Cytoplasmic inclusions in Xenopus spermatogenic cells. ultrastructural and cytochemical analysis of the action of antimitotic agents on subcellular elements

Abstract

ABSTRACT The effects of vinblastine sulphate, alone and in combination with other antimitotic agents, were tested in vitro on testicular tissue from the anuran, Xenopus laevis. Treatment with vinblastine alone resulted in dissolution of spindle and intercellular bridge microtubules, but centrioles and sperm tail axonemes remained intact. In addition, no paracrystalloid inclusions typical of those reported in other cell types treated with vinblastine alone were observed in Xenopus spermatogenic cells. Such inclusions were formed, however, when vinblastine was administered in combination with colchicine, colcemid, or puromycin. Under optimal conditions, paracrystalloids were formed in all cells from primary spermatogonia to late spermatids. The maximum size paracrystalloid formed differed in different spermatogenic cell stages, with late primary spermatocytes containing the largest such inclusions, often averaging over 34 μ m3 each. Autoradiographic analysis of spermatogenic cells labelled with [3H]leucine prior to drug treatment indicated that some radioactive material was incorporated into paracrystalloids in all cell stages. Treatment of Xenopus spermatogenic cells with vinblastine and puromycin was also employed to investigate the possible relationship between paracrystalloid material and a naturally occurring spermatogenic cell inclusion, the chromatoid body, since previous experiments indicated that microtubule protein might contribute to the mass of this structure. It was found that under certain conditions, both paracrystalloids and giant chromatoid bodies can occur together in the same cell, each inclusion reaching a characteristic size independent of the other. This suggests that the two inclusions are aggregates of materials drawn from different subcellular precursor pools. In addition, autoradiographic analysis of isotope incorporation indicated that giant chromatoid bodies could be clearly labelled with tritiated amino acids, but not with [3H]uridine. The pattern of isotope incorporation observed in giant chromatoid bodies, coupled with their histochemical staining characteristics, rules out the possibility that these structures function as cytoplasmic nucleoli.