Expression of β1 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 β1 class integrins both at mRNA and protein levels. Using the reverse transcriptional polymerase chain reaction and oligonucleotide primers based on the DNA sequence of mouse integrins, the RNA transcripts for the β1, α5 and α6 subunits were detected in unfertilized oocytes. The expression of the mRNAs is paralleled by the expression of the corresponding proteins, in fact, the α5/β1 and the α6/β1 complexes can be immunoprecipitated with specific antibodies from ¹²⁵I-surface-labeled oocytes. Using subunit-specific antibodies we also demonstrate the presence of the α3/β1 at the oocyte surface but α1, α2, α4 or αV subunits were not detectable. Since the mouse α3 DNA sequence is not available, we have not tested for the corresponding transcript. Integrin subunits α6 and β1 were differently distributed on the oocyte surface, as visualized by immunofluorescence staining and by immunoelectron microscopy. α6 antigen was mainly confined to the microvillous area of the oocyte surface, while β1 was more homogenously distributed over the whole oolemma. These data demonstrate for the first time the expression of three β1 integrin complexes in unfertilized mouse oocytes. Such proteins may have a role in sperm-egg interaction or during very early steps of embryogenesis.