Migration of hypoglossal myoblast precursors

The intrinsic hypoglossal musculature develops from precursor myoblasts whi ch undergo long-range migration from the occipital somites to the tongue. L ittle detail is known about the precise spatiotemporal pathway taken by the se cells or the factors controlling migration. In this study, chick/quail c himeras in which the occipital paraxial mesoderm is quail derived, reveal t hat the pathway taken by the tongue muscle progenitors is both complex and highly specific. Precursor myoblasts are Pax-3 positive cells which descend from the somite and migrate around the pharyngeal endoderm, They then cour se rostrally, following the base of the pharynx, remaining in a tight stran d. We have examined a number of factors implicated in the control of migrat ion of the hypoglossal precursors. Replacement of the occipital somites wit h those originating in the flank reveals that intrinsic differences do not exist between these somites with respect to their capacity to respond to mi gratory cues. The lack of high level HGF/SF expression along the pathway of the migrating hypoglossal precursors suggests that this factor is not invo lved in the actual process of migration of the hypoglossal precursors to th e tongue. The pathway followed by the migrating precursors is identical to that of both the developing hypoglossal nerve and the circumpharyngeal cres t-a subpopulation of the cranial neural crest, and importantly these popula tions utilize this pathway before the myoblast precursors. However, ablatio n neither of the hypoglossal nerve nor of the neural crest results in a per turbation in the ability of this Pax-3 positive population to migrate. This demonstrates that migration of the precursors is independent of both of th ese cell populations, and that it is controlled by the peripheral tissues. Dev. Dyn. 1998;213:349-358. (C) 1998 Wiley-Liss, Inc.