SPERMATOGENESIS is a complex developmental process that occurs in several phases. A large number of genes have been identified that are expressed during spermatogenesis1,2, but the biological significance of many of these is not yet known. We have used gene targeting to selectively eliminate the transcription factor CREM (cyclic AMP-responsive element modulator), which is thought to e important for mammalian spermatogenesis3–5. Male mice deficient for all CREM proteins are sterile, as their developing spermatids fail to differentiate into sperm, and postmeiotic gene expression in the testis declines dramatically. The cessation of sperm development is not accompanied by decreases in the levels of follicle-stimulating hormone or testosterone. Our findings indicate that the CREM gene is essential for spermatogenesis, and mice deficient for this transcription factor could serve as a model system for the study of idiopathic infertility in men.

Severe impairment of spermatogenesis in mice lacking the CREM gene

Sperm from mice carrying a targeted mutation of the acrosin gene can penetrate the oocyte zona pellucida and effect fertilization.

Acrosin (ACR), a serine proteinase located in the acrosome of the sperm, has been presumed to be involved in the recognition and binding of the sperm to the zona pellucida of the ovum and the sperm penetration through the zona pellucida. To examine the function of acrosin in vivo, we have generated mice carrying a mutation at the acrosin locus (Acr) through targeted disruption in embryonic stem (ES) cells. One chimeric male and female transmitted the targeted gene through their germ line. Homozygous Acr-/- mice are fertile and yield litters comparable in number and size to those of Acr+/+ mice. These data show that sperm of the homozygous Acr-/- mice are able to penetrate the zona pellucida, fertilize the ovum, and produce viable offspring. However, spermatozoa lacking acrosin protein show a delayed fertilization. One chimeric male which contained the targeted gene in 20% of its sperm transmitted only the Acr+ allele to its progeny. Furthermore, in vitro fertilization with equally mixed sperm cells of Acr+/+ and Acr-/- mice resulted in fertilization only with the Acr+ sperm cells. Incubation of oocytes with Acr+ or Acr- sperm show that the Acr+ sperm are faster to fertilize the oocytes than the Acr- sperm cells. These results suggest that Acr- sperm have a selective disadvantage when they are in competition with Acr+ sperm.

Spermatozoa lacking acrosin protein show delayed fertilization.

The roles of acrosomal matrix proteases in sperm-zona pellucida interactions have long been one of the most puzzling questions in mammalian fertilization. Of the acrosomal proteases identified, acrosin exhibits two distinct activities: (i) an enzymatic activity as a trypsin-like serine protease; and (ii) a lectin-like carbohydrate-binding activity. Thus, acrosin has been postulated to function both in the limited proteolysis of the zona pellucida, and in the maintenance of binding of acrosome-reacted sperm to the zona. However, analysis of acrosin-deficient mouse sperm demonstrates that this protein is not essential for sperm-zona pellucida interactions, including the sperm penetration of the zona pellucida. Acrosin is presumably involved in the limited proteolysis and/or processing of other proteins in the acrosome and on the membranes during the acrosome reaction at least in the mouse, although the serine protease system in mouse sperm is very different from those in sperm of other rodent species. It is concluded that membranous proteases rather than acrosomal proteases may play an important role(s) in the sperm-zona pellucida interactions.

/pdf/role-of-acrosomal-matrix-proteases-in-sperm-zona-pellucida-25489jivcl.pdf

Role of acrosomal matrix proteases in sperm–zona pellucida interactions

Interactions between zona pellucida glycoproteins and sperm proacrosin/acrosin during fertilization.

Mouse preproacrosin: cDNA sequence, primary structure and postmeiotic expression in spermatogenesis

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Mouse preproacrosin: cDNA sequence, primary structure and postmeiotic expression in spermatogenesis