Receptor for inositol 1,4,5-trisphosphate, a second messenger that mediates the release of intracellular calcium (By similarity). Involved in the induction of intracellular calcium increase in eggs during fertilization and in the formation of the fertilization envelope during oocyte maturation. In immature oocytes, distributed throughout the cytoplasm but not in the germinal vesicle (GV). During GV disintegration, expression is concentrated at the site where the GV was previously located. Following GV breakdown, expressed evenly throughout the egg cytoplasm. Expressed during oocyte maturation with levels remaining constant throughout this period (at protein level). The receptor contains a calcium channel in its C-terminal extremity. Its large N-terminal cytoplasmic region has the ligand-binding site in the N-terminus and modulatory sites in the middle portion immediately upstream of the channel region. Belongs to the InsP3 receptor family.