At the end of spermatogenesis, elongated spermatids are released from supporting Sertoli cells via the process termed spermiation. Previous studies have shown that spermiation failure occurs after hormone suppression, in which spermatids are retained instead of releasing. However, the molecular mechanisms involved in spermiation and spermiation failure are largely unknown. The aims of the present study were, first, to characterize the ultrastructural events associated with normal spermiation and spermiation failure using light and electron microscopy and, second, to investigate the localization of cell adhesion-associated (beta1-integrin and cadherins) and junction-associated molecules (integrin-associated kinase [ILK], beta-catenin, and espin) during these processes. Four adult Sprague-Dawley rats received testosterone and estradiol implants and FSH antibody (2 mg kg-1 day-1) for 7 days to suppress testicular testosterone and FSH and to induce spermiation failure. Four rats treated with saline were used as controls. After testosterone and FSH suppression, spermiation at the ultrastructural level appeared to be normal until the final disengagement of the spermatids from Sertoli cells (stage VIII), at which stage a large number of retained spermatids were noted. Immunohistochemical localization of espin showed that during spermiation, removal of the ectoplasmic specialization (ES) occurred 30 h before spermatid disengagement, suggesting that non-ES junctions mediate the spermatid-Sertoli cell interaction before and during disengagement. beta1-Integrin and beta-catenin remained associated with spermatids after ES removal and until disengagement; however, ILK was removed along with the ES. Though detectable, N-cadherin was not associated with the spermatid-Sertoli cell junction. After testosterone and FSH suppression, beta1-integrin, but not N-cadherin or beta-catenin, remained associated with spermatids that failed to spermiate. In conclusion, hormone suppression-induced spermiation failure is caused by defects in the disengagement of spermatids from the Sertoli cell, and this process likely is mediated by beta1-integrin in an ILK-independent mechanism.

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 b 1 -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 a-integrin form dimerised with b 1 -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 a 6 -integrin and a phosphorylated form of FAK ) 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 a 6 b 1 -integrin and phospho-FAK, the function of which can be affected by gonadotrophin suppression.

This study investigates the suitability of surface-enhanced laser desorption and ionization time-of-flight (SELDI-TOF) and electrospray ionization (ESI) mass spectrometry for analysis of the proteins released by the mouse preimplantation embryo in vitro. SELDI-TOF analysis with CM10 or IMAC30 (but not Q10) protein chips detected a protein peak at m/z ~8570 released by both C57BL6 and hybrid embryos. No other peaks unique to the presence of the embryo were identified with this method. ESI mass spectrometry of tryptic digests of embryo-conditioned media identified a total of 20 proteins released during development from the zygote to blastocyst stage. Four proteins were expressed in at least 7 out of 8 cultures tested, one of these (lactate dehydrogenase B) was in all cultures. A further five proteins were in at least half of the cultures and 11 more proteins were in at least one culture. The expression of two of these proteins is essential for preimplantation embryo development (NLR family, pyrin domain containing 5 and peptidyl arginine deiminase, type VI). A further four proteins detected have roles in redox regulation of cells, and three others are capable of inducing post-translational modifications of proteins. This study shows the feasibility of ESI mass spectrometry for identifying the proteins secreted by the preimplantation embryo in vitro. This analysis identifies a range of targets that now require detailed functional analysis to assess whether their release by the embryo is an important property of early embryo development.

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