Appearance and distribution of laminin during development of Xenopus laevis.

A cloned cDNA fragment, homologous to domain II of the mouse laminin B1 chain, was obtained from a Xenopus neurula cDNA library. Using this probe Northern-blot analysis over the course of embryogenesis revealed a first signal of a laminin transcript at midgastrula (stage 11). Affinity-purified polyclonal antibodies directed against Xenopus laminin were obtained via a lacZ fusion protein. Immunohistology demonstrated the appearance of the antigen at about one developmental stage after the detection of the transcript. At stage 12 1/2 a faint immunofluorescence staining surrounded the developing notochord and somitogenic mesodermal cells. Thereafter laminin appeared in distinct locations outlining notochord, somites and neural tube. The epidermal basement membrane seemed to be endowed with laminin only at the relatively late postneurula stage. The observation that laminin could not be detected before stage 12 1/2 is discussed with respect to a proposed role of laminin in the gastrulation process.