Community Research and Development Information Service - CORDIS

New knowledge on testis development, and cell proliferation and apoptosis of germ cells and somatic cells in testis

Germ and Sertoli cell proliferation and apoptosis in salmon testis under different experimental conditions.

The incidence of apoptosis was high in animals that had been recruited into maturation but low in animals there were immature, irrespective of the light regimen the animals were exposed to. We conclude that changes in the incidence of apoptosis are secondary to changes in proliferation activity and do not reflect a direct effect of photoperiod manipulation.

An antiserum against phosphorylated histone H3 (pH3; a protein present during the G2-phase and up until in the M-phase of the cell cycle) was found suitable as mitosis marker for salmon testis and was used on Atlantic salmon testis sections to study germ cell proliferation. We have shown that a very low incidence of proliferation was associated with LL-induced inhibition of testis growth. The limited numbers of cells that still were proliferating were mostly single spermatogonia and (rarely) Sertoli cells or extratubular somatic cells. In samples from LL-stimulated males collected in February and March, on the other hand, immunoreactive nuclei either belonged to single spermatogonia, or to small groups of spermatogonia. Moreover, Sertoli cell nuclei were labelled, indicating entry into the growth phase.

Continued development resulted in the appearance of large groups of labelled cells, reflecting that the size of proliferating germ cell clones increased. This demonstrates the progress through the consecutive rounds of mitosis that is typical of the initial growth phase of the maturing testis. No differences were observed between maturing NL and LL males. However, a very interesting observation made in some samples of the NL group at the beginning of recruitment into maturation was that in February and March, a relatively high incidence of proliferation was found, predominantly single spermatogonia and Sertoli cells, while circulating androgen levels were still low. This indicates that the initial steps of proliferation are stimulated by another signal than androgens, possibly FSH. Subsequent to this initial step, however, elevated proliferation and 11KT plasma levels always were positively correlated in maturing animals in both NL- and LL-treated fish.

We conclude that the initiation of spermatogenesis (ie. expansion of early spermatogonia) takes place while androgen levels are still low, possibly triggered by FSH, while the rapid spermatogonial proliferation leading to the generation of large cysts, is associated with high 11KT levels. This is supported by direct experimental evidence in other species, where treatment with 11KT in vivo (Cavaco et al., 2001) or in vitro (Miura et al., 1991) triggered spermatogonial proliferation. Altogether, the analysis of proliferation on the cellular level proved to be a very strong parameter in the evaluation of recruitment into maturation.

Reported by

Follow us on: RSS Facebook Twitter YouTube Managed by the EU Publications Office Top