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In ejaculated semen from highly fertile bulls, abnormal head forms constitute 5 to 20% of the total number of sperm heads, while even higher percentages are commonly found in ejaculates from bulls with certain types of reduced fertility. Intranuclear spaces and a granular appearance of the nuclear chromatin were the major abnormalities observed in a high percentage of spermatozoa from two infertile bulls (McCosker, 1969).

The organization of the DNA and nuclear proteins forming the deoxyribonucleoprotein complex (DNP) in the chromatin of deformed sperm heads has received little attention. Previous studies have demonstrated that most morphologically abnormal sperm heads contain the same amounts of DNA as their normally shaped counterparts (Gledhill, 1966a). Defects in the binding of nuclear protein to DNA, which probably occur

Earlier studies evaluating the condensation of chromatin during spermiogenesis revealed that deoxyribonucleoprotein (DNP) becomes more resistant to thermal denaturation as the round spermatid elongates and assumes the shape of a mature spermatozoon (Ringertz, Gledhill & Darżynkiewicz, 1970). Unfortunately, only heterogeneously aged populations of cells, represented by spermatids in loosely defined categories and at differing intervals before release from the germinal epithelium, could be studied. Homogeneous preparations of spermatozoa leaving the testis were unavailable. Because the `testicular spermatozoa' group evaluated by Ringertz et al. (1970) was a mixture of spermatids and spermatozoa, it was not possible to determine if final stabilization of germ-cell DNP occurs during the latter phases of spermiogenesis or in the caput epididymidis. From the data for two bulls, Gledhill (1972) suggested that the thermal denaturation profile for spermatozoa removed from the caput epididymidis was different from that for cells obtained from the ductus deferens. He suggested, therefore,

Summary.

Data presented herein suggest that the normal changes of dnp which occur during spermiogenesis can be arrested or impeded and thereby result in biochemically immature spermatozoa. Possibly, the infertility exhibited by the bull under consideration was the consequence of such a defective (immature) spermatozoal dnp complex.

Summary.

Previously reported work has shown that a reduction in the rate of tritium-labelled actinomycin D ([³H]AMD) binding to spermatids and spermatozoa reflects the extent of the change in nuclear chromatin which occurs during spermiogenesis. Therefore, the kinetics of binding to the deoxyribonucleoprotein (DNP) of live, morphologically abnormal, testicular and ejaculated spermatozoa from five infertile and three control bulls have been studied by the use of quantitative autoradiography in order to examine suspected defects in the nuclear chromatin and particularly in the binding of nuclear protein to DNA.

Abnormally shaped heads bound up to sixteen times more [³H]AMD than did neighbouring normally shaped heads. There was no difference between the infertile and the control groups in the binding capacity of all types of spermatozoa. There was no single abnormal form which constantly bound more [³H]AMD than other forms although those malformed heads which tended to be round seemed generally to be the most heavily labelled. Testicular spermatozoa usually bound more [³H]AMD than did ejaculated spermatozoa. Ageing of ejaculated spermatozoa in vitro had no apparent effect on the binding of the isotope to nuclear chromatin. A pattern of labelling over the nuclei of elongated spermatids was noted which seemed to mimic the pattern of chromatin condensation of spermateliosis.

The greater availability of [³H]AMD binding sites in morphologically abnormal sperm heads suggests a defect in the condensation of nuclear chromatin. This defect has not been elucidated.