THE SPERM CENTRIOLE - ITS INHERITANCE, REPLICATION AND PERPETUATION IN EARLY HUMAN EMBRYOS

The inheritance, replication and perpetuation of the sperm centriole i n the early human embryo are reported, Both normal monospermic and abn ormal dispermic embryos (n = 127) were examined by transmission electr on microscopy. Centrioles were traced from fertilization to the hatchi ng blastocyst stage, The sperm proximal centriole is introduced into t he oocyte at fertilization and remains attached to the expanding sperm head during sperm nuclear decondensation, as it forms the male pronucl eus. A sperm aster is initially formed after the centriole duplicates at the pronuclear stage, At syngamy, centrioles occupy a pivotal posit ion on opposite spindle poles, when the first mitotic figure is formed , Bipolar spindles were found in the majority of embryos, while tripol ar spindles were seen in four dispermic embryos at syngamy, Two single centrioles were detected at two poles of two tripolar spindles, while two additional centrioles were located on the sides of a bipolar spin dle of a dispermic embryo, Sperm tails were detected near spindle pole s at syngamy and in later embryos, Typical centrioles showing the char acteristic pinwheel organization of nine triplets of microtubules were evident, During centriolar replication, the daughter centriole grows laterally from the parent and gradually acquires pericentriolar materi al (PCM), The two centrioles are surrounded by a halo of electron-dens e PCM, which nucleates microtubules, thus making it a typical centroso me, The usual alignment of diplosomes at right angles to each other wa s maintained, Centrioles were detected at all stages of embryonic clea vage from the 1-cell through 8-cell stages, right up to the hatching b lastocyst stage, They were closely associated with nuclei at interphas e, when they were often replicating, and were prominently located at s pindle poles during the first four cell cycles, In blastocysts, they w ere detected in trophoblast, embryoblast and endoderm cells respective ly, It is evident that the sperm centrosome is the functional active c entrosome in the human, while the female is inactive but may contribut e some centrosomal material to the zygote centrosome, It is very likel y that the paternal centriole is the ancestor of the centrioles in fet al and adult somatic cells.