Testicular mitosis, meiosis and apoptosis in mink (Mustela vison) during breeding and non-breeding seasons

Testes of mink were compared between the breeding (March) and non-breeding seasons with the start (November) and cessation (May) of spermatogenic acti vity. Testicular mass and spermatozoa per gram testis were assessed. Percen tages of haploid (1C), diploid (2C) and tetraploid (4C) cells were monitore d using DNA flow cytometry and the proportions of somatic and spermatogenet ic cells were determined after selective labelling of somatic cells with a vimentin antibody. Apoptosis was examined by cell death detection ELISA, an d testosterone concentrations were measured with an enzyme-immunoassay. The significantly higher testis mass during the breeding period coincided with higher numbers of testicular spermatozoa per gram testis and peak of testi cular testosterone concentration in comparison with non-breeding periods. T he proportions of 1C, 2C and 4C cells showed corresponding strong differenc es between these periods with the maximum of 1C cells during breeding. The proportions of testicular cells in G2-M phase of mitosis were very low duri ng the period of peak spermatogenesis; they were markedly increased in the time of autumnal resumption in November but were even higher during testis involution in May. However, the meiotic transformation (1C:4C ratio) is max imal in March. The total as well as the relative proportions of spermatogen ic and somatic cells differed significantly not only between breeding and n on-breeding periods but also between the periods at the start and at the en d of active spermatogenesis. The intensity of apoptosis was also seasonally dependent, The highest level in March indicates a stimulated apoptosis eve n during the breeding period. In conclusion, the production of spermatozoa in mink is intensified by enlargement of gonads as well as enhanced efficie ncy of spermatogenesis during breeding. In this time, the testosterone conc entration and the meiotic transformation show high levels, but the mitotic activity of spermatogenic cells is already significantly diminished and an intensified apoptosis seems to precede the forthcoming testis involution af ter breeding. The results suggest that the regulation of seasonal testicula r activity is characterised by co-ordinated shifts in the relationships bet ween mitosis, meiosis, apoptosis and testosterone production. (C) 1999 Else vier Science B.V. All rights reserved.