Drosophila Suppressor of Hairy-wing [Su(Hw)] is a polydactyl zinc-finger transcription factor that functions as an insulator, activator and repressor protein. Su(Hw) is nearly ubiquitously expressed in all tissues throughout development. One exception is the testis, wherein Su(Hw) is down-regulated mid-way through spermatocyte growth, at a time prior to the onset of the testis-specific transcriptional program. These observations prompted us to test whether Su(Hw) has a role in spermatogenesis. We found that loss of Su(Hw) causes age-dependent male sterility that is accompanied by defects in sperm production. The su(Hw) mutant testes are characterized by formation of bulges at the posterior end, which are filled with individualized sperm. Concomitant with pre-mature sperm release within testes, seminal vesicles are small. Based on the timing of Su(Hw) expression and its genome-wide localization within Lamin-associated domains, we hypothesized that Su(Hw) contributes to the developmental program in the testis by conferring transcriptional repression of testis-specific cluster genes in early spermatogenesis. This postulate was tested using microarray analysis to compare gene expression in su(Hw)+/+ and su(Hw)-/- testes. Data obtained from these studies revealed that few (2%) of ~300 mis-regulated genes correspond to genes inside the testis clusters. Instead, the majority of these genes correspond to de-repressed neuronal genes, reminiscent of the transcriptional effects associated with Su(Hw) loss in the ovary. Our working model is that expression of one or more Su(Hw) target genes is altered in su(Hw)-/- testes, which interferes with normal spermatogenesis. Current investigations are focused on identifying genes responsible for this block.