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  • Author: H Krzanowska x
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H. Krzanowska

Summary. Nonagouti (KP × C57BL)F1 hybrid females were artificially inseminated with a mixture of spermatozoa from males of the KE (nonagouti) and CBA (agouti) strains and the genotype of young was estimated by fur pigmentation. When KE and CBA spermatozoa mixed in the ratios of 1:1, 2:1 and 4:1 were inseminated after ovulation, 87%, 56% and 29% of progeny, respectively, were sired by CBA males, i.e. proportions of CBA progeny were significantly higher than ratios of CBA spermatozoa in the mixture. The surplus of CBA progeny was significantly less in females inseminated before ovulation, which may suggest that more rapid capacitation of CBA spermatozoa is partly responsible for their competitive advantage. In preparations from oviducal flushings of females killed 2–3 h after insemination, CBA spermatozoa (recognized by their shape) were found in similar proportions as in the inseminated mixture. There was therefore no evidence of their preferential selection at the uterotubal junction.

No competitive advantage of CBA spermatozoa occurred when they were inseminated with spermatozoa from males of the KE.CBA strain, congenic with KE but with the Y chromosome derived from the CBA strain. This indicates that genetic factors linked with the Y chromosome may influence competitive ability of spermatozoa.

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H Krzanowska and B Bilinska

Nuclei of mouse Sertoli cells were examined on air-dried toluidine blue-stained preparations to analyse factors influencing the aggregation of heterochromatin into chromocentres. For the CBA strain males tested at 1.3, 2, 3, 6, 9 and 12 months of age, mean numbers of heterochromatin bodies were 4.8, 2.4, 2.1, 1.8, 1.6 and 1. 4, respectively; two chromocentres predominated from 2 to 9 months of age. In the KE strain, heterochromatin aggregation was significantly accelerated; nuclei containing only one chromocentre were predominant from 6 months. The number of chromocentres did not change with the stages of the seminiferous cycle, and after 1 month of cryptorchid condition. Cryptorchidism resulted in disruption of spermatogenesis and Sertoli cell dysfunction, as demonstrated by the lack of immunohistochemically detectable androgen receptors. The difference in the number of chromocentres between KE and CBA Sertoli cells persisted after 3 days of in vitro culture, but unidentified cells with numerous chromatin bodies were also observed. Testing recombinant inbred strains indicates that at least two genes are involved in the difference in the number of chromocentres between progenitor KE and CBA strains; however, no correlations were found with 15 marker loci or with parameters linked to reproduction. Of the eight strains tested, AKR and C3H showed a 'CBA-like' chromocentre pattern; C57BL, B10.BR, B10.BR-Y(del) and KP were 'KE-like'; and BALB/c and DBA/2 were intermediate. The results showed that centromere aggregation in the Sertoli cell progresses throughout the life of a male in a strain specific manner; however, its functional significance remains unknown.

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

Summary. Spermatozoa of males from the inbred mouse strains, KE (albino) and CBA (agouti), are distinguishable by head shape and differ in quality: CBA spermatozoa show a lower percentage of abnormal heads and higher efficiency of fertilization. Aggregation chimaeras were produced to investigate whether these differences are intrinsic or extrinsic to spermatogenic cells. Among 24 overt chimaeras, 14 were males: 1 was sterile, 8 produced either KE or CBA spermatozoa, as recognized by shape and by progeny testing, and 5 (21%) were germ-line chimaeras. Both the level of abnormal sperm heads and the efficiency of fertilization of CBA and KE spermatozoa produced by chimaeric males (except two subfertile ones) were within the range characteristic for the respective strain. All 5 germ-line chimaeras, irrespective of their coat colour composition, produced about 98% KE and only 2% CBA spermatozoa, which indicated strong selection against CBA germ cells. However, mature CBA spermatozoa showed high competitive ability, because the proportion of agouti progeny (from the CBA component) sired by those males was significantly higher than the proportion of CBA spermatozoa, estimated from vaginal plug preparations after every mating. The fact that this difference was particularly striking for one chimaera with a preponderance of CBA somatic component may suggest some influences extrinsic to spermatogenic cells.

We conclude from this study that sperm head shape, the level of sperm abnormalities and fertilizing capacity are determined largely autonomously by genes acting in the germ cells. The internal environment created by foreign somatic cells exerts only minor modifications, unless there has been deterioration beyond the range of'normality'.

Keywords: mouse; chimaera; sperm abnormalities; sperm competition; germ cell selection

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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.