Rat seminiferous epithelium contains a unique junction (ectoplasmic specialization) with signaling properties both of cell/cell and cell/matrix junctions

The seminiferous epithelium contains unique actin related cell-cell junctio ns, termed ectoplasmic specializations (ESs). Turnover of these junctions i s fundamental to sperm release and to movement of spermatocytes from basal to adluminal compartments of the epithelium during spermatogenesis. In this study we report several novel observations related to the spatial and temp oral distribution of integrin-related signaling molecules at ESs. We confir m the presence of beta (1)-integrin at these sites and further demonstrate co-localization of integrin linked kinase (ILK). beta (1)-Integrin and ILK were shown by immunoprecipitation to associate in whole cell lysates of sem iniferous epithelium. This observation provides the first evidence for a di rect beta (1)-integrin/ILK interaction in noncultured epithelium. Pan-cadhe rin and beta -catenin antibodies did not react at ESs. Rather, antibodies r eacted with desmosome-like junctions that are present both at basal junctio nal complexes between Sertoli cells and at sites of attachment to spermatog enic cells. Focal adhesion kinase (FAK), a known integrin-associated molecu le, did not codistribute with beta (1)-integrins and did not associate with these adhesion molecules in immunoprecipitation studies. Although FAK was expressed in the epithelium, it appeared to be limited to the cytoplasm of early spermatogenic cells. Significantly, polyclonal antibodies against pho sphotyrosine-containing residues reacted strongly at ESs, with highest leve ls detected during sperm release and turnover of basal junction complexes. Our observations indicate that ESs share cell signaling features both of ce ll-cell junctions and of cell-extracellular matrix junctions.