Cloning and developmental expression of a zebrafish meis2 homeobox gene

We show here that a zebrafish meis2 gene homolog has a dynamic expression pattern in the developing mesoderm and central nervous system. Meis family homeodomain proteins are known to act as cofactors with other homeodomain proteins. We find expression of meis2.1 in the developing zebrafish hindbrain and somites, correlating with reported sites of zebrafish hox gene expression, as well as in presumptive cerebellum, midbrain, retina and ventral forebrain. The expression pattern shares some, but not all, features with that of murine Meis2.     

Expression of the zinc finger Egr1 gene during zebrafish embryonic development

Egr1 is a highly conserved zinc finger protein which plays important roles in many aspects of vertebrate development and in the adult. The cDNA coding for zebrafish Egr1 was obtained and its expression pattern was examined during zebrafish embryogenesis using whole-mount in situ hybridization. Egr1 mRNA is first detected in adaxial cells in the presomitic mesoderm between 11 and 20 h post-fertilization (hpf), spanning the 4-24 somite stages. Later, Egr1 expression is observed only in specific brain areas, starting at 21 hpf and subsequently increasing in distinct domains of the central nervous system, e.g. in the telencephalon, diencephalon and hypothalamus. Between 24 and 48 hpf, Egr1 is expressed in specific domains of the hypothalamus, mesencephalon, tegmentum, pharynx, retina, otic vesicle and heart.     

Expression of the chaperonin 10 gene during zebrafish development

We have isolated a cDNA encoding chaperonin 10 (cpn10) from the zebrafish. Using northern, western, and in situ hybridization analysis, we observed that the cpn10 gene is expressed uniformly and ubiquitously throughout embryonic development of the zebrafish. Upregulation of cpn10 expression was observed following exposure of zebrafish embryos to a heat shock of 1 hour at 37 degrees C compared to control embryos raised at 27 degrees C. The extracellular form of Cpn10 called early pregnancy factor (EPF), found in the serum of pregnant mammals, was not detected in the serum of either male or female zebrafish. These expression studies suggest that Cpn10 plays a general role in zebrafish development as well as being consistent with the hypothesis that EPF is involved in the embryo implantation process in mammals.     

Expression pattern of Siaz gene during the zebrafish embryonic development

Siah is a mammalian homolog of Drosophila seven in absentia (SINA). Here we report the identification of a new member of the SINA/Siah gene family. This new gene, designated Siaz, was found in zebrafish, and its product is predicted to share extensive amino acid sequence homology with Drosophila SINA. Siaz is maternally inherited, with zygotic expression in all blastomeres starting at the mid-blastula transition. After the 20-somite stage, Siaz expression occurs in a stage-specific manner in particular regions, including the brain, eye, cranial cavity, otic vesicle, optic chiasm and gut.     

Uncoupling of neurogenesis and differentiation during retinal development

Conventionally, neuronal development is regarded to follow a stereotypic sequence of neurogenesis, migration, and differentiation. We demonstrate that this notion is not a general principle of neuronal development by documenting the timing of mitosis in relation to multiple differentiation events for bipolar cells (BCs) in the zebrafish retina using in vivo imaging. We found that BC progenitors undergo terminal neurogenic divisions while in markedly disparate stages of neuronal differentiation. Remarkably, the differentiation state of individual BC progenitors at mitosis is not arbitrary but matches the differentiation state of post-mitotic BCs in their surround. By experimentally shifting the relative timing of progenitor division and differentiation, we provide evidence that neurogenesis and differentiation can occur independently of each other. We propose that the uncoupling of neurogenesis and differentiation could provide neurogenic programs with flexibility, while allowing for synchronous neuronal development within a continuously expanding cell pool.     

Expression of Chx10 and Chx10-1 in the developing chicken retina

We have isolated full-length cDNAs of chick Chx10 and Chx10-1, two members of the paired type homeobox/CVC gene family. A comparison of sequences suggests that Chx10 is closely related to Alx/Vsx-2 and Vsx-2 of zebrafish and goldfish, respectively; while Chx10-1 is closely related to Vsx-1 of zebrafish and goldfish. Chx10 and Chx10-1 are expressed in the early retinal neuroepithelium, but not in the pigment epithelium and lens. The expression of Chx10 is present in most retinal neuroblasts, while Chx10-1 exhibits a novel pattern along the nasotemporal border. In the differentiating retina, both Chx10 and Chx10-1 are restricted to bipolar cells and are maintained at a low level in bipolar cells of the mature retina.     

Dmbx1, a novel evolutionarily conserved paired-like homeobox gene expressed in the brain of mouse embryos.

To identify novel homeobox genes expressed during mouse embryogenesis, we searched the databases and found a novel mouse paired-like homeobox gene, Dmbx1(diencephalon/mesencephalon-expressed brain homeobox gene 1), that is also conserved in zebrafish and human. Linkage analysis mapped mouse Dmbx1 to the mid-portion of chromosome 4 that is the homologous gene cluster region of human chromosome 1, where human DMBX1 is located. Both mouse and human Dmbx1/DMBX1 have four coding exons and their gene structures are conserved. Whole-mount in situ hybridization revealed that Dmbx1 expression is detected in 7.5-9.5 dpc mouse embryos. At 7.5 and 8.5 dpc, Dmbx1 is expressed in a sub-region of the anterior head folds. At 9.5 dpc, expression is observed in the caudal diencephalon as well as in the mesencephalon and is restricted to the neuroepithelium. Expression in adult tissues was detected in brain, stomach, and testis. Dmbx1 provides a unique marker of the developing anterior nervous system and should provide a useful molecular resource to elucidate the mechanisms that pattern the vertebrate brain.     

Capitella sp. I homeobrain-like, the first lophotrochozoan member of a novel paired-like homeobox gene family

The paired-like class of homeobox genes contains numerous distinct families, many of which have been implicated in a variety of developmental functions. We report the isolation and expression of a gene with high similarity to Drosophila melanogaster homeobrain from the polychaete annelid Capitella sp. I. The homeobrain-like (hbnl) gene is a paired-like gene that contains a conserved homeodomain, octapeptide region, alanine stretches, and an OAR domain. Gene orthology analyses of the homeodomain from CapI-hbnl places this gene in a new family of paired-like homeodomain genes that includes D. melanogaster homeobrain (hbn) and representatives from all major bilaterian clades as well as a cnidarian gene. CapI-hbnl expression is largely restricted to subsets of cells in the brain and eyes during larval development in Capitella sp. I. The earliest expression of CapI-hbnl is in small discrete cell clusters in the cerebral ganglia. This expression persists through late larval developmental stages whereas expression is absent in postmetamorphic juveniles. Outside the brain, expression is present on the ventral side of the larva in two small cell clusters, at the brain/pharyngeal border and in the anterior-most segment. CapI-hbnl shares features of brain expression with hbn, although in contrast to hbn, which is expressed along the length of the ventral nerve cord, CapI-hbnl has a restricted anterior expression pattern. CapI-hbnl represents an important neural marker for characterization of the annelid nervous system.     

Expression of Chx10 and Chx10-1 in the developing chicken retina

We have isolated full-length cDNAs of chick Chx10 and Chx10-1, two members of the paired type homeobox/CVC gene family. A comparison of sequences suggests that Chx10 is closely related to Alx/Vsx-2 and Vsx-2 of zebrafish and goldfish, respectively; while Chx10-1 is closely related to Vsx-1 of zebrafish and goldfish. Chx10 and Chx10-1 are expressed in the early retinal neuroepithelium, but not in the pigment epithelium and lens. The expression of Chx10 is present in most retinal neuroblasts, while Chx10-1 exhibits a novel pattern along the nasotemporal border. In the differentiating retina, both Chx10 and Chx10-1 are restricted to bipolar cells and are maintained at a low level in bipolar cells of the mature retina.