Summary. Adult female mice of an outbred strain and of the inbred C57BL strain were naturally or artificially inseminated with spermatozoa from 6-to 14-week-old males belonging to two inbred strains, C57BL and KE. Several hours after insemination, the females were killed and examined for the percentage of spermatozoa with morphologically abnormal heads found in the uterus and in the oviducal flushings. According to the degree of abnormality, misshapen spermatozoa were divided into five classes. In young KE males, large spermatozoa were observed and designated as diploid. The proportion of abnormal forms in the uterus depended on the strain and on the age of the males, and was highest in the group inseminated with spermatozoa from young C57BL strain mice. The proportion of abnormal spermatozoa in the oviducal flushings was greatly reduced, although positively related to the percentage of abnormalities in the uterus. This applied particularly to slight abnormalities, their percentage being about three times higher in the uterus than in the oviduct. Spermatozoa with severe abnormalities were either not found in the oviduct or their proportion was reduced more than ten times.The uterotubal junction appears to function as a barrier against morphologically abnormal spermatozoa, especially against severely deformed ones, although its selective action is not absolutely effective.
Sperm abnormalities were examined in the samples of the uterine contents collected after copulation. Male mice of the inbred C57BL/Kw (C57), CBA/Kw (CBA) and KE strains were tested at the ages of 6, 7, 8 and 10 weeks. Severely misshapen spermatozoa were produced by 6-week-old males of all strains: 30% of spermatozoa had 'thread-like' heads, devoid of Feulgen-positive material; the total proportion of abnormalities was lowest in CBA males. During maturation the percentages of abnormalities dropped rapidly and the proportion of drastically misshapen spermatozoa diminished in favour of less severe deformations. The frequency distribution of abnormal sperm types was strain specific for adult males but not for very young males. Large spermatozoa were seen in samples from young CBA and KE males (0.5-2%) and sporadically in 10-week-old CBA males. A negative relationship between body weight and the severity of abnormalities was seen for young, but not adult, males reared in litters of different size. No sperm deterioration was noticed in the first year of life of 5 KE males tested every 3 months until death, but a male surviving to 15 months had increased (38%) proportions of abnormal spermatozoa.
Sperm samples, recovered from various regions of the reproductive tract of male and female mice, were air dried, fixed for 2 min in acetic alcohol and stained with toluidine blue. Testicular sperm heads were deeply stained, while in the samples from the successive regions of caput epididymidis the proportion of stained heads gradually decreased and many of them were stained in their distal part only. Spermatozoa from the corpus and cauda epididymidis, vas deferens, uterus, oviduct and from the perivitelline space were colourless (except for one type of misshapen head). Sperm heads that had penetrated the vitellus became stained distally. Vas deferens sperm heads were fully stained after treatment with dithiothreitol for 30 min. We suggest that the inability to stain with toluidine blue is characteristic of sperm chromatin stabilized by disulphide bonds.
SUMMARYFour inbred strains of mice were used, differing in the total percentages of spermatozoa with abnormal heads (KE, 22·1%; C57, 26·4%; KP, 7·7%; CBA, 5·5%) and in the frequency distribution of abnormality types, as divided into four arbitrary classes. The most variable class 2 (narrow heads with canals inside the nuclear material) accounted for 47% of all abnormalities in KE strain, was common in CBA (29%) and almost missing in KP and C57 strains. F1 hybrids from the diallel crosses of these strains exhibited highly significant heterosis effects and significant reciprocal differences in the total percentage of abnormalities. The relative frequency of class 2 ranked in F1 hybrids in a similar order as calculated from the mid-parental values. After seven generations of backcrosses performed to introduce the Y chromosome from CBA to the genetical background of the KE strain, the total percentage of abnormalities was significantly reduced, although the relative proportion of class 2 was similar to that in KE strain. Also the Y chromosome from C57 strain, introduced into the genetical background of KE strain, caused a significant reduction of total abnormalities, but again the relative frequency of class 2 was not affected. It is concluded that the Y chromosome plays an important role in determining the total percentage of sperm head abnormalities, but does not seem to be involved in influencing specific abnormality types.
Three groups of eggs, intact, cumulus-free and zona-free, were inseminated in vitro with spermatozoa from C57BL/Kw male mice and incubated for 1\p=n-\2 h. In fixed, toluidine blue-stained preparations, spermatozoa surrounding the eggs or attached to them remained colourless, while sperm heads that had penetrated the vitellus were deeply stained. Those in the early stage with still condensed chromatin were used to evaluate the head shapes. In zona-free and in cumulus-free eggs, only severely misshapen sperm heads appeared at a lower frequency than in the samples used for insemination. The proportion of abnormal sperm heads of all classes was significantly lower in intact than in cumulus-free eggs and most severely abnormal forms were not found in intact eggs.The results suggest that abnormal spermatozoa are able to participate in fertilization, although their chances of penetrating the ova in vitro are greatly reduced in the presence of egg investments, especially of the cumulus.
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