Development and innervation of the abdominal muscle in embryonic Xenopus laevis

Abstract

The morphogenesis and innervation of the ventral abdominal musculature in Xenopus embryos was examined using microscopic techniques. Muscle development begins at Nieuwkoop and Faber Stage 31, when aggregates of undifferentiated cells form on the ventrolateral margins of rostral trunk myotomes. During subsequent stages, aggregates form and detach from progressively more caudal myotomes to form a series of seven discrete cell clusters (anlagen). The anlagen migrate ventrally in a cell-free space between the epidermis and a subepidermal layer of pigment cells. Extracellular aggregates of 30-nm granules are evident transiently between the migrating anlagen and the epidermis. During stages 39 and 40, each anlage transforms into a sheet of myotubes which attaches rostrally and caudally to adjacent sheets to form a seven-segmented muscle. The series of broad segments, approximately one fiber thick, extends from the pericardium to the level of the proctodeum. The embryonic muscle is innervated by the ventral rami of spinal nerves 2 to 9. The major nerve trunks to the muscle develop between stages 35/36 and 40. Axons initially grow ventrally along the paths taken by the muscle anlagen. When the anlagen become muscle segments, the nerves are deep to the narrow boundaries between the segments. Spinal nerve 2 ramifies in the first muscle segment and sends fibers rostrally to the geniohyoid muscle. The findings represent the first description of the development of this muscle in Xenopus and the first account of the development of the abdominal motor nerves in an amphibian embryo.

Spatio‐temporal pattern formation of abdominal muscle inxenopus laevis

“…The present lineage tracing study with a-cardiac actin cDNA probe and anti-sarcomeric actin monoclonal antibody confirmed the previous report (Lynch, 1990) that cells of abdominal muscle originated from the myotomes of dorsal mesoderm and clearly showed the migration pattern of abdominal muscle anlagen (Figs. 2 and 3).…”

“…However, the mechanism of abdominal muscle migration to form ventral trunk musculature has been unrevealed until electron microscopic observations showing the general migration pattern of abdominal muscle in Xenopus laevis (Lynch, 1990). Genetic and molecular approaches to understand muscle development revealed a number of myoD family genes, the regulation mechanisms of gene expression, and morphological changes of muscle cells during differentiation.…”

A novel role forlbx1inXenopushypaxial myogenesis

“…However, these tadpoles do contain hypaxial muscles, which form the rectus abdominus muscles (Lynch, 1990;Martin and Harland, 2001;Ryke, 1953). These are homologous to the inter-limb body wall muscles of amniotes (McDiarmid and Altig, 1999).…”

Expression of the Xenopus homologue of the receptor for activated C-kinase 1 (RACK1) in the Xenopus embryo

“…3J.) This cell mass was abdominal muscle anlagen (precursor tissue of abdominal muscle), which migrates ventrally, expands, and differentiates into muscle (Lynch 1990). XRACK1 expression was also present in presumptive premigratory abdominal muscle cells and this continued during subsequent stages.…”