Two myogenic lineages within the developing somite

TLDR

Muscle tissues arise from somites, with axial muscles originating from somite proper cells and limb muscles from cells that migrate away, and recent evidence indicates these two muscle types may derive from distinct developmental lineages. The study aimed to test whether medial and lateral halves of somites give rise to distinct muscle lineages. Using microsurgical separation of medial and lateral somite halves and a chick‑quail nucleolar marker system, the researchers traced the developmental fate of each half. The medial half of a newly formed somite exclusively produced myotome and sclerotome, whereas the lateral half largely migrated to form limb muscle and other mesenchymal tissues, and graft experiments confirmed that fate is position‑dependent, supporting the existence of at least two distinct myogenic lineages.

Abstract

It is well known that the muscles of the vertebrate body are derived from the somite. Precursor cells within the somite proper form the back or axial muscles while other precursor cells migrate away from the somite to populate the muscle of the limbs and ventral body wall. Although both types of muscle are generally thought of as arising from a common progenitor population, the myotome, recent evidence points to developmental differences in these two groups of muscles which may reflect different developmental lineages. To test the lineage hypothesis, we used microsurgery and the chick-quail nucleolar marker system to follow the developmental fate of the lateral and medial halves of somites at the wing level. The results showed that the structures of the mature somite (myotome and sclerotome) are derived virtually exclusively from cells residing in the medial half of the newly formed somite. On the other hand, virtually all of the cells residing in the lateral half of the newly formed somite are destined to leave the somite proper and populate the limb muscle and, probably, other somite-derived mesenchymal structures in the limb and ventral body wall. Switch-graft experiments show that the two halves of newly formed somites are largely interchangeable demonstrating that their ultimate developmental fate is position-dependent and that it becomes fixed as a result of extrinsic influences which act during later stages of somitogenesis. We conclude that at least two distinct myogenic lineages exist in the somite; one giving rise to the muscles of the back and the other giving rise to the limb musculature.