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At least 1,621 records · Page 90Linked to original sources
PubMed2006

Molecular signaling in feather morphogenesis.

The development and regeneration of feathers have gained much attention recently because of progress in the following areas. First, pattern formation. The exquisite spatial arrangement provides a simple model for decoding the rules of morphogenesis. Second, stem cell biology. In every molting, a few stem cells have to rebuild the entire epithelial organ, providing much to learn on how to regenerate an organ physiologically. Third, evolution and development ('Evo-Devo'). The discovery of feathered dinosaur fossils in China prompted enthusiastic inquiries about the origin and evolution of feathers. Progress has been made in elucidating feather morphogenesis in five successive phases: macro-patterning, micro-patterning, intra-bud morphogenesis, follicle morphogenesis and regenerative cycling.

Animals↗
PubMed2004

Analysis of cCx39 expression pattern during chick development.

The present study reports the expression pattern of connexin39 (cCx39) in chick embryos at different stages of central nervous system development. We examined the expression between HH17 and HH40 developmental stages of chicken embryos by in situ hybridization (ISH) technique. Connexin39 was first expressed at HH17. It stained neuroepithelial cells in the optic (OV) and telencephalic (TEL) vesicles, plus in the superficial mesenchyme of the two rostral branchial arches (maxilar and mandibular). These cells probably originated from the neural crest. This expression pattern changed drastically between stages HH17 and HH23, while it showed relatively little modifications from HH23 to HH29. At these times, connexin39 was expressed in three regions: the telencephalic vesicle, the diencephalon and the isthmus. At later stages, HH35 and HH40, connexin39 was mainly expressed in the ventricular epithelium and three cell layers of the stratum griseum and fibrosum superficialis (SGFS) in the optic tectum, as well as in granular and nuclear cells in the cerebellum. In conclusion, the expression pattern of connexin39 in embryonic nervous system is dynamic. This pattern is different from, and in some aspects complementary to, those showed by other connexins during brain development.

Animals↗
PubMed2003

The Drm-Bowl-Lin relief-of-repression hierarchy controls fore- and hindgut patterning and morphogenesis.

The elucidation of pathways linking patterning to morphogenesis is a problem of great interest. We show here that, in addition to their roles in patterning and morphogenesis of the hindgut, the Drosophila genes drumstick (drm) and bowl are required in the foregut for spatially localized gene expression and the morphogenetic processes that form the proventriculus. drm and bowl belong to a family of genes encoding C(2)H(2) zinc finger proteins; the other two members of this family are odd-skipped (odd) and sob. In both the fore- and hindgut, drm acts upstream of lines (lin), which encodes a putative transcriptional regulator, and relieves its repressive function. In spite of its phenotypic similarities with drm, bowl was found in both foregut and hindgut to act downstream, rather than upstream, of lin. These results support a hierarchy in which Drm relieves the repressive effect of Lin on Bowl, and Bowl then acts to promote spatially localized expression of genes (particularly the JAK/STAT pathway ligand encoded by upd) that control fore- and hindgut morphogenesis. Since the odd-family and lin are conserved in mosquito, mouse, and humans, we propose that the odd-family genes and lin may also interact to control patterning and morphogenesis in other insects and in vertebrates.

Animals↗
PubMed2004

Endothelin-1 regulates the dorsoventral branchial arch patterning in mice.

Endothelin-1 (ET-1), a 21-amino acid peptide secreted by the epithelium and core mesenchyme in the branchial arches as well as vascular endothelium, is involved in craniofacial and cardiovascular development through endothelin receptor type-A (EdnrA) expressed in the neural crest-derived ectomesenchyme. Here we show that ET-1(-/-) mutant mice exhibit a homeotic-like transformation of the lower jaw to an upper jaw. Most of the maxillary arch-derived components are duplicated and replaced mandibular arch-derived structures, resulting in a mirror image of the upper and lower jaws in the ET-1(-/-) mutant. As for hyoid arch-derivatives, the ventral structures are severely affected in comparison to the dorsal ones in the ET-1(-/-) mutant. Correspondingly, the expression of Dlx5 and Dlx6, Distalless-related homeobox genes determining the ventral identity of the anterior branchial arches, and of the mandibular marker gene Pitx1 is significantly downregulated in the ET-1(-/-) mutant, whereas the expression of Dlx2 and the maxillary marker gene Prx2 is unaffected or rather upregulated. These findings indicate that the ET-1/EdnrA signaling may contribute to the dorsoventral axis patterning of the branchial arch system as a mediator of the regional intercellular interactions.

Animals↗
PubMed2004

Differences in expression pattern and function between zebrafish hoxc13 orthologs: recruitment of Hoxc13b into an early embryonic role.

Vertebrate Hox genes are generally believed to initiate expression at the primitive streak or early neural plate stages. The timing and spatial restrictions of the Hox expression patterns during these stages correlate well with their demonstrated role in axial patterning. Here we demonstrate that one zebrafish hoxc13 ortholog, hoxc13a, has an expression pattern in the developing tail bud that is consistent with the gene playing a role in axial patterning. However, the second hoxc13 ortholog, hoxc13b, is maternally expressed and is detectable in every cell of early cleavage embryos through gastrulae. In addition, both transcript and protein are detectable at these stages. At 19 h post fertilization (hpf), hoxc13b expression is up-regulated in the tail bud, becoming restricted to the tail bud by 24 hpf. Importantly, by 24 hpf, hoxc13b morphants show a specific developmental delay, which can be rescued by co-injecting synthetic capped hoxc13a or hoxc13b message. These data suggest some functional divergence due to altered expression patterns of the two hoxc13 orthologs after duplication. Further characterization of the hoxc13b morphant delay reveals that it is biphasic in nature, with the first phase of the delay occurring before gastrulation, suggesting a new role for vertebrate Hox genes before their conserved role in axial patterning. The extent of the delay does not change through 20 hpf; however, an additional delay emerges at this time. Notably, this second phase of the delay correlates with hoxc13b expression pattern becoming restricted to the tail bud.

Amino Acid Sequence↗
PubMed2005

A critical role of teashirt for patterning the ventral epidermis is masked by ectopic expression of tiptop, a paralog of teashirt in Drosophila.

The teashirt gene encodes a protein with three widely spaced zinc finger motifs that is crucial for specifying trunk identity in Drosophila embryos. Here, we describe a gene called tiptop, which encodes a protein highly similar to Teashirt. We have analyzed the expression patterns and functions of these two genes in the trunk of the embryo. Initially, teashirt and tiptop expressions are detected in distinct domains; teashirt in the trunk and tiptop in parts of the head and tail. In different mutant situations, we show that, in the trunk and head, they repress each other's expression. Unlike teashirt, we found that deletion of tiptop is homozygous viable and fertile. However, embryos lacking both gene activities display a more severe trunk phenotype than teashirt mutant embryos alone. Ectopic expression of either gene produces an almost identical phenotype, indicating that Teashirt and Tiptop have, on the whole, common activities. We conclude that Teashirt and Tiptop repress each other's expression and that Teashirt has a crucial role for trunk patterning that is in part masked by ectopic expression of Tiptop.

Amino Acid Sequence↗
PubMed1998

Spatially restricted expression of pipe in the Drosophila egg chamber defines embryonic dorsal-ventral polarity.

Expression of pipe in the somatic tissue of the Drosophila ovary is required for the formation of embryonic dorsal-ventral polarity. pipe, which encodes an enzyme similar to the glycosaminoglycan-modifying enzyme heparan sulfate 2-O-sulfotransferase, is expressed in a spatially restricted domain of follicle cells on the ventral side of the egg chamber. Mutations that affect follicular polarity correspondingly alter the spatial pattern of pipe expression. Directed expression of pipe in otherwise pipe mutant females restores embryonic lateral and ventral pattern elements and can orient the dorsal-ventral axis of the embryo. Thus, the localized expression of pipe and the spatially restricted modification of carbohydrate chains play pivotal roles in the mechanisms that establish embryonic pattern and integrate follicular and embryonic polarity.

5' Untranslated Regions↗
PubMed2002

Hedgehog patterns midbrain ARChitecture.

Recent work from Agarwala et al. has uncovered exquisite ventral patterning in the mesencephalon. Using electroporation in chicks, they show that ectopic expression of Sonic Hedgehog (Shh) in dorsal mesencephalon can recapitulate this patterning in its entirety. These results are discussed in the context of the purported role of Shh as a morphogen.

Animals↗
PubMed2000

Zebrafish Dkk1, induced by the pre-MBT Wnt signaling, is secreted from the prechordal plate and patterns the anterior neural plate.

mRNA injection into the ventral blastomeres of Xenopus embryos of mRNA encoding Wnt pathway genes induces a secondary axis with complete head structures. To identify target genes of the pre-MBT dorsalization pathway that might be responsible for head formation in zebrafish, we have cloned zebrafish dickkopf1 (dkk1), which is expressed in tissues implicated in head patterning. We found that dkk1 blocks the post-MBT Wnt signaling and dkk1 is a target of the pre-MBT Wnt signaling. Dkk1 overexpression in the prechordal plate suggests that Dkk1, secreted from the prechordal plate, expands the forebrain at the expense of the midbrain in the anterior neural plate. Furthermore, dkk1 acts in parallel to the homeobox gene bozozok and bozozok is required for the maintenance of dkk1 expression. The nodal gene squint is also required for the maintenance of dkk1 expression. Among the mutually dependent target genes of the pre-MBT Wnt signaling, dkk1 plays an important role in patterning the anterior head of zebrafish.

Amino Acid Sequence↗
PubMed2001

Differential gene expression of Xenopus Pitx1, Pitx2b and Pitx2c during cement gland, stomodeum and pituitary development.

The members of the Pitx family of homeobox transcription factors have been involved in many aspects of vertebrate embryogenesis, like for example, development of teeth, eyes and limbs. We previously reported expression patterns and function of Pitx2c in the generation of laterality and asymmetric morphogenesis of heart and gastro-intestinal tract in mouse, frog and zebrafish (Development 126 (1999) 1225; Mech. Dev. 90 (2000) 41). Here we describe the differential expression of Pitx1, Pitx2b and Pitx2c during anterior ectodermal pattern formation and differentiation of cement gland, stomodeum and pituitary in the frog Xenopus laevis.

Amino Acid Sequence↗
PubMed2000

Expression of chick BMP-1/Tolloid during patterning of the neural tube and somites.

The expression pattern described here is that of the chick BMP-1/Tolloid family of secreted metalloproteinases during early stages of development. BMP-1/Tolloid transcripts are expressed in the blastoderm, at gastrulation stages and as the neural plate forms and neural tube folds, BMP-1/Tolloid is found at the neural plate/ectodermal transition. Expression is maintained in the premigratory neural crest, and transiently in the migrating cephalic neural crest cells. BMP-1/Tolloid is also expressed in the caudal, but not in the anterior notochord, and in the ventral neural tube at the time of dorso-ventral patterning. Further sites of BMP-1/Tolloid expression are the lateral plate mesoderm and the dermotome and the myotome of the somites.

Animals↗
PubMed2001

Zebrafish wnt8 encodes two wnt8 proteins on a bicistronic transcript and is required for mesoderm and neurectoderm patterning.

In vertebrates, wnt8 has been implicated in the early patterning of the mesoderm. To determine directly the embryonic requirements for wnt8, we generated a chromosomal deficiency in zebrafish that removes the bicistronic wnt8 locus. We report that homozygous mutants exhibit pronounced defects in dorso-ventral mesoderm patterning and in the antero-posterior neural pattern. Despite differences in their signaling activities, either coding region of the bicistronic RNA can rescue the deficiency phenotype. Specific interference of wnt8 translation by morpholino antisense oligomers phenocopies the deficiency, and interference with wnt8 translation in ntl and spt mutants produces embryos lacking trunk and tail. These data demonstrate that the zebrafish wnt8 locus is required during gastrulation to pattern both the mesoderm and the neural ectoderm properly.

Amino Acid Sequence↗
PubMed2001

The retinoic acid-inactivating enzyme CYP26 is essential for establishing an uneven distribution of retinoic acid along the anterio-posterior axis within the mouse embryo.

Retinoic acid (RA), a derivative of vitamin A, plays a pivotal role in vertebrate development. The level of RA may be determined by the balance between its synthesis and degradation. We have examined the role of CYP26, a P450 enzyme that may degrade RA, by generating mutant mice that lack CYP26. CYP26(-/-) mice exhibited anomalies, including caudal agenesis, similar to those induced by administration of excess RA. The concentration of endogenous RA, as revealed by marker gene activity, was markedly increased in the tailbud of the mutant animals, in which CYP26 is normally expressed. Expression of T (Brachyury) and Wnt3a in the tailbud was down-regulated in CYP26(-/-) mice, which may underlie the caudal truncation. The lack of CYP26 also resulted in homeotic transformation of vertebrae as well as in misspecification of the rostral hindbrain associated with anterior expansion of RA-positive domains. These results suggest that local degradation of RA by CYP26 is required for establishing an uneven distribution of RA along the anterio-posterior axis, which is essential for patterning the hindbrain, vertebrae, and tailbud.

Animals↗
PubMed1996

Micrometer resolution silane-based patterning of hippocampal neurons: critical variables in photoresist and laser ablation processes for substrate fabrication.

Toward the goal of creating patterns of primary hippocampal neurons in low density culture, we investigated techniques to fabricate microminiature grids of organofunctional silanes on glassy surfaces. A new photoresist (PR) process, Selective Silane Removal (SSR), was developed and compared to two previously developed techniques which use PR and laser patterning. The grid patterns consisted of 27 combinations of path width, length, and intersection (node diameter). The background consisted of squares bounded by the paths. The best neuron patterning was observed on substrates produced by the SSR process where cytophilic aminosilane is uniformly deposited and selectively removed from the background. Controlling water during aminosilane deposition was critical to good neuronal growth and patterning. Oxygen plasma etching of background regions prior to cytophobic phenylsilane binding significantly reduced off-pattern cell growth. Up to 90% of somata grown on these substrates complied to the pattern, and an average of 77% of background regions were free of neurites or cells connected to the pattern. The highest laser energy density, 120 mJ/cm2, produced the best compliance on lased substrates, with an average of 35% of background regions free of connected cells and neurites, but considerable variation across the surface. On substrates with excellent patterning, compliance to nodes was found to be dependent on pattern dimensions, with 20-micron node diameters and 80-micron internodal path lengths increasing compliance.

Animals↗
PubMed2007

Left-right dynein motor implicated in selective chromatid segregation in mouse cells.

During cell division, copies of mouse chromosome 7 are segregated selectively or randomly to daughter cells depending on the cell type. The mechanism for differential segregation is unknown. Because mouse left-right dynein (LRD) gene mutations result in randomization of visceral organs' laterality, we hypothesized that LRD may also function in selective chromatid segregation. Indeed, upon knock-down by RNA interference methods, LRD depletion disrupts biased segregation. LRD messenger RNA presence or absence correlates with the observed segregation patterns. This work supports the claim that LRD functions in a mechanism for selective chromatid segregation.

Animals↗
PubMed2004

Role of Hand1/eHAND in the dorso-ventral patterning and interventricular septum formation in the embryonic heart.

Molecular mechanisms for the dorso-ventral patterning and interventricular septum formation in the embryonic heart are unknown. To investigate a role of Hand1/eHAND in cardiac chamber formation, we generated Hand1/eHAND knock-in mice where Hand1/eHAND cDNA was placed under the control of the MLC2V promoter. In Hand1/eHAND knock-in mice, the outer curvature of the right and left ventricles expanded more markedly. Moreover, there was no interventricular groove or septum formation, although molecularly, Hand1/eHAND knock-in hearts had two ventricles. However, the morphology of the inner curvature of the ventricles, the atrioventricular canal, and the outflow tract was not affected by Hand1/eHAND expression. Furthermore, expression of Hand1/eHAND in the whole ventricles altered the expression patterns of Chisel, ANF, and Hand2/dHAND but did not affect Tbx5 expression. In contrast, the interventricular septum formed normally in transgenic embryos overexpressing Hand1/eHAND in the right ventricle but not in the boundary region. These results suggested that Hand1/eHAND is involved in expansion of the ventricular walls and that absence of Hand1/eHAND expression in the boundary region between the right and left ventricles may be critical in the proper formation of the interventricular groove and septum. Furthermore, Hand1/eHAND is not a master regulatory gene that specifies the left ventricle myocyte lineage but may control the dorso-ventral patterning in concert with additional genes.

Animals↗
PubMed2003

Ogon/Secreted Frizzled functions as a negative feedback regulator of Bmp signaling.

The zebrafish mutant ogon (also called mercedes and short tail) displays ventralized phenotypes similar to the chordino (dino) mutant, in which the gene for the Bmp antagonist Chordin is mutated. We isolated the gene responsible for ogon by a positional cloning strategy and found that the ogon locus encodes a zebrafish homolog of Secreted Frizzled (Sizzled), which has sequence similarity to a Wnt receptor, Frizzled. Unlike other secreted Frizzled-related proteins (sFrps) and the Wnt inhibitor Dickkopf1, the misexpression of Ogon/Sizzled dorsalized, but did not anteriorize, the embryos, suggesting a role for Ogon/Sizzled in Bmp inhibition. Ogon/Sizzled did not inhibit a Wnt8-dependent transcription in the zebrafish embryo. ogon/sizzled was expressed on the ventral side from the late blastula through the gastrula stages. The ventral ogon/sizzled expression in the gastrula stage was reduced or absent in the swirl/bmp2b mutants but expanded in the chordino mutants. Misexpression of ogon/sizzled did not dorsalize the chordino mutants, suggesting that Ogon/Sizzled required Chordin protein for dorsalization and Bmp inhibition. These data indicate that Ogon/Sizzled functions as a negative regulator of Bmp signaling and reveal a novel role for a sFrp in dorsoventral patterning.

Amino Acid Sequence↗