Drosophila spermatogenesis is an excellent system in which to study the genetic analysis of the differentiation of germ cells from gonial precursor cells to motile sperm, including regulation of germ cell proliferation, meiosis, mitochondoria derivative formation, flagella formation and individualization

During late stages of spermatogenesis in Drosophila, a cyst of 64 syncytial spermatids elongates as the sperm axonemes are formed inside it. Then this elongated cyst is remodeled into individual sperm (Fig. 1) by a process called individualization. At the start of individualization actin cones assemble around the spermatid nuclei and then synchronously move from the heads to the tips of the tails (Fabrizio et al., 1998; Lindsley and Tokuyasu, 1980; Tokuyasu et al., 1972). As the actin cones move, a large accumulation of cytoplasm and vesicles, called the cystic bulge, forms around them. In the cystic bulge, the membrane of the cyst is remodeled to enclose each sperm axoneme. Individualization is especially interesting as a cell biological process because it requires an unusual amount of membrane remodeling using a welldefined actin structure. The fully elongated cyst can be up to 1800 μm long (Tokuyasu et al., 1972); therefore, this process requires the actin structures important for the process to move unidirectionally over a significant length. During the process, the bulk of the cytoplasm is discarded from the cell body. However, we have little information about the mechanism of this process. Drosophila spermatogenesis is an excellent system in which to study the genetic analysis of the differentiation of germ cells from gonial precursor cells to motile sperm, including regulation of germ cell proliferation, meiosis, mitochondoria derivative formation, flagella formation and individualization (Castrillon et al., 1993; Fuller, 1993; Kemphues et al., 1980). A large number of male sterile mutations that affect different aspects of spermatogenesis have been identified (Castrillon et al., 1993; Gonczy et al., 1992; Laughran et al., 1976; Lifschytz and Hareven, 1977; Lindsley and Lifschytz, 1972; Romrell et al., 1972; Wilkinson et al., 1974), and in these collections are mutants that affect individualization specifically (Castrillon et al., 1993; Fabrizio et al., 1998). In addition, the morphological stages of spermatogenesis have been well characterized at the ultrastructural level by electron microscopy (Lindsley and Tokuyasu, 1980; Tokuyasu et al., 1972) (A. D. Tates, PhD Thesis, Rijksuniversitei, Lieden, 1971). Moreover, a few 1805 Development 130, 1805-1816 © 2003 The Company of Biologists Ltd doi:10.1242/dev.00406