Integrins, by signaling between extracellular matrix and cell nucleus, serve critical roles in cell proliferation and survival. A knock-in mice was developed by a targeted deletion of the C-terminal segment of the cytoplasmic tail of beta 4-integrin (beta 4-1355T). The beta 4-1355T mice had a longer gestational length, smaller litter sizes, lower fecundity rate, and higher frequency of early pregnancy loss. beta 4-1355T embryos demonstrated a high degree of fragmentation and asymmetry, with fewer surviving to either a morula or blastocyst stage. In wild-type oocytes and embryos, beta1, beta 4, and laminin-5 signals colocalized at the opposing surfaces of blastomeres and between the polar bodies and oocytes. Blastomeres within the beta 4-1355T embryos were less cohesive, with a more diffuse expression of beta 4 and laminin-5 compared with wild type. The alpha 6 beta 4_laminin-5 interaction appears to be vital for maintaining the cohesiveness between the cells of the embryo. Deciphering the role of integrins such as beta 4 in embryogenesis may help explain in vitro fertilization failures.