Lack of β1 integrin gene in embryonic stem cells affects morphology, adhesion, and migration but not integration into the inner cell mass of blastocysts

Abstract

A gene trap-type targeting vector was designed to inactivate the β1 integrin gene in embryonic stem (ES) cells. Using this vector more than 50% of the ES cell clones acquired a disruption in the β1 integrin gene and a single clone was mutated in both alleles. The homozygous mutant did not produce β1 integrin mRNA or protein, while α3, α5, and α6 integrin subunits were transcribed but not detectable on the cell surface. Heterozygous mutants showed reduced β1 expression and surface localization of α/β1 heterodimers. The αV subunit expression was not impaired on any of the mutants. Homozygous ES cell mutants lacked adhesiveness for laminin and fibronectin but not for vitronectin and showed a reduced association with a fibroblast feeder layer. Furthermore, they did not migrate towards chemoattractants in fibroblast medium. None of these functions were impaired in heterozygous mutants. Scanning electron microscopy revealed that homozygous cells showed fewer cell-cell junctions and had many microvilli not usually found on wild type and heterozygous cells. This profound change in cell shape is not associated with gross alterations in the expression and distribution of cytoskeletal components. Unexpectedly, microinjection into blastocysts demonstrated full integration of homozygous and heterozygous mutants into the inner cell mass. This will allow studies of the consequences of β1 integrin deficiency in several in vivo situations.