Oral Presentation ESA-SRB-ANZBMS 2024 in conjunction with ENSA

Cardiac troponin I TNNI3 is a contemporary pregranulosa cell marker of primordial follicle activation. (#165)

Emily R Frost 1 2 , Brendan Crow 1 2 3 , Güneş Taylor 2 , Robin Lovell-Badge 2 , Jessie M Sutherland 1 3
  1. School of Biomedical Science & Pharmacy, College of Health, Medicine and Wellbeing, University Of Newcastle, Callaghan, NSW, Australia
  2. Stem Cell Biology and Developmental Genetics Lab, The Francis Crick Institute, London, United Kingdom
  3. Women's Health Research Program, Hunter Medical Research Institute, Newcastle, NSW, Australia

Primordial follicle activation is the first step towards oocyte maturation and essential for female fertility. There is a finite number of primordial follicles within the ovary, each consisting of a single oocyte and surrounding layer of pregranulosa cells. Follicle activation involves distinct morphological and molecular changes in both pregranulosa cells and oocytes. However, the signal initiating activation, and even the cell-type responding to this signal, remain unidentified. In early postnatal development, the primordial follicles of the inner ovarian medulla activate in relative synchrony in a process called first wave activation. We aimed to to identify a putative gene signature of activating pregranulosa cells by investigating the transcriptomic changes during this first wave in mice.

To profile the transcriptomic dynamics of first wave activation, single-cell RNA sequencing (scRNAseq) and integrated bioinformatics was conducted on C57BL/6 mouse ovaries at embryonic day 18.5, post-natal day 4, and post-natal day 7. We performed subcluster analysis on only granulosa cell clusters to identify more discrete gene expression changes across these clusters and describe a putative gene signature of activating pregranulosa cells. Finally, to validate the functional involvement of these genes, we queried the candidates in an established model of precocious and aberrant follicle activation, the Cdkn1b/p27kip1 null mice.

In this study we identified a putative gene signature of activating pregranulosa cells. Expression of one of these genes, Cardiac troponin I (Tnni3) was also upregulated in the Cdkn1b/p27kip1 null model of dysregulated activation. Furthermore, we confirmed functional expression of TNNI3 was significantly greater (p=<0.0001) in granulosa cells of activated follicles when compared to the pregranulosa cells of dormant follicles.

This study highlights TNNI3 as a key marker for activating pregranulosa cells and underscores the importance of pregranulosa cell changes in initiating primordial follicle activation.