The Primitive Endoderm Segregates from the Epiblast in β1 Integrin-Deficient Early Mouse Embryos

Abstract

We analyzed the mechanism of developmental failure in implanted β1 integrin-null blastocysts and found that primitive endoderm cells are present but segregate away from, instead of forming an epithelial layer covering, the inner cell mass. This cell segregation phenotype was also reproduced in β1 integrin-null embryoid bodies, in which primitive endoderm cells segregated and appeared as miniature aggregates detached from the core spheroids, and a primitive endoderm layer failed to form on the surface. Restricted β1 integrin gene deletion in embryos using Ttr-Cre or Sox2-Cre indicated that the loss of integrin function in the cells of the inner core rather than the outer layer is responsible for the failure to form a primitive endoderm layer. We conclude that β1 integrin is essential for the attachment of the primitive endoderm layer to the epiblast during the formation of a basement membrane, a process concurrent with the transition from cadherin- to integrin-mediated cell adhesion.

ACKNOWLEDGMENTS

We appreciate the gift of the β1 integrin-null and -heterozygous control ES cells from Reinhard Fässler via Lionel Larue (Institut Curie, France). We also appreciate the Ttr-Cre mice from Anna-Katerina Hadjantonakis (Memorial Sloan-Kettering Institute, New York, NY).We appreciate valuable comments from our colleagues, including Yue Meng, Santas Rosario, and James Hoy, for reading, suggestions, and comments on the manuscript. We are indebted to George T. McNamara (University of Miami Analytical Imaging Core Facility) for assistance with confocal microscopy and Margaret Bates (University of Miami Electron Microscope Core Facility) with transmission electron microscopy.

The work is supported by R01 CA095071, CA79716, and CA75389 to X.-X. Xu from NCI, NIH. R.M. is supported by the Sylvester Comprehensive Cancer Center and an American Cancer Society Institutional Research Grant (IRG-98-277-09).