The number of centrioles in insect sperm: A study in two kinds of differentiating silkworm spermatids

Abstract

The typical eupyrene and atypical apyrene cycles of sperm differentiation in Bombyx mori were studied, with special attention to centriole number and behavior. Contrary to other reports, there is always only one centriole in the differentiating and in the mature sperm, thus confirming our previous findings that insect sperm has one centriole at the base of the flagellum, in contrast to two centrioles found in many other groups of animals. This numerical difference is discussed in an evolutionary context.We have previously suggested that insect spermatids have only one centriole, while those of many other animal groups contain two centrioles (Friedlander and Wahrman, '66). However, it has been claimed that a second centriole exists in insect spermatids as well (Anderson, '67; Breland, Barker, Eddleman and Biesele, '68; Phillips, ' 7 0 ) , or has been assumed to exist although it has not been observed (Shay and Biesele, '68).These conflicting opinions in the number of centrioles in insect spermatids should, if possible, be resolved before further investigations into the problem of centriole multiplication during spermiogenesis are attempted. We therefore set out to determine by electron microscopy the number of centrioles, and, if it occurs, their mode of replication in the spermatids of the silkworm Bombyx mori. Tanaka ('55), using light microscopy, reported in the same insect four and two centrioles at each pole of the first and second meiotic divisions respectively, and two centrioles in each spermatid. If this is correct, centrioles must replicate twice during meiosis.The silkworm (like other Lepidoptera) produces two types of spermatozoa, eupyrene and apyrene. Eupyrene spermatozoa have the haploid number of chromosomes, while apyrene ones have none. The fine structural changes during the differentiation of these two types of sperm were studied to verify whether the differences be-J. MORPH., 134: 383-398.tween them have anything to do with the number of centrioles. The whole cycle of sperm differentiation was carefully searched for a second centriole that might exist in spermatids, disappearing before sperm differentiation is completed. We have found only one centriole throughout the whole development of the two kinds of spermatozoa. MATERIAL AND METHODSThe silkworm moths belonged to a univoltine race of Bombyx mori reared in our laboratory.Eupyrene spermatogenesis takes place jn the larva and ceases in the pupa, while apyrene spermatogenesis starts in the pupa and continues in the adult (Tazima, '64). Testes were removed from the fifth larval instar for the study of the former, and from the adult moth for the investigation of the latter. The gonads were fixed with 1.7% glutaraldehyde in 0.1 M phosphate buffer (pH 7.3) for two hours, postfixed in 1% OsO, in veronal buffer (pH 7.3) at 4°C for one hour, and embedded in Epon 812. The ultrathin sections were mounted on naked grids, stained for six minutes in a 50% ethyl-alcohol solution saturated with uranyl acetate, covered with carbon and observed in an R...

The Eupyrene-Apyrene Dichotomous Spermatogenesis of Lepidoptera. Organ Culture Study on the Timing of Apyrene Commitment in the Codling Moth

“…Eupyrene and apyrene spermatogenesis differ profoundly but their respective morphogenetic pathways are consistent, showing only minor variations among the diverse species. Although the general pattern of differentiation leading to the two types of spermatozoa have been worked out in some detail [4][5][6][7], the regulation of this dichotomy is still unclear [ 8]. 114 The conspicuous cytological events of the eupyrene spermatogenesis precede those of the apyrene spermatogenesis.…”

A Proximal Centriole-Like Structure Is Present in Drosophila Spermatids and Can Serve as a Model to Study Centriole Duplication

“…This centriole forms the flagellum and is therefore the homolog to the vertebrate distal centriole. During spermatid differentiation ( Figure 2A), a structure, called the centriolar adjunct (CA), appears transiently around this centriole (Friedlander and Wahrman 1971;Tates 1971;Tokuyasu 1975a,b;Wilson et al 1997). The centriolar adjunct is a very dynamic structure, which shrinks during spermatid differentiation to form a collar around the distal centriole and then disappears (Tates 1971;Wilson et al 1997).…”

Spermiogenesis of Eupyrene Sperm in Prepupae, Pupae, and Adults of Heliothis virescens (Lepidoptera: Noctuidae): an Ultrastructural Study

“…Previous studies on the testicular sperm of Lepidoptera were reported by Zylberberg (1963), Smith (1968), Phillips (1970a,b), Riemann (1970), Friedlander & Wahrman (1971), and Friedlander & Hauschtech-Jungen (1982) and by several studies reported in Baccetti (1970): Throughout the process of sperm maturation, the MDs are a prominent feature. In the youngest spermatid cysts, the cytoplasm contains numerous mitochondria.…”