In vitro recapitulation of female germ cell development: from specification to meiosis initiation

Germ cells are responsible for transmitting genetic information across generations, therefore their development is a highly complex and tightly regulated process. In humans, female germ cell development occurs primarily during the first and second trimesters of embryonic development. The earliest precursor, primordial germ cells (PGCs), is specified around the second week of development, after which these cells undergo multiple stages of maturation. Eventually, they differentiate into oocytes and remain dormant within primordial follicles. These follicles constitute the ovarian reserve, and since no new oocytes are produced after birth, there are currently no treatments for infertility resulting from oocyte defects. Induced pluripotent stem cells (iPSCs), which can give rise to all cell types of the body, can be generated from tissue samples such as blood, urine, and skin biopsies. In vitro gametogenesis aims to generate functional gametes from iPSCs, representing a promising therapeutic approach for individuals with germ cell deficiencies. Research has successfully directed iPSCs toward primordial germ cell-like cells (PGCLCs), mimicking the earliest stages of human germ cell development. However, further differentiation into functional oocytes remains a major challenge. This thesis identifies the essential role of extracellular matrix (ECM) components in supporting PGCLC differentiation and maintenance in 2D culture. Additionally, by introducing iPSC-derived germ cell precursors into a reconstructed fetal ovarian somatic niche, this work demonstrates the in vitro maturation of iPSC-derived germ cells and highlights the critical importance of maintaining germ cell fate for successful in vitro gametogenesis.<br>