The retention and organization of HA in the extracellular matrix is mediated by HA-binding proteins, which include versican, tumor necrosis factor α-stimulated gene 6, pentraxin 3 and serum-derived members of the inter-α-trypsin inhibitor (IαI) family. The production of HA is controlled by hyaluronan synthase 2 (HAS2), which is highly expressed in cumulus cells shortly after the preovulatory surge of LH. In response to the preovulatory surge of LH, the cumulus cells start the synthesis of a large amount of hyaluronic acid (HA)-enriched extracellular matrix that is deposited into the extracellular spaces and causes the process of expansion. The resumption of meiosis is accompanied by an expansion of cumulus cells, a process that enables the detachment of the oocyte-cumulus complex from the follicle wall and its ovulation to the oviduct. This network includes major cellular protein kinases including protein kinase A (PKA), phosphoinositide-3-kinase/v-akt murine thymoma viral oncogene homolog (PI3K/AKT), mitogen-activated kinase 3/1 (MAPK3/1) and MAPK14 and downstream transcription factors including CREB, AP1, NRIP1, NR5A2 and CEBPB. The changes in the cumulus/granulosa cell transcriptome are under the control of a broad signaling network activated in follicular cells by the LH surge. Nevertheless, the LH-induced meiotic resumption is accompanied by a dramatic change in gene expression profiles in mural granulosa and cumulus cells. ![]() The resumption of meiosis is regulated inside oocytes by a post-translation mechanism and does not depend on the activation of genes in the oocyte itself. They only resume meiosis following the preovulatory surge of luteinizing hormone (LH). However, these meiotically competent oocytes still remain in the dictyate stage if they are retained within follicles. ![]() ![]() ĭuring the growth phase, the oocyte is arrested in the first meiotic prophase, but it gains full meiotic competence in several steps. In turn, the range of function of cumulus cells, including steroidogenesis, gene expression, extracellular matrix formation and metabolism, are modified by factors secreted by the oocyte. Both populations of granulosa cells fulfil different roles during follicle development: the mural granulosa cells are predominantly involved in the perception of signals from outside follicle, the production of steroid hormones and follicular rupture the cumulus cells provide nutrients and regulatory molecules for oocyte growth, final maturation and ovulation. In the antral follicles, the granulosa cells differentiate into two phenotypically distinct populations: the mural granulosa cells, lining the follicle wall and the cumulus cells, surrounding the oocyte in several layers. The development of mammalian female germ cells requires close contact and metabolic cooperation with the somatic granulosa cells.
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