Variations in subunit composition and modification have been proposed to regulate the multiple functions of cytoplasmic dynein. Here, we examine the role of the Drosophila ortholog of tctex-1, the 14-kDa dynein light chain. We show that the 14-kDa light chain is a bona fide component of Drosophila cytoplasmic dynein and use P element excision to generate flies that completely lack this dynein subunit. Remarkably, the null mutant is viable and the only observed defect is complete male sterility. During spermatid differentiation, the 14-kDa light chain is required for the localization of a nuclear "cap" of cytoplasmic dynein and for proper attachment between the sperm nucleus and flagellar basal body. Our results provide evidence that the function of the 14-kDa light chain in Drosophila is distinct from other dynein subunits and is not required for any essential functions in early development or in the adult organism.
INTRODUCTIONThe minus-end-directed microtubule motor cytoplasmic dynein has been implicated in a variety of cellular processes, including nuclear envelope breakdown, mitotic spindle assembly and orientation, chromosome movements, intracellular trafficking of organelles and mRNAs, and intraflagellar transport (reviewed in Karki and Holzbaur, 1999). The heavy chain subunit of dynein is known to provide ATPase and microtubule binding functions, and although more than one cytoplasmic dynein heavy chain has been identified, the major cytoplasmic dynein motor contains a homodimer of a single heavy chain. It remains unclear how this single cytoplasmic dynein motor is targeted to distinct organelles and cellular processes. One hypothesis is that the accessory intermediate, light intermediate, and light chain subunits of cytoplasmic dynein mediate its functional specialization. Consistent with this idea, in some eukaryotes these subunits are encoded by multiple genes that are differentially expressed and/or alternatively spliced as distinct transcripts in different tissues and cells (Gill et al., 1994;Pfister et al., 1996a;Bowman et al., 1999;Susalka et al., 2000;Tynan et al., 2000;Tai et al., 2001). In addition, the posttranslational modification of subunits may contribute to the heterogeneity of subunit composition in the dynein complex . Although the mutational analysis of the cytoplasmic dynein heavy chain has revealed a range of motor functions, the functional contribution of other individual subunits is not well understood.The present study addresses the function of the 14-kDa dynein light chain. This light chain was first identified as a cytoplasmic dynein subunit in mammalian brain (King et al., 1996a) and as an axonemal dynein subunit within the specialized inner arm dynein of the Chlamydomonas flagella (Harrison et al., 1998). In Drosophila, a molecular study of the 14-kDa light chain gene reported defective male fertility for hypomorphic alleles, but the nature of the mutations left unresolved the significance of the 14-kDa light chain in cytoplasmic dynein (Caggese et al., 2001). Sequence analysis...