The sperm chemoattractant "allurin" is expressed and secreted from the Xenopus oviduct in a hormone-regulated manner

Recently, we cloned and sequenced the cDNA of allurin, a sperm chemoattractant isolated from the jelly of Xenopus laevis eggs [Proc. Natl. Acad. Sci. U.S.A. 78 (2001) 11205]. In this report, we demonstrate that allurin mRNA is expressed almost exclusively in the oviduct and that its expression is increased 2.5-fold by human chorionic gonadotropin over a 12-h period. Both dot blots and immunocytochemistry show that allurin is secreted from the upper two thirds of the oviduct that includes the pars recta and the proximal pars convoluta. Allurin appears to be deposited on the ciliated surfaces of luminal epithelial cells that come in direct contact with eggs as they move through the oviduct. Immune staining also demonstrates the presence of allurin in the serosal capsule of the oviduct. In contrast, allurin is not found within the tubular jelly-secreting glands or ducts that constitute a major portion of the oviduct wall. Therefore, we hypothesize that allurin is synthesized by nonciliated secretory cells in the luminal epithelium of the oviduct, is displayed on the ciliary layer and then mechanically mixed with jelly, and applied to eggs as they progress down the oviduct. This hypothesis is consistent with the fact that eggs progressing down the oviduct initially show evidence of allurin being incorporated into the J1 layer. Subsequently, allurin within J1 diffuses outward to J3 and eggs stored in the uterus now demonstrate a J3 localization of this chemoattractant.