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¹ Prince Henry’s Institute of Medical Research, Monash Medical Centre, Clayton, Victoria 3168, Australia
² Department of Anatomy and Cell Biology, Monash University, PO Box 5152, Level 4, Block E, 246 Clayton Road, Clayton, Victoria 3168, Australia

(Requests for offprints should be addressed to L O’Donnell; Email: liza.odonnell{at}princehenrys.org)

Spermiation is the final step of spermatogenesis and culminates in the disengagement (release) of elongated spermatids from Sertoli cells into the seminiferous tubule lumen. Spermiation failure, wherein spermatids are retained by Sertoli cells instead of releasing, occurs after hormone suppression. The mechanisms involved in spermatid disengagement and retention are not well understood. We previously showed that ß₁-integrin is associated with spermatids until the point of disengagement, but the ectoplasmic specialisation junction (ES) is not. The aims of this paper are to further characterise the complex that is present immediately prior to spermatid disengagement by identifying the -integrin form dimerised with ß₁-integrin, localising focal adhesion kinase (FAK) and determining if microtubules are involved. Adult Sprague–Dawley rats received testosterone and oestradiol implants and an FSH antibody for 7 days to suppress testicular testosterone and FSH and induce spermiation failure. Control rats were treated with saline. Immunohistochemical analysis showed that ₆-integrin and a phosphorylated form of FAK (FAK-Tyr³⁹⁷) are present between late spermatids and Sertoli cells after ES removal, until the point of disengagement, and both proteins remain associated with retained spermatids after spermiation failure induced by hormone suppression. Using dual-label immunofluorescence, tubulins (and thus microtubules) were observed to co-localise with ES, but were neither associated with elongated spermatids just prior to release nor with retained spermatids following hormone suppression. These results suggest that microtubules are not involved in the final release of spermatids from Sertoli cells. We conclude that spermatid release during spermiation is mediated by a ‘disengagement complex’ containing ₆ß₁-integrin and phospho-FAK, the function of which can be affected by gonadotrophin suppression.