The sperm centriole: its inheritance, replication and perpetuation in early human embryos

Abstract

The inheritance, replication and perpetuation of the sperm centriole in the early human embryo are reported. Both normal monospermic and abnormal dispermic embryos (n = 127) were examined by transmission electron microscopy. Centrioles were traced from fertilization to the hatching blastocyst stage. The sperm proximal centriole is introduced into the oocyte at fertilization and remains attached to the expanding spermhead during sperm nuclear decondensation, as it forms the male pronucleus. A sperm aster is initially formed after the centriole duplicates at the pronuclear stage. At syngamy, centrioles occupy a pivotal position on opposite spindle poles, when the first mitotic figure is formed. Bipolar spindles were found in the majority of embryos, while tripolar 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 spindle of a dispermic embryo. Sperm tails were detected near spindle poles at syngamy and in later embryos. Typical centrioles showing the characteristic pin-wheel organization of nine triplets of microtubules were evident. During centriolar replication, the daughter centriole grows laterally from the parent and gradually acquires pericentriolar material (PCM). The two centrioles are surrounded by a halo of electron-dense PCM, which nucleates microtubules, thus making it a typical centrosome. The usual alignment of diplosomes at right angles to each other was maintained. Centrioles were detected at all stages of embryonic cleavage from the 1-cell through 8-cell stages, right up to the hatching blastocyst stage. They were closely associated with nuclei at interphase, when they were often replicating, and were prominently located at spindle poles during the first four cell cycles. In blastocysts, they were detected in trophoblast, embryoblast and endoderm cells respectively. It is evident that the sperm centrosome is the functional active centrosome in human, while the female is inactive but may contribute some centrosomal material to the zygote centrosome. It is very likely that the paternal centriole is the ancestor of the centrioles in fetal and adult somatic cells.

Diagnosis of abnormal human fertilization status based on pronuclear origin and/or centrosome number

“…Transmission electron microscopy (TEM) analysis revealed that centrosomes are duplicated at the PN stage, when male and female PNs are in close association [12,13]. Human oocytes lack centriolar structures [12] whereas human sperm have centrioles, and as a result, the zygotic centrosome must be derived from the sperm in human zygotes.…”

“…In humans, the centriole is transported by sperm into oocytes and the sperm centrosome forms a sperm aster after the centriole duplicates at the PN stage [12,13]. Therefore, the number of centrosomes represents the number of sperm that have entered into oocyte because human oocytes lack centriolar structures [12].…”

Centrosomes in fertilization, early embryonic development, stem cell division, and cancer

“…Most likely due to the difficulties to gather both centrioles of one centrosome or even both centrosomes at the same section plane in the voluminous ooplasm, double centrioles are not found at each pole of the first cleavage spindle. But afterwards, centrioles are then found at every stage of early embryo development (Sathananthan et al, 1996;Sathananthan, 1997). In bovine, centrioles are likewise paternally inherited, and organize the sperm aster after fertilization .…”

“…In bovine, centrioles are likewise paternally inherited, and organize the sperm aster after fertilization . Zygotes from humans, sheep and cows thus display centrioles at the spindle poles at first mitosis, although extensive electron microscopic studies have failed to find duplex centrioles in all spindle poles during the first cleavage of human zygotes (Sathananthan et al, 1991;Sathananthan et al, 1996;Santhananthan et al, 1997;Le Guen and Crozet, 1989). In sheep zygotes, the first cleavage spindle possesses two centrioles at one pole and only one centriole at the other pole, probably owing to difficulties to gather all centrioles at the same section plane (Crozet et al, 2000).…”

Primate models for assisted reproductive technologies

“…Using conventional and confocal epifluorescence microscopy of fixed oocytes and embryos, it has been well established that fertilization of rhesus oocytes requires a paternally derived centrosome (Sutovsky et al 1996, Wu et al 1996. The sperm centrosome is introduced into the oocyte during sperm incorporation where it is transformed into a zygotic centrosome, capable of nucleating microtubules (Simerly et al 1995, Sathananthan et al 1996. The microtubule-based 'sperm aster' is a radially arrayed three-dimensional structure that is found adjacent to and affixed to the sperm nucleus.…”