Critical protein interactions for piRNA biogenesis

PROJECT SUMMARY P-element induced wimpy testis (PIWI)-interacting RNAs (piRNAs) are ~24-34 nt non-coding RNAs that have been discovered in diverse species. Repressing the expression of transposable elements via piRNAs represents a critical defense mechanism for germ cells to maintain genomic integrity. The piRNA biogenesis largely occurs

at nuage, the amorphous electron-dense granules with no limiting membrane in the cytoplasm. One specific type of nuage, intermitochondrial cement (IMC), is identified with uniquely clustered mitochondria and ribonucleoproteins as “cementing material” in embryonic germ cells, postnatal spermatogonia, and early-stage

spermatocytes. RNA-binding proteins such as PIWI family members are critical for piRNA biogenesis at IMC. Disrupting IMC formation or removing RNA-binding proteins from IMC often blocks spermatogenesis and impairs male fertility. Notably, none of the PIWI proteins possesses mitochondrial localization signal (MLS), and thus

they must rely on other proteins to be recruited to mitochondria or to functionally communicate with IMC. However, it remains a knowledge gap in how mitochondria recruit PIWI proteins to form IMC for piRNA biogenesis. To fill in this gap, in this R03 project, we will reveal how ASZ1, a mitochondrion-localized germ cell-specific protein,

recruits PIWI proteins to IMC for piRNA biogenesis (Aim 1) and subsequently impacts male germ cell development (Aim 2). Impact: Germ cells are essential carriers to pass genomic information across generations. This process requires properly generated piRNAs to maintain germline DNA integrity. By unveiling essential

protein interactions at IMC and defining their roles in IMC construction, piRNA biogenesis, and germ cell development, this project will generate novel knowledge about how the piRNA processing machinery is assembled to maintain genomic integrity, and thus critically inform the mechanistic causes of male infertility

related to piRNA biogenesis for targeted therapies. Findings from this project may also lead to a novel strategy for developing non-hormonal male contraceptives.