Complex architecture and regulated expression of the Sox2ot locus during vertebrate development

The Sox2 gene is a key regulator of pluripotency embedded within an intron of a long noncoding RNA (ncRNA), termed Sox2 overlapping transcript (Sox2ot), which is transcribed in the same orientation. However, this ncRNA remains uncharacterized. Here we show that Sox2ot has multiple transcription start sites associated with genomic features that indicate regulated expression, including highly conserved elements (HCEs) and chromatin marks characteristic of gene promoters. To identify biological processes in which Sox2ot may be involved, we analyzed its expression in several developmental systems, compared to expression of Sox2. We show that Sox2ot is a stable transcript expressed in mouse embryonic stem cells, which, like Sox2, is down-regulated upon induction of embryoid body (EB) differentiation. However, in contrast to Sox2, Sox2ot is up-regulated during EB mesoderm-lineage differentiation. In adult mouse, Sox2ot isoforms were detected in tissues where Sox2 is expressed, as well as in different tissues, supporting independent regulation of expression of the ncRNA. Sox2dot, an isoform of Sox2ot transcribed from a distal HCE located >500 kb upstream of Sox2, was detected exclusively in the mouse brain, with enrichment in regions of adult neurogenesis. In addition, Sox2ot isoforms are transcribed from HCEs upstream of Sox2 in other vertebrates, including in several regions of the human brain. We also show that Sox2ot is dynamically regulated during chicken and zebrafish embryogenesis, consistently associated with central nervous system structures. These observations provide insight into the structure and regulation of the Sox2ot gene, and suggest conserved roles for Sox2ot orthologs during vertebrate development

Cadherin-Mediated Differential Cell Adhesion Controls Slow Muscle Cell Migration in the Developing Zebrafish Myotome

AbstractSlow-twitch muscle fibers of the zebrafish myotome undergo a unique set of morphogenetic cell movements. During embryogenesis, slow-twitch muscle derives from the adaxial cells, a layer of paraxial mesoderm that differentiates medially within the myotome, immediately adjacent to the notochord. Subsequently, slow-twitch muscle cells migrate through the entire myotome, coming to lie at its most lateral surface. Here we examine the cellular and molecular basis for slow-twitch muscle cell migration. We show that slow-twitch muscle cell morphogenesis is marked by behaviors typical of cells influenced by differential cell adhesion. Dynamic and reciprocal waves of N-cadherin and M-cadherin expression within the myotome, which correlate precisely with cell migration, generate differential adhesive environments that drive slow-twitch muscle cell migration through the myotome. Removing or altering the expression of either protein within the myotome perturbs migration. These results provide a definitive example of homophilic cell adhesion shaping cellular behavior during vertebrate development

Development and Evolution of the Muscles of the Pelvic Fin

Locomotor strategies in terrestrial tetrapods have evolved from the utilisation of sinusoidal contractions of axial musculature, evident in ancestral fish species, to the reliance on powerful and complex limb muscles to provide propulsive force. Within tetrapods, a hindlimb-dominant locomotor strategy predominates, and its evolution is considered critical for the evident success of the tetrapod transition onto land. Here, we determine the developmental mechanisms of pelvic fin muscle formation in living fish species at critical points within the vertebrate phylogeny and reveal a stepwise modification from a primitive to a more derived mode of pelvic fin muscle formation. A distinct process generates pelvic fin muscle in bony fishes that incorporates both primitive and derived characteristics of vertebrate appendicular muscle formation. We propose that the adoption of the fully derived mode of hindlimb muscle formation from this bimodal character state is an evolutionary innovation that was critical to the success of the tetrapod transition

Des mutations permettant au virus de Newcastle d'échapper à la neutralisation virale sont localisées à la fois sur les fragments F1 et F2 de la protéine de fusion

Doctorat en Sciencesinfo:eu-repo/semantics/nonPublishe

Calcium-Dependent Adhesion Is Necessary for the Maintenance of Prosomeres

Cell adhesion has been suggested to function in the establishment and maintenance of the segmental organization of the central nervous system. Here we tested the role of different classes of adhesion molecules in prosencephalic segmentation. Specifically, we examined the ability of progenitors from different prosomeres to reintegrate and differentiate within various brain regions after selective maintenance or removal of different classes of calcium-dependent versus -independent surface molecules. This analysis implicates calcium-dependent adhesion molecules as central to the maintenance of prosomeres. Only conditions that spared calcium-dependent adhesion systems but ablated more general (calcium-independent) adhesion systems resulted in prosomere-specific integration after transplantation. Among the members of this class of adhesion molecules, R-cadherin shows a striking pattern of prosomeric expression during development. To test whether expression of this molecule was sufficient to direct progenitor integration to prosomeres expressing R-cadherin, we used a retroviral-mediated gain-of-function approach. We found that progenitors originally isolated from prosomere P2 (a region which does not express R-cadherin), when forced to express this molecule, can now integrate more readily into R-cadherin-expressing regions, such as the cortex, the ventral thalamus, and the hypothalamus. Nonetheless, our analysis suggests that while calcium-dependent molecules are able to direct prosomere-specific integration, they are not sufficient to induce progenitors to change their regional identity. While diencephalic progenitors from R-cadherin-expressing regions of prosomere 5 could integrate into R-cadherin-expressing regions of the cortex, they did not express the cortex-specific gene Emx1 or the telencephalic-specific gene Bf-1. Furthermore, diencephalic progenitors that integrate heterotopically into the cortex do not persist postnatally, whereas the same progenitors survive and differentiate when they integrate homotopically into the diencephalon. Together our results implicate calcium-dependent adhesion molecules as key mediators of prosomeric organization but suggest that they are not sufficient to bestow regional identities

Telencephalic progenitors maintain anteroposterior identities cell autonomously

Grafting experiments have demonstrated that determination of anteroposterior (AP) identity is an early step in neural patterning that precedes dorsoventral (DV) specification [1,2]. These studies used pieces of tissue, however, rather than individual cells to address this question. It thus remains unclear whether the maintenance of AP identity is a cell-autonomous property or a result of signaling between cells within the grafted tissue. Previously, we and others [3–5] have used transplants of dissociated brain cells to show that individual telencephalic precursor cells can adopt host-specific DV identities when they integrate within novel regions of the telencephalon. We have now undertaken a set of transplantations during the same mid-neurogenic period used in the previous studies to assess the ability of telencephalic progenitors to integrate and differentiate into more posterior regions of the neuraxis. We observed that telencephalic progenitors were capable of integrating and migrating within different AP levels of the central nervous system (CNS). Despite this, we found that telencephalic progenitors that integrated within the diencephalon and the mesencephalon continued to express a telencephalic marker until adulthood. We speculate that during neurogenesis individual progenitors are determined in terms of their AP but not their DV identity. Hence, AP identity is maintained cell autonomously within individual progenitors