Mechanisms of germ-soma communication during follicular growth.

Abstract

Communication between cells is essential for orchestrating tissue, organ, and whole-body cohesion. The communication can occur within the same cell (autocrine signaling), between neighboring cells (paracrine signaling), from distant cells (endocrine signaling), and between adjacent cells (juxtacrine signaling). Extracellular vesicle secretions, where messaging molecules like proteins, RNAs, and lipids are embedded in a membrane-enclosed particle released by the signaling cell, allow signaling to occur upon uptake and release of the cargo. Intercellular communications in synchrony between folliculogenesis and oogenesis involve both long-distance and short-distance messaging within the ovarian follicle, which is segmented into different cell types, with the oocyte lying at the center. Cells can generate extensions to increase the range of messaging by reaching out to more distant cells the so-called protrusion-based intercellular communication exemplified by tunneling nanotubes (TNTs), MT-nanotubes (MTNTs), microvilli, filopodia, and cytonemes. In mammalian oocytes, the filopodia from follicular cells that grow towards the oocyte is known as transzonal projections (TZPs). They accumulate large cargos, such as EVs, proteins and RNAs, at the tip creating the gametic synapses. These projections keep the oocyte and follicular cells connected and exchanging cytoplasmic content despite the apparent physical separation caused by the oocyte's zona pellucida. The protective and nurturing nature of follicular cells towards the oocyte, due to the presence of cellular interconnectivity within follicular cells and the oocyte, is conserved between species and is essential for communication, playing a crucial role in the development of a high-quality oocyte.