Behavior of the sperm centriole during sheep oocyte fertilization.

The proximal centriole of the sperm was incorporated into the oocyte, at fertilization and a small aster of microtubules formed in the neck region containing the centriole. At late pronuclear stage, the sperm astral microtubules were located in the narrow cytoplasmic space between the apposed pronuclei. One or two centrioles were observed in/or close to the sperm neck region lying between the apposed pronuclei. Short microtubules radiated from the pericentriolar material which surrounded the centrioles. These results indicate that the proximal centriole of the sperm is not lost after incorporation into the ooplasm, as it is usually thought for mammals, but persists through the first cell cycle of the zygote. Moreover, the centriole inherited from the sperm reproduces at the pronuclear stage and migrates to one pole of the first mitotic spindle.