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J. Styrna, J. Klag and K. Moriwaki

Summary. Two congenic strains of mice (control, B10.BR/SgSn; mutant, B10.BR-Ydel/Ms with partial deletion of the Y chromosome) were examined. In control males, 22·6% of spermatozoa had abnormal heads; in mutant males, there were 64·2%, the most common being heads with flat acrosomes. Sodium dodecyl sulphate polyacrylamide gel electrophoresis of mature sperm proteins, followed by acrosin assay and acrosome silver staining, revealed a reduced concentration of acrosin in acrosomal caps in 35·8% of the spermatozoa in mutant males. Electron microscope analysis showed that some of the round, early spermatids in the mutants had normally formed acrosomal caps but lacked the proacrosomal granule and had no, or only scarce, acrosomal material. These observations indicate that formation of the acrosomal cap is controlled separately from the synthesis of the acrosomal material and suggest that some factors linked on the Y chromosome are involved in the control of acrosome development.

Keywords: Y chromosome; abnormal spermatozoa; acrosomal development; mouse

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H. Krzanowska, J. Styrna and B. Wabik-Śliz

Recombinant inbred strains were developed from reciprocal crosses between two inbred strains of mice (CBA and KE) differing in sperm head shape, proportion of normal sperm heads (CBA, 95%; KE, 78%) and fertilization efficiency (CBA, 100% of fertilized ova; KE, 72%), to determine whether the indices of sperm morphology and function were correlated. The following parameters were analysed in recombinant inbred and progenitor strains: index of sperm head shape (head width in the middle of its length/head length), percentage of abnormal sperm heads, percentage of spermatozoa with progressive movements, efficiency of penetration of hyaluronic acid polymer (Sperm Select®) and percentage of fertilized ova after mating males from the tested strains with females from an outbred stock. For each investigated character, recombinant inbred strains, recombinant inbred EXCB and CBXE, could be divided into at least three categories: KE-like, CBA-like and intermediate, suggesting that in each case a minimum of two genes was involved. Recombinant strains derived from the reciprocal crosses of progenitor strains differed only with respect to the proportion of abnormal sperm heads, showing the involvement of the Y chromosome in determining this character. Penetration into Sperm Select was significantly correlated both with fertilization efficiency and sperm motility, while correlation with the proportion of normal spermatozoa did not reach the level of significance. However, there was a significant negative correlation of both sperm abnormalities and the incidence of supplementary spermatozoa in the perivitelline space with the index of sperm head shape. The results indicate that these characters are genetically linked, or that sperm heads with a lower width to length ratio are more prone to undergo deformations during spermiogenesis, and are less efficient in establishing contact with the vitellus after penetrating the zona pellucida.

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J Styrna, W Kilarski and H Krzanowska

Males of the B10.BR-Ydel mouse strain, with a deletion in the long arm of the Y chromosome, were backcrossed to CBA females to introduce the Ydel chromosome to the genetic background of the CBA mice. The CBA-Ydel males (sixth backcross generation) had similar symptoms to those previously described for B10.BR-Ydel males (deterioration of sperm quality and of efficiency of fertilization), but these effects were much less pronounced, showing a favourable influence of the CBA genetic background. The CBA-Ydel males produced only 12% severely misshapen spermatozoa, and mating with B10.BR females gave 100% successful fertilization. Although nearly all sperm heads were abnormal (92% versus 6% in control males), most of the spermatozoa (76%) had deformation only in the acrosomal part, that is, flat heads, which were not found in the control males. These abnormalities were analysed in detail. As shown by differential staining, the acrosomes of the spermatozoa with flat heads were deformed; 18% of these acrosomes looked damaged, and often contained a vesicle, which stained in a similar way to the acrosome but lacked the reaction for acrosomal proteinase. Electron microscopy of testis sections revealed that deformations appeared already in round spermatids as distortion of the acrosomal vesicle and asymmetrical position of the acrosomal granule; in many elongating spermatids the proximal end had a flat or concave shape, and the acrosomes contained a translucent vesicle. It is possible that the genes that are missing in the Yq deletion have some important regulatory function in the course of spermiogenesis, which may explain the various sperm defects observed in Y-del males.