Search

Although the human tail is completely absent at birth, the embryonic tail is formed just as in other tailed amniotes. Since all morphological variations are created from variations in developmental processes, elucidation of the tail reduction process during embryonic development may be necessary to clarify the human evolutionary process. The tail has also been of great interest to the medical community....

Although the human tail is completely absent at birth, the embryonic tail is formed just as in other tailed amniotes. Since all morphological variations are created from variations in developmental processes, elucidation of the tail reduction process during embryonic development may be necessary to clarify the human evolutionary process. The tail has also been of great interest to the medical community....

Development consists of complex morphogenetic movements that shape individual tissues as well as the embryo. Tissues must interact both physically and through signaling molecules to coordinate the formation of various organs and the entire body plan. My thesis work sought to characterize tissue interactions that govern muscle formation during vertebrate embryo development using the African clawed frog Xenopus laevis as a model system. Chapter 1 of this dissertation provides a general introduction to the morphogenetic events and molecular regulation leading to muscle formation. Chapter 2 presents two previously-undiscovered morphogenetic phenomena involving the muscle tissue as well as individual muscle fibers. My experiments confirmed the function and mechanisms of muscle tissue unfolding as well as the cell rearrangements that ultimately place muscle fibers into organized arrays for proper functioning. Chapter 3 summarizes my work to further analyze a previously-unreported reciprocal relationship between the neural tissue and the prospective muscle tissue. My work shows that the neural plate influences the size of the underlying muscle. Enlarging the neural plate results in a corresponding increase in the size of the muscle tissue. Here, I dissect the source and fate of ectopic muscle tissue and determine the effect of tissue size on muscle morphogenesis. As a whole, this work summarizes my research to characterize the molecular and morphological events necessary for proper muscle formation during embryo development.

The ADAMTS5 metzincin, a secreted zinc-dependent metalloproteinase, modulates the extracellular matrix (ECM) during limb morphogenesis and other developmental processes. Here, the role of ADAMTS5 was investigated by knockdown of zebrafish adamts5 during embryogenesis. This revealed impaired Sonic Hedgehog (Shh) signaling during somite patterning and early myogenesis. Notably, synergistic regulation of myod expression by ADAMTS5 and Shh during somite differentiation was observed. These roles were not dependent upon the catalytic activity of ADAMTS5. These data identify a non-enzymatic function for ADAMTS5 in regulating an important cell signaling pathway that impacts on muscle development, with implications for musculoskeletal diseases in which ADAMTS5 and Shh have been associated.

Development consists of complex morphogenetic movements that shape individual tissues as well as the embryo. Tissues must interact both physically and through signaling molecules to coordinate the formation of various organs and the entire body plan. My thesis work sought to characterize tissue interactions that govern muscle formation during vertebrate embryo development using the African clawed frog Xenopus laevis as a model system. Chapter 1 of this dissertation provides a general introduction to the morphogenetic events and molecular regulation leading to muscle formation. Chapter 2 presents two previously-undiscovered morphogenetic phenomena involving the muscle tissue as well as individual muscle fibers. My experiments confirmed the function and mechanisms of muscle tissue unfolding as well as the cell rearrangements that ultimately place muscle fibers into organized arrays for proper functioning. Chapter 3 summarizes my work to further analyze a previously-unreported reciprocal relationship between the neural tissue and the prospective muscle tissue. My work shows that the neural plate influences the size of the underlying muscle. Enlarging the neural plate results in a corresponding increase in the size of the muscle tissue. Here, I dissect the source and fate of ectopic muscle tissue and determine the effect of tissue size on muscle morphogenesis. As a whole, this work summarizes my research to characterize the molecular and morphological events necessary for proper muscle formation during embryo development.

Segmentation defects of the vertebrae (SDV) are caused by aberrant somite formation during embryogenesis and result in irregular formation of the vertebrae and ribs. The Notch signal transduction pathway plays a critical role in somite formation and patterning in model vertebrates. In humans, mutations in several genes involved in the Notch pathway are associated with SDV, with both autosomal recessive (MESP2, DLL3, LFNG, HES7) and autosomal dominant (TBX6) inheritance. However, many individuals with SDV do not carry mutations in these genes. Using whole-exome capture and massive parallel sequencing, we identified compound heterozygous mutations in RIPPLY2 in two brothers with multiple regional SDV, with appropriate familial segregation. One novel mutation (c.A238T:p.Arg80*) introduces a premature stop codon. In transiently transfected C2C12 mouse myoblasts, the RIPPLY2 mutant protein demonstrated impaired transcriptional repression activity compared with wild-type RIPPLY2 despite similar levels of expression. The other mutation (c.240-4T>G), with minor allele frequency <0.002, lies in the highly conserved splice site consensus sequence 5' to the terminal exon. Ripply2 has a well-established role in somitogenesis and vertebral column formation, interacting at both gene and protein levels with SDV-associated Mesp2 and Tbx6. We conclude that compound heterozygous mutations in RIPPLY2 are associated with SDV, a new gene for this condition.

The problems of sustaining placenta formation in embryos produced by nuclear transfer have emphasized the need for basic knowledge about epiblast formation and gastrulation in bovine embryos. The aims of this study were to define stages of bovine post-hatching embryonic development and to analyse functional mechanisms of germ-layer formation. Embryos developed in vivo were collected after slaughter from superovulated cows on days 9, 11, 14 and 21 after insemination and processed for transmission electron microscopy (n = 26) or immunohistochemistry (n = 27) for potential germ-layer characterization (cytokeratin 8 for potential ectoderm; alpha-1-fetoprotein for potential endoderm; and vimentin for potential mesoderm). On day 9, the embryos were devoid of zona pellucida and presented a well-defined inner cell mass (ICM), which was covered by a thin layer of trophoblast cells (the Rauber's layer). Formation of the hypoblast from the inside of the ICM was ongoing. On day 11, the Rauber's layer was focally interrupted and adjacent underlying ICM cells formed tight junctions. The hypoblast, which formed a thin confluent cell layer, was separated from the ICM and the trophoblast by intercellular matrix. The embryos were ovoid to tubular and displayed a confluent hypoblast on day 14. The epiblast was inserted into the trophoblast epithelium and tight junctions and desmosomes were present between adjacent epiblast cells as well as between peripheral epiblast and trophoblast cells. In some embryos, the epiblast was more or less covered by foldings of trophoblast in the process of forming the amniotic cavity. Cytokeratin 8 was localized to the trophoblast and the hypoblast underlying the epiblast; alpha-1-fetoprotein was localized to most hypoblast cells underlying the trophoblast; and vimentin was localized to most epiblast cells. On day 21, the smallest embryos displayed a primitive streak and formation of the neural groove, whereas the largest embryos presented a neural tube

Sox9 is expressed at the onset of the genital ridge formation in both sexes. It is assumed that Sry, the testis determining gene, turns Sox9 on in male embryos because it is turned off in female embryos. Spatial expression of Sry follows a cranio-caudal pattern. Here, we asked if Sox9 is expressed in the same cell lineage and with a similar pattern as Sry. A correlative study between the structural changes in the genital ridge and the immunocytochemical localization of Sox9-positive cells was undertaken. We used a transgenic strain expressing the green fluorescent protein (GFP) that considerably enhanced the cell context where the first Sox9-positive cells appear. Although Sox9-positive cells are located among loose mesenchymal cells by stages of 8-14 tail somites (ts) in both sexes, they are absent in the thickening coelomic epithelium of females. At 15 ts the first Sox9-positive cells appear within the core of the condensed cells only in male genital ridges. At 17 ts, a gradient of Sox9-positive cells in males is apparent, closely following the cranio-caudal pattern of cell aggregation seen in genital ridges of both sexes. Hence, our results suggest that Sox9 is expressed only in loose mesenchymal cells in both sexes and that expression of Sox9 in males requires the prior aggregation of cells in the genital ridges. The correspondence of Sox9 and Sry pattern of expression supports that both genes are expressed in the preSertoli cell lineage in the core of the genital ridges. Copyright © 2003 S. Karger AG, Basel.

Desrt is a mouse gene of the AT-rich interaction domain family of transcription factors. Here we describe the temporal and spatial pattern of expression of Desrt during mouse organogenesis. Desrt expression is first detected in the intermediate plate mesoderm, providing an early embryonic marker for this tissue, and subsequently in the nephrogenic cords of the urogenital ridges. A highly dynamic expression pattern is observed in the developing limb, implicating Desrt in limb patterning. Desrt is also detected in the myotome of the somites, the oro-naso-pharyngeal ectoderm and underlying mesenchyme, otic vesicles, the gut and its derivatives, and transiently in the liver. Copyright © 2001 Elsevier Science Ireland Ltd.

The problems of sustaining placenta formation in embryos produced by nuclear transfer have emphasized the need for basic knowledge about epiblast formation and gastrulation in bovine embryos. The aims of this study were to define stages of bovine post-hatching embryonic development and to analyse functional mechanisms of germ-layer formation. Embryos developed in vivo were collected after slaughter from superovulated cows on days 9, 11, 14 and 21 after insemination and processed for transmission electron microscopy (n = 26) or immunohistochemistry (n = 27) for potential germ-layer characterization (cytokeratin 8 for potential ectoderm; alpha-1-fetoprotein for potential endoderm; and vimentin for potential mesoderm). On day 9, the embryos were devoid of zona pellucida and presented a well-defined inner cell mass (ICM), which was covered by a thin layer of trophoblast cells (the Rauber's layer). Formation of the hypoblast from the inside of the ICM was ongoing. On day 11, the Rauber's layer was focally interrupted and adjacent underlying ICM cells formed tight junctions. The hypoblast, which formed a thin confluent cell layer, was separated from the ICM and the trophoblast by intercellular matrix. The embryos were ovoid to tubular and displayed a confluent hypoblast on day 14. The epiblast was inserted into the trophoblast epithelium and tight junctions and desmosomes were present between adjacent epiblast cells as well as between peripheral epiblast and trophoblast cells. In some embryos, the epiblast was more or less covered by foldings of trophoblast in the process of forming the amniotic cavity. Cytokeratin 8 was localized to the trophoblast and the hypoblast underlying the epiblast; alpha-1-fetoprotein was localized to most hypoblast cells underlying the trophoblast; and vimentin was localized to most epiblast cells. On day 21, the smallest embryos displayed a primitive streak and formation of the neural groove, whereas the largest embryos presented a neural tube

Desrt is a mouse gene of the AT-rich interaction domain family of transcription factors. Here we describe the temporal and spatial pattern of expression of Desrt during mouse organogenesis. Desrt expression is first detected in the intermediate plate mesoderm, providing an early embryonic marker for this tissue, and subsequently in the nephrogenic cords of the urogenital ridges. A highly dynamic expression pattern is observed in the developing limb, implicating Desrt in limb patterning. Desrt is also detected in the myotome of the somites, the oro-naso-pharyngeal ectoderm and underlying mesenchyme, otic vesicles, the gut and its derivatives, and transiently in the liver. Copyright © 2001 Elsevier Science Ireland Ltd.

Sox9 is expressed at the onset of the genital ridge formation in both sexes. It is assumed that Sry, the testis determining gene, turns Sox9 on in male embryos because it is turned off in female embryos. Spatial expression of Sry follows a cranio-caudal pattern. Here, we asked if Sox9 is expressed in the same cell lineage and with a similar pattern as Sry. A correlative study between the structural changes in the genital ridge and the immunocytochemical localization of Sox9-positive cells was undertaken. We used a transgenic strain expressing the green fluorescent protein (GFP) that considerably enhanced the cell context where the first Sox9-positive cells appear. Although Sox9-positive cells are located among loose mesenchymal cells by stages of 8-14 tail somites (ts) in both sexes, they are absent in the thickening coelomic epithelium of females. At 15 ts the first Sox9-positive cells appear within the core of the condensed cells only in male genital ridges. At 17 ts, a gradient of Sox9-positive cells in males is apparent, closely following the cranio-caudal pattern of cell aggregation seen in genital ridges of both sexes. Hence, our results suggest that Sox9 is expressed only in loose mesenchymal cells in both sexes and that expression of Sox9 in males requires the prior aggregation of cells in the genital ridges. The correspondence of Sox9 and Sry pattern of expression supports that both genes are expressed in the preSertoli cell lineage in the core of the genital ridges. Copyright © 2003 S. Karger AG, Basel.

[no abstract]

The transcriptional regulation of the Mrf4/Myf5 locus depends on a multitude of enhancers that, in equilibria with transcription balancing sequences and the promoters, regulate the expression of the two genes throughout embryonic development and in the adult. Transcription in a particular set of muscle progenitors can be driven by the combined outputs of several enhancers that are not able to recapitulate the entire expression pattern in isolation, or by the action of a single enhancer the activity of which in isolation is equivalent to that within the context of the locus. We identified a new enhancer element of this second class, ECR111, which is highly conserved in all vertebrate species and is necessary and sufficient to drive Myf5 expression in ventro-caudal and ventro-rostral somitic compartments in the mouse embryo. EMSA analyses and data obtained from binding-site mutations in transgenic embryos show that a binding site for a TEA Domain (TEAD) transcription factor is essential for the function of this new enhancer, while ChIP assays show that at least two members of the family of transcription factors bind to it in vivo.

During vertebrate embryonic development, somites are formed from the unsegmented presomitic mesoderm (PSM) by a highly regulated process. They are formed in pairs in an anterior to posterior progression on either side of the notochord. Ca2+ signals, in the form of localized elevations of [Ca2+]i were visualized from three separate embryological domains during somitogenesis: the notochord, PSM and maturing somites. Unlike the ordered morphological process of somitogenesis, Ca2+ signals were found to be chaotic with respect to time and location within individual embryos, and when comparing embryos. They did, however, display common characteristics that provided clues to their embryological function and significance. Signals generated by the maturing somites took the form of intercellular Ca2+ waves generated by Ca2+ release from the ER via IP3Rs. They occurred predominantly at the medial or lateral extremities of maturing somites and evidence, resulting from manipulation of [Ca2+]i, indicates that they may play a role in establishing and maintaining these essential boundaries. Signals visualized from the PSM were also stochastic with respect to location and time, and again took the form of localized intercellular Ca2+ waves generated by Ca2+ release via IP3Rs. They were predominantly generated in a region of the PSM that displayed some correlation with the expression pattern of the zebrafish homologue (her1) of the Drosophila pair-rule gene Hairy, which is involved in generating periodicity during somitogenesis and has been suggested to be linked to Ca2+ signaling. Experimentation indicated, however, that there appeared to be no linkage between the PSM Ca2+ transients visualized and her1 expression patterns. Signals generated by the notochord were also chaotic and generated by Ca2+ release via IP3Rs. Their biological function remains unclear. It is thus suggested that the transients generated by these three embryological domains represent a new class of stochastic dev

[no abstract]

During vertebrate embryonic development, somites are formed from the unsegmented presomitic mesoderm (PSM) by a highly regulated process. They are formed in pairs in an anterior to posterior progression on either side of the notochord. Ca2+ signals, in the form of localized elevations of [Ca2+]i were visualized from three separate embryological domains during somitogenesis: the notochord, PSM and maturing somites. Unlike the ordered morphological process of somitogenesis, Ca2+ signals were found to be chaotic with respect to time and location within individual embryos, and when comparing embryos. They did, however, display common characteristics that provided clues to their embryological function and significance. Signals generated by the maturing somites took the form of intercellular Ca2+ waves generated by Ca2+ release from the ER via IP3Rs. They occurred predominantly at the medial or lateral extremities of maturing somites and evidence, resulting from manipulation of [Ca2+]i, indicates that they may play a role in establishing and maintaining these essential boundaries. Signals visualized from the PSM were also stochastic with respect to location and time, and again took the form of localized intercellular Ca2+ waves generated by Ca2+ release via IP3Rs. They were predominantly generated in a region of the PSM that displayed some correlation with the expression pattern of the zebrafish homologue (her1) of the Drosophila pair-rule gene Hairy, which is involved in generating periodicity during somitogenesis and has been suggested to be linked to Ca2+ signaling. Experimentation indicated, however, that there appeared to be no linkage between the PSM Ca2+ transients visualized and her1 expression patterns. Signals generated by the notochord were also chaotic and generated by Ca2+ release via IP3Rs. Their biological function remains unclear. It is thus suggested that the transients generated by these three embryological domains represent a new class of stochastic dev

Ran is a small GTP-binding protein involved in several essential roles for cell viability. This observation implies Ran might be ubiquitously expressed during development. However, Ran shows a differentiated expression pattern that is restricted to specific tissues from embryo to adult. At early embryonic stages of mouse development we found persistent Ran expression in proliferating neural tissue, neural crest derived dorsal root ganglions and sensory pits. We also showed an accumulation of Ran transcripts in main embryonic haematopoietic tissues: blood islands first and then hepatic bud. In advanced stages of development Ran is also expressed in other tissues showing a high cell turnover.

We have isolated a novel chick Eph-related receptor that corresponds to the EphA7 gene. Within the nervous system, EphA7 expression is restricted to prosomeres 1 and 2 in the diencephalon and all the rhombomeres in the hindbrain during segmentation stages. Later on, a superimposed pattern appears that correlates with the formation of several axonal tracts. In the somitic mesoderm, the expression correlates with segmentation and the guidance of both neural crest and motor axons through the sclerotomes.