Mark S. Fox

Human Pumilio-2 is expressed in embryonic stem cells and germ cells and interacts with DAZ (Deleted in AZoospermia) and DAZ-Like proteins

Early in development, a part of the embryo is set aside to become the germ cell lineage that will ultimately differentiate to form sperm and eggs and transmit genetic information to the next generation. Men with deletions encompassing the Y-chromosome DAZ genes have few or no germ cells but are otherwise healthy, indicating they harbor specific defects in formation or maintenance of germ cells. A DAZ homolog, DAZL (DAZ-Like), is found in diverse organisms, including humans and is required for germ cell development in males and/or females. We identified proteins that interact with DAZ proteins to better understand their function in human germ cells. Here, we show that PUM2, a human homolog of Pumilio, a protein required to maintain germ line stem cells in Drosophila and Caenorhabditis elegans, forms a stable complex with DAZ through the same functional domain required for RNA binding, protein–protein interactions and rescue of Pumilio mutations in flies. We also show that PUM2 is expressed predominantly in human embryonic stem cells and germ cells and colocalizes with DAZ and DAZL in germ cells. These data implicate PUM2 as a component of conserved cellular machinery that may be required for germ cell development.

Male infertility, genetic analysis of the DAZ genes on the human Y chromosome and genetic analysis of DNA repair

Many genes that are required for fertility have been identified in model organisms (Castrillon et al., 1993; Chubb et al., 1993; Mello et al., 1996). Mutations in these genes cause infertility due to defects in development of the germ cell lineage, but the organism is otherwise healthy. Although human reproduction is undoubtedly as complex as that of other organisms, very few fertility loci have been mapped (Reijo et al., 1995; Vogt et al., 1996; Aittomaki et al., 1995). This is in spite of the prevalence of human infertility, the lack of effective treatments to remedy germ cell defects, and the cost to couples and society of assisted reproductive techniques. Fifteen percent of couples are infertile and half of all cases can be traced to the male partner. Aside from defects in sperm production, most infertile men are otherwise healthy. This review is divided into two distinct parts to discuss work that: (i) led to the identification of several genes on the Y chromosome that likely function in sperm production; and (ii) implicates DNA repair in male infertility via increased frequency of mutations in DNA from men with meiotic arrest.

Germ Cell-Specific Genes and Posttranscriptional Regulation in the Testis

Ten to 15% of couples are infertile. One of the most common causes of infertility is defective spermatogenesis characterized by the production of few or no sperm (oligospermia and azoospermia, respectively). However, little is known of the molecular causes of spermatogenic failure. Current assessment of infertility is based on sperm counts and testicular biopsies with little molecular analysis, apart from Y chromosome analysis in some cases. Thus, we sought to examine whether microarray technology might enable us to profile gene expression in infertile men and define subclasses of spermatogenic failure with a biological basis. We performed microarray analysis on a small group of infertile men and then focused further on analysis of a subset of genes that encode RNA-binding proteins in the DAZ gene family and/or interact with proteins encoded by this family. In this chapter, we review these experiments and also discuss the target RNAs of these RNA-binding proteins in more detail.