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Charles G Sagerstrom - One of the best experts on this subject based on the ideXlab platform.
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Targeted germ line disruptions reveal general and species-specific roles for paralog group 1 hox genes in zebrafish.
BMC developmental biology, 2014Co-Authors: Steven E Weicksel, Ankit Gupta, Denise A Zannino, Scot A Wolfe, Charles G SagerstromAbstract:The developing vertebrate hindbrain is transiently segmented into Rhombomeres by a process requiring Hox activity. Hox genes control specification of Rhombomere fates, as well as the stereotypic differentiation of Rhombomere-specific neuronal populations. Accordingly, germ line disruption of the paralog group 1 (PG1) Hox genes Hoxa1 and Hoxb1 causes defects in hindbrain segmentation and neuron formation in mice. However, antisense-mediated interference with zebrafish hoxb1a and hoxb1b (analogous to murine Hoxb1 and Hoxa1, respectively) produces phenotypes that are qualitatively and quantitatively distinct from those observed in the mouse. This suggests that PG1 Hox genes may have species-specific functions, or that anti-sense mediated interference may not completely inactivate Hox function in zebrafish. Using zinc finger and TALEN technologies, we disrupted hoxb1a and hoxb1b in the zebrafish germ line to establish mutant lines for each gene. We find that zebrafish hoxb1a germ line mutants have a more severe phenotype than reported for Hoxb1a antisense treatment. This phenotype is similar to that observed in Hoxb1 knock out mice, suggesting that Hoxb1/hoxb1a have the same function in both species. Zebrafish hoxb1b germ line mutants also have a more severe phenotype than reported for hoxb1b antisense treatment (e.g. in the effect on Mauthner neuron differentiation), but this phenotype differs from that observed in Hoxa1 knock out mice (e.g. in the specification of Rhombomere 5 (r5) and r6), suggesting that Hoxa1/hoxb1b have species-specific activities. We also demonstrate that Hoxb1b regulates nucleosome organization at the hoxb1a promoter and that retinoic acid acts independently of hoxb1b to activate hoxb1a expression. We generated several novel germ line mutants for zebrafish hoxb1a and hoxb1b. Our analyses indicate that Hoxb1 and hoxb1a have comparable functions in zebrafish and mouse, suggesting a conserved function for these genes. In contrast, while Hoxa1 and hoxb1b share functions in the formation of r3 and r4, they differ with regards to r5 and r6, where Hoxa1 appears to control formation of r5, but not r6, in the mouse, whereas hoxb1b regulates formation of r6, but not r5, in zebrafish. Lastly, our data reveal independent regulation of hoxb1a expression by retinoic acid and Hoxb1b in zebrafish.
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Targeted germ line disruptions reveal general and species-specific roles for paralog group 1 hox genes in zebrafish
BMC Developmental Biology, 2014Co-Authors: Steven E Weicksel, Ankit Gupta, Denise A Zannino, Scot A Wolfe, Charles G SagerstromAbstract:Background The developing vertebrate hindbrain is transiently segmented into Rhombomeres by a process requiring Hox activity. Hox genes control specification of Rhombomere fates, as well as the stereotypic differentiation of Rhombomere-specific neuronal populations. Accordingly, germ line disruption of the paralog group 1 (PG1) Hox genes Hoxa1 and Hoxb1 causes defects in hindbrain segmentation and neuron formation in mice. However, antisense-mediated interference with zebrafish hoxb1a and hoxb1b (analogous to murine Hoxb1 and Hoxa1 , respectively) produces phenotypes that are qualitatively and quantitatively distinct from those observed in the mouse. This suggests that PG1 Hox genes may have species-specific functions, or that anti-sense mediated interference may not completely inactivate Hox function in zebrafish. Results Using zinc finger and TALEN technologies, we disrupted hoxb1a and hoxb1b in the zebrafish germ line to establish mutant lines for each gene. We find that zebrafish hoxb1a germ line mutants have a more severe phenotype than reported for Hoxb1a antisense treatment. This phenotype is similar to that observed in Hoxb1 knock out mice, suggesting that Hoxb1/hoxb1a have the same function in both species. Zebrafish hoxb1b germ line mutants also have a more severe phenotype than reported for hoxb1b antisense treatment (e.g. in the effect on Mauthner neuron differentiation), but this phenotype differs from that observed in Hoxa1 knock out mice (e.g. in the specification of Rhombomere 5 (r5) and r6), suggesting that Hoxa1/hoxb1b have species-specific activities. We also demonstrate that Hoxb1b regulates nucleosome organization at the hoxb1a promoter and that retinoic acid acts independently of hoxb1b to activate hoxb1a expression. Conclusions We generated several novel germ line mutants for zebrafish hoxb1a and hoxb1b. Our analyses indicate that Hoxb1 and hoxb1a have comparable functions in zebrafish and mouse, suggesting a conserved function for these genes. In contrast, while Hoxa1 and hoxb1b share functions in the formation of r3 and r4, they differ with regards to r5 and r6, where Hoxa1 appears to control formation of r5, but not r6, in the mouse, whereas hoxb1b regulates formation of r6, but not r5, in zebrafish. Lastly, our data reveal independent regulation of hoxb1a expression by retinoic acid and Hoxb1b in zebrafish.
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paralog group 1 hox genes regulate Rhombomere 5 6 expression of vhnf1 a repressor of rostral hindbrain fates in a meis dependent manner
Developmental Biology, 2004Co-Authors: Seongkyu Choe, Charles G SagerstromAbstract:Abstract The vertebrate hindbrain is segmented into an array of Rhombomeres (r), but it remains to be fully understood how segmentation is achieved. Here we report that reducing meis function transforms the caudal hindbrain to an r4-like fate, and we exploit this experimental state to explore how r4 versus r5–r6 segments are set aside. We demonstrate that r4 transformation of the caudal hindbrain is mediated by paralog group 1 (PG1) hox genes and can be repressed by vhnf1 , a gene expressed in r5–r6. We further find that vhnf1 expression is regulated by PG1 hox genes in a meis -dependent manner. This implies that PG1 hox genes not only induce r4 fates throughout the caudal hindbrain, but also induce expression of vhnf1 , which then represses r4 fates in the future r5–r6. Our results further indicate that r4 transformation of the caudal hindbrain occurs at intermediate levels of meis function, while extensive removal of meis function produces a hindbrain completely devoid of segments, suggesting that different hox -dependent processes may have distinct meis requirements. Notably, reductions in the function of another Hox cofactor, pbx , have not been reported to transform the caudal hindbrain, suggesting that Meis and Pbx proteins may also function differently in their roles as Hox cofactors.
A. Lumsden - One of the best experts on this subject based on the ideXlab platform.
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ORGANIZATION AND DEVELOPMENT OF FACIAL MOTOR NEURONS IN THE KREISLER MUTANT MOUSE
The European journal of neuroscience, 1997Co-Authors: Ian J. Mckay, Julian Lewis, A. LumsdenAbstract:The adult facial nerve contains the axons from two populations of efferent neurons. First, the branchiomotor efferent neurons that innervate the muscles of the second arch. These neurons project out of the hindbrain in the motor root and form the facial motor nuclei. Second, the preganglionic efferent neurons that innervate the submandibular and pterygopalatine ganglia. These neurons project from the hindbrain via the intermediate nerve and form the superior salivatory nucleus. The motor neurons of the facial nerve are known to originate within Rhombomeres 4 and 5. In the kreisler mouse mutant there is a specific disruption of the hindbrain Rhombomeres 5 and 6 appear to be absent. To investigate changes in the organization of the facial motor neurons in this mutant, we have used lipophilic dyes to trace the facial motor components both retrogradely and anterogradely. As expected, facial motor neurons are missing from Rhombomere 5 in this mutant. In addition, the loss of these neurons correlates with the specific loss of the superior salivatory nucleus. In contrast, the branchiomeric neurons, that originate in Rhombomere 4, appear to develop normally. This includes the caudal migration of their cell bodies forming the genu of the facial nerve. Our studies confirm that Rhombomeres are critical to hindbrain development and that they are the fundamental unit at which motor neurons are specified.
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Two Rhombomeres are altered in Hoxa-1 mutant mice.
Development (Cambridge England), 1993Co-Authors: E Mark, E Ruberte, T Lufkin, J Vonesch, J Olivo, P. Dolle, Philippe Gorry, A. Lumsden, P. ChambonAbstract:This study provides a detailed description of the anatomical defects in the Hoxa-1-/- mutant mice previously generated in our laboratory (T. Lufkin, A. Dierich, M. LeMeur, M. Mark and P. Chambon, 1991; Cell 66, 1105-1119). Three-dimensional reconstructions of the Hoxa-1-/- rhombencephalon reveals that it bears only five rhombomeric structures (ie. morphological segments) instead of the normal seven. The first three of these Rhombomeres appear normal as judged from the distribution pattern of CRABPI transcripts in the neurectoderm and from the histological analysis of the cranial nerve components derived from these structures. In contrast, the neural-crest-cell-free region normally located opposite Rhombomere 5 is lacking in Hoxa-1-/- embryos, and motor neurons of the facial and abducens nerves, which normally differentiate within Rhombomeres 4, 5 and 6, are missing in Hoxa-1-/- fetuses. These morphological data, combined with the determination of the molecular positional identities of the Rhombomeres 4 and 5 (P. Dollé, T. Lufkin, R. Krumlauf, M. Mark, D. Duboule and P. Chambon, 1993; Proc. Natl. Acad. Sci. USA, in press), suggest that Rhombomere 4 is markedly reduced, whereas Rhombomere 5 is almost absent. Thus, the remnants of Rhombomeres 4 and 5 appear to be fused caudally with Rhombomere 6 to form a single fourth rhombomeric structure. Moreover, the migration of neural crest cells contributing to the glossopharyngeal and vagus nerves occurs in a more rostral position, resulting in abnormalities of these cranial nerves, which were visualized by whole-mount anti-neurofilament immunostaining. The mutual relationship along the rostrocaudal axis between the otic pit and the neuroepithelial site of int-2 protein secretion (a putative otogenic cue) is not significantly changed in Hoxa-1-/- embryos. However, the abnormal relationship between the rhombencephalon and the epithelial inner ear may account for the aplasia and faulty differentiation of the membranous labyrinth, the disruption of the cartilaginous otic capsule and the disorganisation of some middle ear structures. This phenotype is compared with that of the Hoxa-1-/- mutants generated by O. Chisaka, T. S. Musci and M. R. Capecchi, 1992 (Nature 335, 516-520) and with that of the mice homozygous for the kreisler mutation.
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Two Rhombomeres are altered in Hoxa-1 mutant mice.
Development (Cambridge England), 1993Co-Authors: Manuel Mark, T Lufkin, J Vonesch, P. Dolle, Philippe Gorry, A. Lumsden, Esther Ruberte, Jean-christophe Olivo, Pierre ChambonAbstract:This study provides a detailed description of the anatomical defects in the Hoxa-1-/- mutant mice previously generated in our laboratory (T. Lufkin, A. Dierich, M. LeMeur, M. Mark and P. Chambon, 1991; Cell 66, 1105-1119). Three-dimensional reconstructions of the Hoxa-1-/- rhombencephalon reveals that it bears only five rhombomeric structures (ie. morphological segments) instead of the normal seven. The first three of these Rhombomeres appear normal as judged from the distribution pattern of CRABPI transcripts in the neurectoderm and from the histological analysis of the cranial nerve components derived from these structures. In contrast, the neural-crest-cell-free region normally located opposite Rhombomere 5 is lacking in Hoxa-1-/- embryos, and motor neurons of the facial and abducens nerves, which normally differentiate within Rhombomeres 4, 5 and 6, are missing in Hoxa-1-/- fetuses. These morphological data, combined with the determination of the molecular positional identities of the Rhombomeres 4 and 5 (P. Dolle, T. Lufkin, R. Krumlauf, M. Mark, D. Duboule and P. Chambon, 1993; Proc. Natl. Acad. Sci. USA, in press), suggest that Rhombomere 4 is markedly reduced, whereas Rhombomere 5 is almost absent. Thus, the remnants of Rhombomeres 4 and 5 appear to be fused caudally with Rhombomere 6 to form a single fourth rhombomeric structure. Moreover, the migration of neural crest cells contributing to the glossopharyngeal and vagus nerves occurs in a more rostral position, resulting in abnormalities of these cranial nerves, which were visualized by whole-mount anti-neurofilament immunostaining. The mutual relationship along the rostrocaudal axis between the otic pit and the neuroepithelial site of int-2 protein secretion (a putative otogenic cue) is not significantly changed in Hoxa-1-/- embryos. However, the abnormal relationship between the rhombencephalon and the epithelial inner ear may account for the aplasia and faulty differentiation of the membranous labyrinth, the disruption of the cartilaginous otic capsule and the disorganisation of some middle ear structures. This phenotype is compared with that of the Hoxa-1-/- mutants generated by O. Chisaka, T. S. Musci and M. R. Capecchi, 1992 (Nature 335, 516-520) and with that of the mice homozygous for the kreisler mutation.
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Rhombomere-specific origin of the contralateral vestibulo-acoustic efferent neurons and their migration across the embryonic midline
Neuron, 1993Co-Authors: Horst Simon, A. LumsdenAbstract:Abstract The bilateral efferent supply to the inner ear receptor fields is located in the hindbrain. In ovo injections of Dil into the common facial/vestibulo-acoustic nerve root at 3 days of chick development (stage 16) followed by analysis at 7 days has revealed the origin of the contralateral efferent neurons of the inner ear and their relation to the transient hindbrain Rhombomeres. These neurons have a Rhombomere 4-specific origin and form their commissure not by axonal outgrowth but, unusually, by transmedian cell migration into the contralateral Rhombomere 4 and Rhombomere 5. Neurons first project their axons from the ipsilateral basal plate through the VII/VIIIth nerve exit point and then migrate in the opposite direction, crossing the floor plate at stage 19–21. This Rhombomere-specific cell behavior provides evidence at the cellular level that segmentation is intimately involved in establishing the pattern of this region of the CNS.
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Formation and regeneration of Rhombomere boundaries in the developing chick hindbrain.
Development (Cambridge England), 1991Co-Authors: Sarah Guthrie, A. LumsdenAbstract:Development in the chick hindbrain is founded on a segmented pattern. Groups of cells are allocated to particular segmental levels early in development, the cells of each segment (Rhombomere) mixing freely with each other, but not with those of adjacent segments. After Rhombomere formation, cells in the boundary regions become increasingly specialised. Rhombomeres are thus separate territories that will ultimately pursue different developmental fates. We are investigating the mechanisms that establish and maintain the pattern of Rhombomeres and their boundaries. Donor-to-host transplantation experiments were used to confront tissue from different axial levels within the hindbrain. The frequency of boundary regeneration and patterning in the hindbrain was then assessed, based on gross morphology, arrangement of motor neurons and immunohistochemistry. We found that when Rhombomeres from adjacent positions or positions three Rhombomeres distant from one another were confronted, a normal boundary was invariably reconstructed. Juxtaposition of Rhombomere 5 with 7 also yielded a new boundary. By contrast, donor and host tissue of the same positional origin combined without forming a boundary. The same result was obtained in combinations of Rhombomeres 3 and 5. Confrontation of tissue from even-numbered Rhombomeres 4 with 6 or 2 with 4 also failed to regenerate a boundary in the majority of cases. These results suggest that cell surface properties vary according to rhombomeric level in the hindbrain, and may support the idea of a two-segment periodicity.
Edwin Gilland - One of the best experts on this subject based on the ideXlab platform.
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Rhombomeric organization of vestibular pathways in larval frogs.
The Journal of Comparative Neurology, 2001Co-Authors: Hans Straka, Robert Baker, Edwin GillandAbstract:Rhombencephalic subnuclei and projection pathways related to vestibular function were mapped in larval ranid frogs. The retention of overt postembryonic Rhombomeres (r) allowed direct visualization of the locations of neurons retrogradely labeled with fluorescent dextran amines from the midbrain oculomotor complex, cerebellum, vestibular nuclei, and spinal cord. Oculomotor projecting vestibular neurons were mainly located in bilateral r1/2, ipsilateral r3, and contralateral r5-8, and spinal projecting vestibular neurons mainly in ipsilateral r4 and contralateral r5. Vestibular commissural neurons were located in r1-3 and r5-7 and were largely excluded from r4. Cerebellar projecting neurons included contralateral inferior olivary neurons in r8 and vestibular neurons in bilateral r6/7 and contralateral r1/2. Mapping these results onto adult anuran vestibular organization indicates that the superior vestibular nucleus derives from larval r1/2, the lateral vestibular nucleus from r3/4, and the major portions of the medial and descending vestibular nuclei from r5-8. The lateral vestibulospinal tract projects from an origin in r4, whereas a possible ascending tract of Deiters arises in r3. Rhombomere 5 contains a nuclear group that appears homologous to the tangential nucleus of fish, reptiles, and birds and thus likely serves gravistatic and linear vestibulomotor reflexes. Comparisons between frogs and other vertebrates suggest that vestibular neurons performing similar computational roles during head movements originate from the same segmental locations in different species. (C) 2001 Wiley-Liss, Inc.
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Rhombomeric organization of vestibular pathways in larval frogs.
The Journal of comparative neurology, 2001Co-Authors: Hans Straka, Robert Baker, Edwin GillandAbstract:Rhombencephalic subnuclei and projection pathways related to vestibular function were mapped in larval ranid frogs. The retention of overt postembryonic Rhombomeres (r) allowed direct visualization of the locations of neurons retrogradely labeled with fluorescent dextran amines from the midbrain oculomotor complex, cerebellum, vestibular nuclei, and spinal cord. Oculomotor projecting vestibular neurons were mainly located in bilateral r1/2, ipsilateral r3, and contralateral r5-8, and spinal projecting vestibular neurons mainly in ipsilateral r4 and contralateral r5. Vestibular commissural neurons were located in r1-3 and r5-7 and were largely excluded from r4. Cerebellar projecting neurons included contralateral inferior olivary neurons in r8 and vestibular neurons in bilateral r6/7 and contralateral r1/2. Mapping these results onto adult anuran vestibular organization indicates that the superior vestibular nucleus derives from larval r1/2, the lateral vestibular nucleus from r3/4, and the major portions of the medial and descending vestibular nuclei from r5-8. The lateral vestibulospinal tract projects from an origin in r4, whereas a possible ascending tract of Deiters arises in r3. Rhombomere 5 contains a nuclear group that appears homologous to the tangential nucleus of fish, reptiles, and birds and thus likely serves gravistatic and linear vestibulomotor reflexes. Comparisons between frogs and other vertebrates suggest that vestibular neurons performing similar computational roles during head movements originate from the same segmental locations in different species.
Manuel Mark - One of the best experts on this subject based on the ideXlab platform.
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Key roles of retinoic acid receptors alpha and beta in the patterning of the caudal hindbrain, pharyngeal arches and otocyst in the mouse.
Development (Cambridge England), 1999Co-Authors: Valérie Dupé, Norbert B. Ghyselinck, Olivia Wendling, Pierre Chambon, Manuel MarkAbstract:Mouse fetuses carrying targeted inactivations of both the RAR(a) and the RARbeta genes display a variety of malformations in structures known to be partially derived from the mesenchymal neural crest originating from post-otic Rhombomeres (e.g. thymus and great cephalic arteries) (Ghyselinck, N., Dupe, V., Dierich, A., Messaddeq, N., Garnier, J.M., Rochette-Egly, C., Chambon, P. and Mark M. (1997). Int. J. Dev. Biol. 41, 425-447). In a search for neural crest defects, we have analysed the Rhombomeres, cranial nerves and pharyngeal arches of these double null mutants at early embryonic stages. The mutant post-otic cranial nerves are disorganized, indicating that RARs are involved in the patterning of structures derived from neurogenic neural crest, even though the lack of RARalpha and RARbeta has no detectable effect on the number and migration path of neural crest cells. Interestingly, the double null mutation impairs early developmental processes known to be independent of the neural crest e.g., the initial formation of the 3rd and 4th branchial pouches and of the 3rd, 4th and 6th arch arteries. The double mutation also results in an enlargement of Rhombomere 5, which is likely to be responsible for the induction of supernumerary otic vesicles, in a disappearance of the Rhombomere 5/6 boundary, and in profound alterations of Rhombomere identities. In the mutant hindbrain, the expression domain of kreisler is twice its normal size and the caudal stripe of Krox-20 extends into the presumptive Rhombomeres 6 and 7 region. In this region, Hoxb-1 is ectopically expressed, Hoxb-3 is ectopically up-regulated and Hoxd-4 expression is abolished. These data, which indicate that retinoic acid signaling through RARalpha and/or RARbeta is essential for the specification of Rhombomere identities and for the control of caudal hindbrain segmentation by restricting the expression domains of kreisler and of Krox-20, also strongly suggest that this signaling plays a crucial role in the posteriorization of the hindbrain neurectoderm.
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In vivo functional analysis of the Hoxa-1 3′ retinoic acid response element (3′RARE)
Development (Cambridge England), 1997Co-Authors: Valérie Dupé, Pierre Chambon, Manuel Mark, P. Dolle, Marc Davenne, Jacques Brocard, Andrée Dierich, Filippo M. RijliAbstract:Retinoids are essential for normal development and both deficiency and excess of retinoic acid (RA) are teratogenic. Retinoic acid response elements (RAREs) have been identified in Hox gene promoters suggesting that endogenous retinoids may be involved in the direct control of Hox gene patterning functions. In order to test this hypothesis, we have mutated the Hoxa-1 3′RARE using the Cre-loxP targeting strategy, and studied its functional role during mouse development. We find that this enhancer plays an important role in the early establishment of the Hoxa-1 anterior expression boundary in the neural plate. This early disturbance in Hoxa-1 activation results in Rhombomere and cranial nerve abnormalities reminiscent of those obtained in the Hoxa-1 total knockout, although their severity and penetrance are lower, thus providing strong evidence for direct control of Hox gene function by retinoids during normal development. Interestingly, we also find that the Hoxa-1 expression response to RA treatment is not entirely controlled by the RARE, suggesting the existence of other retinoid-induced factors mediating the Hoxa-1 response to RA and/or the presence of additional RAREs. Interestingly, although the RARE is not required for the spatiotemporal control of colinear expression of the Hoxa genes, it is absolutely required for correct Hoxa-2 expression in Rhombomere 5.
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Two Rhombomeres are altered in Hoxa-1 mutant mice.
Development (Cambridge England), 1993Co-Authors: Manuel Mark, T Lufkin, J Vonesch, P. Dolle, Philippe Gorry, A. Lumsden, Esther Ruberte, Jean-christophe Olivo, Pierre ChambonAbstract:This study provides a detailed description of the anatomical defects in the Hoxa-1-/- mutant mice previously generated in our laboratory (T. Lufkin, A. Dierich, M. LeMeur, M. Mark and P. Chambon, 1991; Cell 66, 1105-1119). Three-dimensional reconstructions of the Hoxa-1-/- rhombencephalon reveals that it bears only five rhombomeric structures (ie. morphological segments) instead of the normal seven. The first three of these Rhombomeres appear normal as judged from the distribution pattern of CRABPI transcripts in the neurectoderm and from the histological analysis of the cranial nerve components derived from these structures. In contrast, the neural-crest-cell-free region normally located opposite Rhombomere 5 is lacking in Hoxa-1-/- embryos, and motor neurons of the facial and abducens nerves, which normally differentiate within Rhombomeres 4, 5 and 6, are missing in Hoxa-1-/- fetuses. These morphological data, combined with the determination of the molecular positional identities of the Rhombomeres 4 and 5 (P. Dolle, T. Lufkin, R. Krumlauf, M. Mark, D. Duboule and P. Chambon, 1993; Proc. Natl. Acad. Sci. USA, in press), suggest that Rhombomere 4 is markedly reduced, whereas Rhombomere 5 is almost absent. Thus, the remnants of Rhombomeres 4 and 5 appear to be fused caudally with Rhombomere 6 to form a single fourth rhombomeric structure. Moreover, the migration of neural crest cells contributing to the glossopharyngeal and vagus nerves occurs in a more rostral position, resulting in abnormalities of these cranial nerves, which were visualized by whole-mount anti-neurofilament immunostaining. The mutual relationship along the rostrocaudal axis between the otic pit and the neuroepithelial site of int-2 protein secretion (a putative otogenic cue) is not significantly changed in Hoxa-1-/- embryos. However, the abnormal relationship between the rhombencephalon and the epithelial inner ear may account for the aplasia and faulty differentiation of the membranous labyrinth, the disruption of the cartilaginous otic capsule and the disorganisation of some middle ear structures. This phenotype is compared with that of the Hoxa-1-/- mutants generated by O. Chisaka, T. S. Musci and M. R. Capecchi, 1992 (Nature 335, 516-520) and with that of the mice homozygous for the kreisler mutation.
Steven E Weicksel - One of the best experts on this subject based on the ideXlab platform.
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Targeted germ line disruptions reveal general and species-specific roles for paralog group 1 hox genes in zebrafish
BMC Developmental Biology, 2014Co-Authors: Steven E Weicksel, Ankit Gupta, Denise A Zannino, Scot A Wolfe, Charles G SagerstromAbstract:Background The developing vertebrate hindbrain is transiently segmented into Rhombomeres by a process requiring Hox activity. Hox genes control specification of Rhombomere fates, as well as the stereotypic differentiation of Rhombomere-specific neuronal populations. Accordingly, germ line disruption of the paralog group 1 (PG1) Hox genes Hoxa1 and Hoxb1 causes defects in hindbrain segmentation and neuron formation in mice. However, antisense-mediated interference with zebrafish hoxb1a and hoxb1b (analogous to murine Hoxb1 and Hoxa1 , respectively) produces phenotypes that are qualitatively and quantitatively distinct from those observed in the mouse. This suggests that PG1 Hox genes may have species-specific functions, or that anti-sense mediated interference may not completely inactivate Hox function in zebrafish. Results Using zinc finger and TALEN technologies, we disrupted hoxb1a and hoxb1b in the zebrafish germ line to establish mutant lines for each gene. We find that zebrafish hoxb1a germ line mutants have a more severe phenotype than reported for Hoxb1a antisense treatment. This phenotype is similar to that observed in Hoxb1 knock out mice, suggesting that Hoxb1/hoxb1a have the same function in both species. Zebrafish hoxb1b germ line mutants also have a more severe phenotype than reported for hoxb1b antisense treatment (e.g. in the effect on Mauthner neuron differentiation), but this phenotype differs from that observed in Hoxa1 knock out mice (e.g. in the specification of Rhombomere 5 (r5) and r6), suggesting that Hoxa1/hoxb1b have species-specific activities. We also demonstrate that Hoxb1b regulates nucleosome organization at the hoxb1a promoter and that retinoic acid acts independently of hoxb1b to activate hoxb1a expression. Conclusions We generated several novel germ line mutants for zebrafish hoxb1a and hoxb1b. Our analyses indicate that Hoxb1 and hoxb1a have comparable functions in zebrafish and mouse, suggesting a conserved function for these genes. In contrast, while Hoxa1 and hoxb1b share functions in the formation of r3 and r4, they differ with regards to r5 and r6, where Hoxa1 appears to control formation of r5, but not r6, in the mouse, whereas hoxb1b regulates formation of r6, but not r5, in zebrafish. Lastly, our data reveal independent regulation of hoxb1a expression by retinoic acid and Hoxb1b in zebrafish.
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Targeted germ line disruptions reveal general and species-specific roles for paralog group 1 hox genes in zebrafish.
BMC developmental biology, 2014Co-Authors: Steven E Weicksel, Ankit Gupta, Denise A Zannino, Scot A Wolfe, Charles G SagerstromAbstract:The developing vertebrate hindbrain is transiently segmented into Rhombomeres by a process requiring Hox activity. Hox genes control specification of Rhombomere fates, as well as the stereotypic differentiation of Rhombomere-specific neuronal populations. Accordingly, germ line disruption of the paralog group 1 (PG1) Hox genes Hoxa1 and Hoxb1 causes defects in hindbrain segmentation and neuron formation in mice. However, antisense-mediated interference with zebrafish hoxb1a and hoxb1b (analogous to murine Hoxb1 and Hoxa1, respectively) produces phenotypes that are qualitatively and quantitatively distinct from those observed in the mouse. This suggests that PG1 Hox genes may have species-specific functions, or that anti-sense mediated interference may not completely inactivate Hox function in zebrafish. Using zinc finger and TALEN technologies, we disrupted hoxb1a and hoxb1b in the zebrafish germ line to establish mutant lines for each gene. We find that zebrafish hoxb1a germ line mutants have a more severe phenotype than reported for Hoxb1a antisense treatment. This phenotype is similar to that observed in Hoxb1 knock out mice, suggesting that Hoxb1/hoxb1a have the same function in both species. Zebrafish hoxb1b germ line mutants also have a more severe phenotype than reported for hoxb1b antisense treatment (e.g. in the effect on Mauthner neuron differentiation), but this phenotype differs from that observed in Hoxa1 knock out mice (e.g. in the specification of Rhombomere 5 (r5) and r6), suggesting that Hoxa1/hoxb1b have species-specific activities. We also demonstrate that Hoxb1b regulates nucleosome organization at the hoxb1a promoter and that retinoic acid acts independently of hoxb1b to activate hoxb1a expression. We generated several novel germ line mutants for zebrafish hoxb1a and hoxb1b. Our analyses indicate that Hoxb1 and hoxb1a have comparable functions in zebrafish and mouse, suggesting a conserved function for these genes. In contrast, while Hoxa1 and hoxb1b share functions in the formation of r3 and r4, they differ with regards to r5 and r6, where Hoxa1 appears to control formation of r5, but not r6, in the mouse, whereas hoxb1b regulates formation of r6, but not r5, in zebrafish. Lastly, our data reveal independent regulation of hoxb1a expression by retinoic acid and Hoxb1b in zebrafish.