Behaviour of the germ cell specific lamin through mammalian spermatogenesis as probed with monoclonal antibodies

Abstract

We had earlier identified a 60 kDa nuclear lamin protein (lamin_g unique to the germ cells of rat testis which was subsequently shown to be antigenically conserved in germ cells of grasshopper, rooster, frog and plants. We have now obtained eight monoclonal antibodies in mouse against this lamin_g antigen. While all the eight Mabs reacted with lamin_g antigen in an immunoblot analysis, only three Mabs (A₁₁C₇, A₁₁D₄, C₁F₇) showed strong reactivity in the immunofluorescence analysis of the germ cells. The Mabs A₁₁C₇ and A₁₁D₄ showed a slight cross-reactivity with rat liver lamin B. Indirect immunofluorescence analysis of pre-meiotic, meiotic and post-meiotic germ cells with Mabs have shown that while the lamin_g is localized in the lamina structures of spermatogonia and round spermatids, it is localized to the phase dense regions of pachytene spermatocytes which is in conformity with our previous observations using rabbit polyclonal antibodies. The localization of the antigen in the germ cells was also confirmed by immunohistochemical staining of the thin sections of seminiferous tubules. By immunostaining the surface spread pachytene spermatocytes, the antigen was further localized to the telomeric ends of the paired homologous chromosomes. Using anti-somatic lamin B antibodies, we have also demonstrated the absence of somatic lamins in meiotic and post-meiotic germ cells. The lamina structure of pre-meiotic spermatogonial nucleus contains both somatic lamin B and lamin_g as evidenced by immunofluorescence studies with two differently fluorochrome labelled anti-lamin B and anti-lamin_g antibodies. The selective retention of lamin_g in the pachytene spermatocytes is probably essential for anchoring the telomeric ends of the paired chromosomes to the inner nuclear membrane.