Transcriptome Landscape Reveals Underlying Mechanisms of Ovarian Cell Fate Differentiation and Primordial Follicle Assembly

Abstract

Primordial follicle assembly in mammals occurs at perinatal ages and largely determines the ovarian reserve available to support the reproductive lifespan. The primordial follicle structure is generated by a complex network of interactions between oocytes and ovarian somatic cells that remain poorly understood. In the present research, using single-cell RNA sequencing performed over a time-series on mouse ovaries coupled with several bioinformatics analyses, the complete dynamic genetic programs of germ and granulosa cells from E16.5 to PD3 are reported for the first time. The time frame of analysis comprises the breakdown of germ cell cysts and the assembly of primordial follicles. Confirming the previously reported expression of genes by germ cells and granulosa cells, our analyses identified ten distinct gene clusters associated to germ cells and eight to granulosa cells. Consequently, several new genes expressed at significant levels at each investigated stage were assigned. Building single-cell pseudo temporal trajectories five states and two branch points of fate transition for the germ cells, and three states and one branch point for the granulosa cells were revealed. Moreover, GO and ClueGO term enrichment enabled identifying biological processes, molecular functions and cellular components more represented in germ cells and granulosa cells or common to both cell types at each specific stage. Finally, by SCENIC algorithm, we were able to establish a network of regulons that can be postulated as likely candidates for sustaining germ cell specific transcription programs throughout the investigated period.

Single‐cell RNA sequencing reveals the landscape of early female germ cell development

“…The third group TFs, like meiotic gene Dmrtc2 , mainly expressed in meiocytes, which may play an important role in meiosis progression. Similarly, Taf4b and Taf9b are highly expressed in late meiocytes (Figure 3A), which may play important roles in cyst break down and primordial follicle assembly 20 . Moreover, Taf4b null females are sterile, suggesting its essential role in oogenesis 21,22 …”

“…Similarly, Taf4b and Taf9b are highly expressed in late meiocytes ( Figure 3A), which may play important roles in cyst break down and primordial follicle assembly. 20 Moreover, Taf4b null females are sterile, suggesting its essential role in oogenesis. 21,22 To further dissect the differences in gene expression profiles, we identified 660, 856, 183, 138, 561, 609, and 568 differentially expressed genes among these seven clusters, respectively, and performed GO analysis of these genes.…”

Pathways coordinating oocyte attrition and abundance during mammalian ovarian reserve establishment

“…New data have suggested a potential role for ferroptosis in primordial follicle formation, as J.‐J. Wang et al (2019) have observed high messenger RNA expression of genes involved in ferroptosis in both granulosa and germ cells of mouse ovaries during perinatal development. While the roles of iron and ferroptosis in this process are not yet understood, the iron‐binding protein transferrin is known to be expressed in developing rodent and human follicles (Aleshire et al, 1989).…”