Meiosis is essential for sexual reproduction, and its specialized molecular and cellular programs have
been intensely studied in lower eukaryotes and mammals. In mammals, however, the transition from
mitotic spermatogonia into the meiotic program, termed meiotic initiation, has received little attention.
Meiotic initiation occurs during the preleptotene phase of meiotic prophase I, as these spermatocytes
replicate their DNA and prepare for meiotic recombination and segregation. Retinoic acid (RA) has been
proposed to serve as the ‘meiosis inducing substance.’ In the postnatal testis, although it is clearly required
for spermatogonial differentiation, our exciting preliminary data reveals RA is dispensable 8.6 days later
for meiotic initiation. Thus, the role of RA in meiosis has not been properly examined, and the true meiosis-
inducing factor(s) remain undefined. This proposal represents a new collaboration between the Geyer and
Schindler labs, who will work together to uncover the true role(s) for RA in meiosis. In Aim 1, we will identify
the specific requirement for RA in initiation and progression through meiosis to form haploid spermatids.
In Aim 2, we will employ a novel transgenic mouse model with synchronized spermatogenesis for
fluorescence-based isolation of millions of germ cells prior to and during meiotic initiation. Using this
unique resource, we will define and compare RA-mediated changes in gene expression at the
transcriptome (RNA abundance), translatome (translating RNAs), and proteome (protein abundance)
levels during meiotic initiation. The outcome of this work is identification of novel regulators of this critical
transition, and testis-specific proteins that are upregulated in preleptotene spermatocytes will represent
putative male contraceptive targets. Indeed, preleptotene spermatocytes represent an ideal cell type for
male contraceptive drug development, for two reasons: 1) they reside outside the blood-testis-barrier
(BTB), which is a significant barrier to drug delivery; and 2) they are distinct from the spermatogonial stem
cell (SSC) pool, and thus can be targeted without irreversibly damaging the male germline. The results
from this proposal will be foundational to defining the broader mechanistic relationship between RA and
meiosis that are essential for male fertility.