Localization and quantitative expression of the calcium-sensing receptor protein in human oocytes

Objective: To investigate the expression of the calcium-sensing receptor (CaSR) protein in human oocytes at the germinal vesicle (GV) and metaphase I (MI) and II (MII) stages. Design: Prospective study. Setting: Academic basic research laboratory and hospital-based fertility center. Patient(s): Immature and supernumerary mature oocytes (n = 118) excluded from intracytoplasmic sperm injection treatment. Intervention(s): Immunofluorescence and Western blot with a primary antibody against human CaSR. Confocal laser scanning microscopy (CLSM) together with quantitative image analysis used to measure the fluorescence intensity variations in oocytes at GV, MI, and MII stages. Main Outcome Measure(s): The CaSR expression pattern as evaluated by immunostaining in denuded oocytes and cumulus cells, CLSM, and three-dimensional image reconstructions; quantitative analysis at the equatorial plane of the oocyte. Result(s): We identified CaSR in human oocytes and cumulus cells. The fluorescence intensity within the oocyte varied with the developmental stage, with the greatest increase at the MI stage. Conclusion(s): The present study demonstrates for the first time the expression and localization of CaSR protein in human oocytes. Increased CaSR protein expression in the MI stage suggests that it may be involved in the regulation of human oocyte development and maturation.