Susan S. Suarez and Mariana F. Woflner, PNAS July 6, 2021 118 (27) e2108887118

Figure: (A) Human oviduct, with fimbriated portion of the infundibulum visible. The oviduct has been cut in midisthmus. A white box surrounds a COC (approximately to scale) being transported into the infundibulum. (B) A highly magnified view of the cumulus matrix of the COC interacting with oviductal cilia. Illustrations credit: Rose Gottlieb (artist).

A critical step in fertilization of eutherian mammals is the “pickup” of oocytes (eggs) by the oviduct (fallopian tube) from the surface of the ovary. In the ovary, each oocyte matures within a follicle, in which it is surrounded by supportive granulosa cells. As the time of ovulation nears, the granulosa cells close to the oocyte transform into cumulus cells, which begin secreting a hydrated elastic extracellular matrix (1). At ovulation, the oocyte plus its cumulus cells and their matrix—the cumulus–oocyte complex (COC)—is released from the ovary and must be pulled into the oviduct, vaulting over a gap between the surface of the ovary and the open end of the oviduct, the infundibulum. Failure of COC pickup can lead to failure of sperm to fertilize the oocyte or, worse, to ectopic implantation of an embryo outside of the uterus. In PNAS, Yuan et al. (2) demonstrate that the carpet of tiny motile cilia that coats the lining of the infundibulum is crucial to successful oocyte pickup and transport into the oviduct.

See: https://www.pnas.org/content/118/27/e2108887118