Expression of beta 1 integrin complexes on the surface of unfertilized mouse oocyte

Integrins are a family of cell surface receptors that mediate cell-cell and cell-matrix interactions in a variety of different cellular systems. Here we show that unfertilized mouse oocytes express beta 1 class integrins both at mRNA and protein levels. Using the reverse transcription polymerase chain reaction and oligonucleotide primers based on the DNA sequence of mouse integrins, the RNA transcripts for the beta 1, alpha 5 and alpha 6 subunits were detected in unfertilized oocytes. The expression of the mRNAs is paralleled by the expression of the corresponding proteins, in fact, the alpha 5/beta 1 and the alpha 6/beta 1 complexes can be immunoprecipitated with specific antibodies form 125I-surface-labeled oocytes. Using subunit-specific antibodies we also demonstrate the presence of the alpha 3/beta 1 at the oocyte surface but alpha 1, alpha 2, alpha 4 or alpha V subunits were not detectable. Since the mouse alpha 3 DNA sequence is not available, we have not tested for the corresponding transcript. Integrin subunits alpha 6 and beta 1 were differently distributed on the oocyte surface, as visualized by immunofluorescence staining and by immunoelectron microscopy. alpha 6 antigen was mainly confined to the microvillous area of the oocyte surface, while beta 1 was more homogeneously distributed over the whole oolemma. These data demonstrate for the first time the expression of three beta 1 integrin complexes in unfertilized mouse oocytes. Such proteins may have a role in sperm-egg interaction or during very early steps of embryogenesis.