BOAR PROACROSIN EXPRESSED IN SPERMATIDS OF TRANSGENIC MICE DOES NOT REACH THE ACROSOME AND DISRUPTS SPERMATOGENESIS

Transgenic mice that express boar proacrosin were produced to examine mechanisms for targeting hydrolytic enzymes to the acrosome. A 2.3 kb transgene was constructed by ligating the cDNA for boar preproacrosin with the mouse protamine 2 promoter region. Six founder mice that inco rporated the transgene were identified by polymerase chain reaction an d Southern blot analysis. Northern blots indicated that the two male f ounders (Ac.2 and Ac.5) and male progeny from three female founders (A c.3, Ac.4, Ac.6) expressed the transgene mRNA in testis, but not in so matic tissues. In these transgenic animals boar proacrosin was detecte d by immunohistochemistry in condensing spermatids, but was not locali zed in the acrosome. This acrosomal targeting defect of the transgene product may result from its delayed expression during the later steps of haploid differentiation. Furthermore, both male founders and all Ac .4 and Ac.6 males were infertile, as determined by multiple matings fo r at least 2 months. Ac.3 males were either infertile or rarely transm itted the transgene to their offspring. The infertile males mated, pro duced copulatory plugs, and had seminal vesicle weights and testostero ne levels within the normal range. However, they produced significantl y fewer spermatozoa and had lower testis weights than controls. Althou gh the mitotic and meiotic phases of spermatogenesis appeared normal b y histological criteria, condensing spermatids were missing from most tubules, and multinucleated cells were present in the lumen of seminif erous tubules and in the epididymis. We hypothesize that boar proacros in which fails to reach the acrosome is activated in these transgenic mice, and that its proteolytic activity disrupts spermatogenesis durin g spermatid formation. (C) 1996 Wiley-Liss, Inc.