Male sterile alleles have identified many genes that function in male fertility. One problem associated with identifying genes that regulate the very earliest stages of spermatogenesis, spermatogonial stem cells (SSCs) and the stem cell niche, is that these genes often function in many organ systems and at early stages of development. Hence mutation of these genes may result in organismal lethality prior to adulthood. We have used the vinegar fly, Drosophila melanogaster, as a model to investigate genetic alleles that result in larval lethality but allow the animal to survive long enough to produce a testis with an observable stem cell niche.
We have phenotyped multiple alleles and discovered mutations that result in gain and loss of spermatogonial stem cells. Genetic complementation studies and genomic sequencing of these strains have allowed us to identify several new genes that regulate spermatogonial stem cell biology.
We found that the DNA helicase, Dna2, is required for maintenance of SSCs and that hypomorphic alleles of this gene allow animals to develop to adulthood but still result in loss of SSCs. Cell type specific RNA interference permitted us to determine that Dna2 is required within SSCs to prevent their loss but appears to be dispensable for niche function. The cyclin-dependent kinase, Cdk-7, was found to also be required for SSC maintenance but in this case appeared to function within the niche. We have sequenced several strains that have SSC / spermatogonial overproliferation phenotypes and are currently analysing their genomes to identify genes associated with these phenotypes.