Defining the neighborhoods that escort the oocyte through its early life events and into a functional follicle

Abstract

The ovary functions to chaperone the most precious cargo for female individuals, the oocyte, to allow the passage of genetic material to subsequent generations. Within the ovary, single oocytes are surrounded by a legion of granulosa cells inside each follicle. These two cell types depend upon one another to support follicle formation and oocyte survival. The infrastructure and events that work together to ultimately form these functional follicles within the ovary are unprecedented, given that the oocyte is fated like all other neighboring cells within the embryo prior to gastrulation. This review discusses the journey of the germ cell in the context of the developing female mouse embryo, with a focus on specific signaling events and cell-cell interactions that escort the primordial germ cell as it is specified into the germ-cell fate, migrates through the hindgut into the gonad, differentiates into an oocyte, and culminates upon formation of the primordial and then primary follicle.

Specific Deletion of AMP-Activated Protein Kinase (α1AMPK) in Murine Oocytes Alters Junctional Protein Expression and Mitochondrial Physiology

“…Both PKA and MAPK signal transduction pathways were observed to be involved in the junctional communication between the cumulus/granulosa cells and the oocyte and the somatic cells of the follicle. Communication is essential for the growing oocyte and has a role in supplying nutrients to the maturing oocyte [ 35 ]. Western-blot analyses have revealed a significantly reduced phosphorylation of a MAP protein, the extracellular signal-regulated kinases (ERK1/2) in ZP3-KO MII oocytes when compared with wild-type oocytes ( Fig.…”

Control of Oocyte Growth and Development by Intercellular Communication Within the Follicular Niche

“…These synchronously enter meiosis and progress to diplotene of prophase I where they become arrested (Borum 1961). By the time of birth, somatic pre-granulosa cells within the ovary have surrounded oocytes to generate primordial follicles, each consisting of one oocyte (~15 μm diameter in the mouse) enclosed by a single layer of squamous granulosa cells (Findlay et al 2015;Grive and Freiman 2015;Jorgensen 2013;Pepling 2012). However, for reasons not yet fully understood, a significant proportion of the oocyte population is lost by apoptosis during late embryogenesis (Ene et al 2013;Hutt 2015;Malki et al 2014), reducing the number of primordial follicles that form or remain at birth.…”

“…We will focus on postnatal growth and development of the oocyte and follicle. We refer readers to recent reviews for studies of pre-and perinatal stages (Findlay et al 2015;Grive and Freiman 2015;Jorgensen 2013;Pepling 2012). Experimental studies have revealed a dynamic bidirectional communication network that links the germ-line and somatic cells of the follicular niche and is governed by both direct cell-cell contact and paracrine signaling.…”

Epigenetic inheritance through the female germ-line: The known, the unknown, and the possible

“…Identifying the underlying mechanisms is particularly challenging in the case of the female, as relatively few oocytes can routinely be obtained for analysis. Nonetheless, because oocytes may remain dormant for up to 50 years in a woman before entering the growth phase that will lead to ovulation and fertilization, and the growth phase itself is a protracted process that requires ∼4 months in humans, they are potentially exposed for a very long time oocyte becomes enclosed by a small number of granulosa cells in a structure termed a primordial follicle [3,7,8]. The ovaries of a newborn female mouse harbor about 8000 primordial follicles [9], and those of a newborn girl about 1,000,000 [10].…”