Dynamic somite cell rearrangements lead to distinct waves of myotome growth

The myogenic precursors responsible for muscle growth in amniotes develop from thedermomyotome, an epithelium at the external surface of the somite. In teleosts, themyogenic precursors responsible for growth have not been identified. We have usedsingle cell lineage labeling in zebrafish to show that anterior border cells of epithelialsomites are myogenic precursors responsible for zebrafish myotome growth. These cellsmove to the external surface of the embryonic myotome and express the transcriptionfactor Pax7. Some remain on the external surface and some incorporate into the fastmyotome, apparently by moving between differentiated slow fibres. The posterior cellsof the somite, in contrast, elongate into medial muscle fibres. The surprising movementof the anterior somite cells to the external somite surface transforms a segmentallyrepeated arrangement of myogenic precursors into a medio-lateral arrangement similar tothat seen in amniotes.Fil: Stellabotte, Frank. Ohio Wesleyan University.; Estados UnidosFil: Dobbs McAuliffe, Betsy. Ohio Wesleyan University.; Estados UnidosFil: Fernandez, Daniel Alfredo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentina. Universidad Nacional de Tierra del Fuego; ArgentinaFil: Feng, Xuesong. Ohio Wesleyan University.; Estados UnidosFil: Devoto, Stephen Henry. Ohio Wesleyan University.; Estados Unido

Embryological manipulations in the developing Xenopus inner ear reveal an intrinsic role for Wnt signaling in dorsal–ventral patterning

Background: The inner ear develops from an ectodermal thickening known as the otic placode into a complex structure that is asymmetrical along both the anterior–posterior (A-P) and dorsal–ventral (D-V) axes. Embryological manipulations in Xenopus allow us to test regenerative potential along specific axes and timing of axis determination. We explore the role of Wnt signaling with gain and loss of function experiments. Results: In contrast to A or P half ablations, D or V half ablations almost never result in mirror duplications or normal ears. Instead there is a loss of structures, especially those associated with the ablated region. Rotation experiments inverting the D-V axis reveal that it is determined by stage 24–26 which is just before expression of the dorsal otic marker Wnt3a. Conditional blocking of canonical Wnt signaling results in reductions in the number of sensory organs and semicircular canals which could be placed in one of three categories, the most common phenotypes being similar to those seen after dorsal ablations. Conclusions: There is less regenerative potential along the D-V axis. Wnt3a protein alone is sufficient to rescue the severe loss of inner ear structures resulting from dorsal but not ventral half ablations