The degeneration and disappearance of the centrioles during the development of the rat spermatozoon

Abstract

An intensive search has failed to locate a proximal centriole in the neck of the rat spermatozoon. This centriole is present in late spermatids but disappears before spermiation. The distal centriole also degenerates during spermiogenesis, though more gradually; it is no longer demonstrable by the time the spermatozoa reach the cauda epididymidis (except as a few remnants in a small minority of the cells). The rat spermatozoon is thus exceptional among mammals in being effectively acentriolate. The implications of this are discussed. Since there are no centrioles, the activity and control of the flagellum cannot depend on a centriole as a kinetic center. Furthermore, since no centrioles are introduced by the rat spermatozoon at fertilization, there can be no paternal inheritance of a formed centriole through the cytoplasm. And, in this species at least, paternal centrioles have no role in the first cleavage of the fertilized egg.

High incidence of multiple aster formation in vitrified-warmed bovine oocytes after in vitro fertilization

“…A high incidence of oocytes with multiple asters was notable in the vitrified group (Table 2, Fig, 1B). Except for rodents in which multiple cytoplasmic asters function as MTOC [22,23], each paternal centrosome organizes only a single aster and functions as an MTOC in many mammalian species. Conversely, parthenogenesis [39] and Taxol treatment to stabilize microtubules [19,40] can induce formation of cytoplasmic asters.…”

“…Experiment 3 was conducted to investigate whether the observed multiple asters were the cytoplasmic asters (maternal origin) or the fragmentation of sperm-aster (paternal origin). Based on the comparison of aster positioning between 5.5 and 8 hpi samples, the multiple asters frequently observed in the vitrified oocytes were considered not to be typical cytoplasmic asters of maternal origin reported in rodents oocytes [22,23], parthenogenetically activated horse oocytes [39], and Taxol-treated porcine [19] and human [40] oocytes. Because sperm cells lose most of the pericentriolar materials during spermiogenesis, sperm-derived centrosome can function as MTOC after recruiting centrosomal proteins dispersed in oocytes [18,21].…”

“…Conversely, rodent sperm lose their centrioles during spermiogenesis [21]. Hence, the oocytes use their own MTOC dispersed in the cytoplasm for aster formation; that is called cytoplasmic aster [22,23]. Timing of first cleavage in IVF-derived bovine oocytes is important for yield and quality of blastocysts, as oocytes cleaving earlier are more likely to become blastocysts [24,25], and the resulting blastocysts have higher cryosurvival potential [26] and higher pregnancy rates [24] than those cleaving later.…”

Contribution of spermatozoal centrosomes to the microtubule-organizing centre in Antarctic minke whale (Balaenoptera bonaerensis)

“…During fertilization in mammals, the centrosome introduced into the oocyte by the spermatozoon plays a critical role in assembly of the microtubule network that brings both male and female pronuclei to the center of the newly formed zygote, as reported in human (Simerly et al, 1995), rhesus monkey (Hewitson et al, 1996), rabbit (Pinto-Correia et al, 1994) and cattle (Navara et al, 1994). On the other hand, the paternal inheritance of MTOC does not occur in mouse (Schatten et al, 1985(Schatten et al, , 1986) and rat (Woolley & Fawcett, 1973) and the microtubule network developed from multiple cytoplasmic asters, instead of a single sperm aster, is involved in the migration of pronuclei. Rodent spermatozoa are lacking centrioles and the majority of pericentriolar proteins after spermiogenesis (Woolley & Fawcett, 1973;Manandhar et al, 1998Manandhar et al, , 1999.…”

“…On the other hand, the paternal inheritance of MTOC does not occur in mouse (Schatten et al, 1985(Schatten et al, , 1986) and rat (Woolley & Fawcett, 1973) and the microtubule network developed from multiple cytoplasmic asters, instead of a single sperm aster, is involved in the migration of pronuclei. Rodent spermatozoa are lacking centrioles and the majority of pericentriolar proteins after spermiogenesis (Woolley & Fawcett, 1973;Manandhar et al, 1998Manandhar et al, , 1999.…”