Taking care of Dad's DNA

Sexually reproducing animal species need to make two complementary types of gametes - sperm and eggs. The role of sperm is to deliver paternal genetic information to the egg. This process is dependent on the execution of meiosis and the packaging of haploid DNA inside the small sperm head. Maturing sperm undergo chromatin remodeling, which typically includes a transition from a histone-dependent organization to an organization dependent on sperm nuclear basic protein (SNBP) [1]. For example, protamines are thought to be required for the compact morphology of mammalian sperm nuclei [1]. Using Caenorhabditis elegans as a model system, a recent study by Chu et al. [2] used proteomics to identify conserved proteins essential for male meiosis and for the chromatin structure of sperm (Figure 1).Many genes in C. elegans that are essential for proper meiosis and germline development have been identified by genomic approaches. RNA interference (RNAi) induces the reduction of gene products and easily allows for the observation of loss-of-function phenotypes [3]. Several independent genome-wide RNAi analyses have identified a large number of genes associated with sterile phenotypes [4-8]. DNA microarray studies identified 1,343 sperm-enriched or sperm-specific genes, 1,652 oocyte-enriched or oocyte-specific genes and 3,144 germline-intrinsic genes [9,10]. Furthermore, to identify genes involved in chromosome morphogenesis and nuclear organization during meiosis, 192 germline-enriched genes whose expression patterns were similar to those of known meiosis genes were selected for an RNAi screen focusing on the germline phenotypes [11]. From this study 51 genes were identified for which RNAi-induced loss of function caused strong germline defects. Beyond microarray analysis [9,10], however, there were no gene profiles for function specifically in male fertility and sperm development. A proteomic approach to identifying the genes important for germline development was also lacking.