Disruption of the talin gene arrests mouse development at the gastrulationstage

Studies on cultured cells show that the cytoskeletal protein talin plays a key role in cell spreading and the assembly of cell-extracellular matrix ju nctions. To examine the role of talin in vivo, we have generated mice with a targeted disruption of the talin gene. Heterozygotes are normal, but no s urviving homozygous mutant animals were obtained, proving that talin is req uired for embryogenesis. Mutant embryos develop normally to the blastocyst stage and implant, but there is a gross disorganization of the embryos at g astrulation (6.5-7.5 days post coitum), and they die around 8.5-9.5 days po st coitum. The embryonic ectoderm is reduced in size, with fewer cells, and is incompletely organised compared with wildtype embryos. The mutant embry os show disorganised extraembryonic tissues, and the ectoplacental and exco coelomic cavities are not formed. This seems to be because embryonic mesode rm accumulates as a mass on the posterior side of the embryos and fails to migrate to extraembryonic regions, although mesodermal cells are evident in the embryo proper. Spreading of trophoblast cells derived from cultured mu tant blastocysts on fibronectin and laminin is also considerably reduced. T herefore, the fundamental deficit in these embryos seems to be a failure of cell migration at gastrulation. (C) 2000 Wiley-Liss, Inc.