Interaction between epithelial basement membrane and migrating mesoblast cells in the avian blastoderm

Abstract

We investigated the remodelling of glucosamine-containing basement-membrane components in chimaeric avian embryos during gastrulation. Epiblast grafts metabolically labelled with tritiated glucosamine were excised from gastrulating quail embryos and implanted orthotopically into chicken embryos at the same developmental stage. The chimaerae were allowed to develop in culture for 5–7 h before autoradiographic processing. The resulting autoradiographs not only showed the presence of silver grains in the grafted quail tissue and at the level of its basement membrane, but also revealed labelling in the basement-membrane region of the chicken tissue lateral to the graft, i.e. between the mesoblast and epiblast. This last labelling extended as far as at the edge of the area pellucida, i.e. in a region of chicken tissue situated more laterally than the initial position of the graft. No labelling was observed medial, anterior, or posterior to the graft. This observation argues against the interpretation that our results were due to diffusion of labelled compounds within the basement membrane. We also provide evidence to exclude the possibility that quail epiblast cells migrated on their own underlying basement membrane, leaving behind a carpet of labelled material. Taking into account, firstly, the morphogenetic movements that occur during gastrulation, i.e. the movement of epiblast cells towards the primitive streak where they ingress, and the migration of mesoblast cells along the basement membrane towards the periphery of the area pellucida, and secondly, the medial movement of the basement membrane, it is suggested that mesoblast cells picked up labelled compounds in the basement membrane of the graft and left these behind during their lateral migration. Thus, the remodelling of epithelial basement-membrane components may be mediated by migrating mesen-chymal cells.