Defects in adhesion and migration, but not in proliferation and differentiation, of embryonic stem cells upon replacement of integrin subunit beta 1Aby beta 1D

beta 1D is a skeletal muscle-specific splice variant of the betai integrin subunit, while beta IA integrin subunit has a wide tissue distribution. We have previously shown that replacement of beta 1A by beta 1D by homologous recombination (knockin) in all mouse tissues was embryonic lethal. Through two successive rounds of homologous recombination, we have now produced emb ryonic stem (ES) cells expressing beta 1D instead of beta 1A, and analyzed the ability of beta ID to support ES cell differentiation in vitro and in t eratomas in vivo, beta 1D knockin (KI) ES cells grew at a similar rate but as more compact colonies than the beta 1A-expressing cells. Increased cell cohesiveness, however, did not appear to involve changes in cadherin activi ty. Although in both beta 1A and beta ID-KI ES cells only one pi allele is active; the expression of pi integrins in the beta 1D-KI ES cells was reduc ed by 50%, compared with that in the beta 1A-expressing cells; this correla ted with impaired adhesive and migratory capacities. It appeared that durin g in vitro cardiac differentiation, in spite of a slight delay in the induc tion of two cardiac-specific transcripts, the alpha- and beta -myosin heavy chains, contracting cardiomyocytes were detected in similar numbers and at the same time in embryoid bodies (EB) derived from beta 1D-KI and from bet a 1A cells. Furthermore, replacement of beta 1A by beta 1D in ES cells did not affect neurite differentiation in embryoid bodies in the presence of re tinoic acid suggesting that beta 1D supports neurogenesis. However, the imp aired migration of other cells from the EB, including endodermal cells, pre vented the normal outgrowth of neurites in beta 1D-KI EB. Finally, injectio n of BID-KI ES cells in the flank of syngeneic mice gave rise to fully deve loped teratomas containing simple and pluristratified epithelia, muscle, ca rtilage, blood vessels, and tissues from the neural lineage. These results show that the muscle-specific splice variant beta 1D, in spite of its speci fic cytoplasmic domain, supports the differentiation of many cell types. Th is further suggests that the embryonic lethality in the beta 1D-KI embryos was mainly due to the different ability of beta IA and beta 1D to mediate c ell adhesion and migration.