Monotremes, comprising solely of the echidna and platypus, are the oldest surviving mammalian lineage diverging from all other mammals approximately 190 million years ago. These animals have extraordinary reproductive and developmental biology being the only egg-laying mammals, yet most of the molecular mechanisms controlling these processes are unknown due to lack of appropriate genetic material.
Monotremes are seasonal breeders where during winter they alter their behaviours significantly to seek mates and undergo physiological changes such as males’ testes that swell six times their size during breeding season as they undergo spermatogenesis. Female adults have an ‘active’ and ‘inactive’ ovary, where only the active ovary produces eggs for reproduction and little is known about the function of the inactive ovary. For the first time, we have access to fresh tissue of juvenile echidnas, approximately one month of age, along with adult males from both inside and outside breeding season, and active and inactive adult ovary tissue. With these unique tissues we can better understand the molecular functions during breeding and development of gonads in monotremes.
Whole transcriptome sequencing was performed on testis from juvenile, out-of-breeding and in-breeding echidnas, as well as juvenile, active and inactive ovary. Our preliminary results reveal interesting patterns appearing through this novel data such as the juvenile testis gene expression being more similar to juvenile and adult ovaries than adult testis. Our results also show that olfactory receptors are highly upregulated in the inactive ovary compared to the active ovary, suggesting a role in olfactory oestrus activation during breeding season.
To our knowledge this is the first transcriptomic comparison of juvenile, adult and breeding season monotremes, which sheds light on important pathways involved in gonad development and their differing roles in monotremes.