Spermatogenesis: Analysis of Meiosis and Morphogenesis
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In this chapter, I hope to convince the reader that Drosophila spermatogenesis is an ideal system for the cytogeneticist. Spermatogenesis is relatively simple, dispensable for adult viability, and amenable to genetic, cell biological, and biochemical approaches. The stages of spermatogenesis are well defined, the cells are large, easily accessible, and easily identified. Because spermatogenesis initiates with a stem cell division, there is continuous production through the life of the fly. Therefore, a normal adult testis presents all of the stages of spermatogenesis as a spatio-temporal array (see Fig. 1 A ). Excellent and comprehensive reviews of the genetics of spermatogenesis and ultra-structure of wild-type spermatogenesis are available (1 ,2 ). In this introduction, I will review only the essential features needed to interpret the results of experiments performed according to the protocols given here.
Fig. 1. Phase-contrast microscopy of wild-type testes. The stages of spermatogenesis are easily visible with phase-contrast optics in gently squashed preparations. (A ) A whole wild-type testis, cut near the distal end, with most of the elongating spermatids spilled out through the cut. There is a temporal progression of cell types from very early stages at the apical end (top ) to nearly mature sperm at the distal end (bottom ), leading into the seminal vesicle (✻ ). (B –H ) Higher magnification of specific stages of spermatogenesis; (B ) polar spermatocytes. (C ) mature primary spermatocytes; (D ) part of a cyst in metaphase-anaphase I; (E ) part of a secondary spermatocyte cyst (meiotic interphase); (F ) a telophase II cyst; (G ) onion-stage spermatids (right) and comet stage of early spermatid elongation (left); (H ) part of a cyst late in elongation before individualization. (I –L ) Hoechst 33342 labeling of DNA in wild-type live squashes. (I ) Primary spermatocytes with decondensed chromosomes visible as three discrete regions in each nucleus; (J ) prophase of meiosis I, partially condensed chromosomes are visible; (K ) leaf blade stage, DNA is compact within the nucleus, faint staining of the mitochondrial DNA is seen in the Nebenkern; (L ) tightly clustered and fully shaped nuclei in nearly mature bundles of elongated spermatids, before individualization.
