoglobulin Superfamily Protein.
Current biology : CB, 2015Co-Authors: Alison Philbrook, Rebecca Mcwhirter, Christopher V. Gabel, Daniel G. Taub, Maximilian H. Carter, Isabella M. Hanna, Michael M. Francis, David M. MillerAbstract:Neural circuits are actively remodeled during brain development, but the molecular mechanisms that trigger circuit refinement are poorly understood. Here, we describe a transcriptional program in C. elegans that regulates expression of an Ig domain protein, OIG-1, to control the timing of synaptic remodeling. DD GABAergic neurons reverse polarity during larval development by exchanging the locations of pre- and postsynaptic components. In newly born larvae, DDs receive cholinergic inputs in the Dorsal Nerve Cord. These inputs are switched to the ventral side by the end of the first larval (L1) stage. VD class GABAergic neurons are generated in the late L1 and are postsynaptic to cholinergic neurons in the Dorsal Nerve Cord but do not remodel. We investigated remodeling of the postsynaptic apparatus in DD and VD neurons using targeted expression of the acetylcholine receptor (AChR) subunit, ACR-12::GFP. We determined that OIG-1 antagonizes the relocation of ACR-12 from the Dorsal side in L1 DD neurons. During the L1/L2 transition, OIG-1 is downregulated in DD neurons by the transcription factor IRX-1/Iroquois, allowing the repositioning of synaptic inputs to the ventral side. In VD class neurons, which normally do not remodel, the transcription factor UNC-55/COUP-TF turns off IRX-1, thus maintaining high levels of OIG-1 to block the removal of Dorsally located ACR-12 receptors. OIG-1 is secreted from GABA neurons, but its anti-plasticity function is cell autonomous and may not require secretion. Our study provides a novel mechanism by which synaptic remodeling is set in motion through regulated expression of an Ig domain protein.