Anucleate Caenorhabditis elegans sperm can crawl, fertilize oocytes and direct anterior-posterior polarization of the 1-cell embryo

It has long been appreciated that spermiogenesis, the cellular transformati on of sessile spermatids into motile spermatozoa, occurs in the absence of new DNA transcription. However, few studies have addressed whether the phys ical presence of a sperm nucleus is required either during spermiogenesis o r for subsequent sperm functions during egg activation and early zygotic de velopment. To determine the role of the sperm nucleus in these processes, w e analyzed two C. elegans mutants whose spermatids lack DNA. Here we show t hat these anucleate sperm not only differentiate into mature functional spe rmatozoa, but they also crawl toward and fertilize oocytes. Furthermore, we show that these anucleate sperm induce both normal egg activation and ante rior-posterior polarity in the 1-cell C. elegans embryo. The latter finding demonstrates for the first time that although the anterior-posterior embry onic axis in C. elegans is specified by sperm, the sperm pronucleus itself is not required. Also unaffected is the completion of oocyte meiosis, forma tion of an impermeable eggshell, migration of the oocyte pronucleus, and th e separation and expansion of the sperm-contributed centrosomes. Our invest igation of these mutants confirms that, in C. elegans, neither the sperm ch romatin mass nor a sperm pronucleus is required for spermiogenesis, proper egg activation, or the induction of anterior-posterior polarity.