The pattern of MyoD and contractile protein localization in primary epaxial myotome reflects the dynamic progression of nascent myoblast differentiation

Abstract

The localization of contractile and regulatory proteins in early stages of epaxial primary myotome development was analyzed by immunofluorescence microscopy. Contractile proteins that appear in an ordered sequence in the rostro-caudal axis of somite development were found to reiterate that sequence in the dorso-medial-to-ventro-lateral axis of primary epaxial myotome development. Pair-wise localization of MyoD-titin, desmin-titin, and desmin-myosin defined three zones extending from the dermomyotome dorso-medial lip (DML) into the primary myotome layer. Zones M1 and M2, which were positive for MyoD ؉ titin and MyoD ؉ titin ؉ desmin, respectively, were restricted to the dorso-medial-most extremity of the myotome layer and did not expand during the course of myotome development. Zone M3 was positive for MyoD, desmin, titin, myosin, and cardiac troponin T and was the only zone that expanded during primary myotome development. Myotome fibers in zone M3 were unit-length, spanning the full rostro-caudal axis of the myotome while fibers in zones M1 and M2 were shorter than unit length. Anti-myoD immunofluorescence, when detected in cells lacking contractile-protein-positive cytoplasm, was restricted to the DML and nascent myotome cells immediately subjacent to the DML. These results demonstrate a dynamic spatiotemporal sequence in the differentiation program of nascent myotome cells as they emerge from the DML; zones M1 and M2 reflect standing waves of sequential contractile protein activation during the maturation of nascent myotomal myoblasts, while the expanding zone M3 reflects the accumulation of mature myotome fibers expressing a full cohort contractile proteins. Developmental Dynamics 235:382-394, 2006.

Somite cell cycle analysis using somite‐staging to measure intrinsic developmental time

“…1E, arrow b) has the potential to measure stage‐dependent changes that are common to all somites. Formation of the segmental myotome is a highly‐ordered, stage‐dependent process (Yang and Ordahl,2006; and references therein), which occurs in all somites, including occipital somites (Huang et al,1997). Desmin‐positive cells are first detectable in the primary epaxial myotome of forelimb somites at ssVII (Kaehn et al,1988), and the rate of increase in new desmin‐positive cells is constant during forelimb level somite development (Borman et al,1994; Borman and Yorde,1994a).…”

“…3A). The well‐ordered translocation of new myotome cells asymmetrically, at the dorsomedial margin of the myotome layer, results in the expansion of the epaxial myotome in each segment during the next 3+ days of embryonic development (Denetclaw et al,1997,2001; Denetclaw and Ordahl,2000; Venters and Ordahl,2002; Yang and Ordahl,2006). At the forelimb level, hypaxial muscle precursor cells migrate from the ventrolateral lip of the dermomyotome (VLL) to populate the adjacent limb bud (reviewed in Christ and Ordahl,1995).…”

Development of the epaxial muscles in the human embryo

“…The dorsolateral parts of the somites differentiate into dermomyotomes and the ventromedial parts into sclerotomes (Furst et al, ; Venters et al, ; Sacks et al, ; Scaal and Christ, ). During primary myotome formation, a layer of longitudinally oriented, myosin‐expressing cells forms underneath the dermomyotome (Venters et al, ; Yang and Ordahl, ). Subsequently, the myotome becomes polarized and forms dorsomedial (DML) (Ordahl et al, ) and ventrolateral lips (VLL) (Denetclaw et al, ), which give rise to the epaxial and hypaxial muscles, respectively.…”

A NLRR-1 gene is expressed in migrating slow muscle cells of the trout (Oncorhynchus mykiss) embryo

“…In this regard, one can note that, in contrast to what has been reported in the mouse, the expression of NLRR-1 in fish somites does not resemble that of the Myf5 but correlates with the adaxial expression of MyoD. Nevertheless, in spite of these divergences between adaxial cells in fish and myogenic cells of the dorsal lip in amniotes, some similarities subsist: They are both the first to differentiate in the embryonic myotome (Yang and Ordahl 2006;Devoto et al 1996;Chauvigne et al 2005;Bryson-Richardson et al 2005), and their differentiation depends on the activity of notochord-derived hedgehog proteins (Currie and Ingham 1998). In this regard, it would be of interest to determine whether the expression of NLRR-1 in myotome cells is also regulated by hedgehog proteins.…”