The Caenorhabditis elegans spe-5 gene is required for morphogenesis of a sperm-specific organelle and is associated with an inherent cold-sensitive phenotype.

The nonrandom segregation of organelles to the appropriate compartment during asymmetric cellular division is observed in many developing systems. Caenorhabditis elegans spermatogenesis is an excellent system to address this issue genetically. The proper progression of spermatogenesis requires specialized intracellular organelles, the fibrous body-membranous organelle complexes (FB-MOs). The FB-MOs play a critical role in cytoplasmic partitioning during the asymmetric cellular division associated with sperm meiosis II. Here we show that spe-5 mutants contain defective, vacuolated FB-MOs and usually arrest spermatogenesis at the spermatocyte stage. Occasionally, spe-5 mutants containing defective FB-MOs will form spermatids that are capable of differentiating into functional spermatozoa. These spe-5 spermatids exhibit an incomplete penetrance for tubulin mis-segregation during the second meiotic division. In addition to morphological and FB-MO segregation defects, all six spe-5 mutants are cold-sensitive, exhibiting a more penetrant sterile phenotype at 16 degrees than 25 degrees. This cold sensitivity could be an inherent property of FB-MO morphogenesis.