SOX3 is a transcription factor expressed within the developing and adult
nervous system where it mostly functions to help maintain neural
precursors. Sox3 is also expressed in other locations, notably
within the spermatogonial stem/progenitor cell population in postnatal
testis. Independent studies have shown that Sox3 null mice
exhibit a spermatogenic block as young adults, the mechanism of which
remains poorly understood. Using a panel of spermatogonial cell marker
genes, we demonstrate that Sox3 is expressed within the committed progenitor fraction of the undifferentiated spermatogonial pool. Additionally, we use a Sox3 null mouse model to define a potential role for this factor in progenitor cell function. We demonstrate that Sox3
expression is required for transition of undifferentiated cells from a
GFRα1+ self-renewing state to the NGN3 + transit-amplifying compartment.
Critically, using chromatin immunoprecipitation, we demonstrate that
SOX3 binds to a highly conserved region in the Ngn3 promoter region in vivo, indicating that Ngn3
is a direct target of SOX3. Together these studies indicate that SOX3
functions as a pro-commitment factor in spermatogonial stem/progenitor
cells.