Drosophila spermatogenesis as a model system* (original) (raw)
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Molecular biology of sperm head shaping
Society of Reproduction and Fertility supplement, 2007
The shaping of the mammalian sperm involves the elongation and condensation of the spermatid nucleus, the development of the acrosome, and the transient appearance of the microtubular manchette. F-actin-containing ectoplasmic hoops of Sertoli cells embrace the upper third of the spermatid head during elongation. During acrosomal biogenesis, proacrosomal vesicles derived from the Golgi apparatus, dock and fuse along the acroplaxome, an F-actin/keratin 5-containing cytoskeletal plate. The acroplaxome consists of a bent plate and a marginal ring encircling the spermatid nucleus. It anchors the developing acrosome to the spermatid nucleus. The manchette, consisting of a perinuclear rings with inserted microtubules, lies subjacent to the marginal ring of the acroplaxome. During spermatid elongation, the two overlapping rings reduce their diameter to fit, in a sleeve-like fashion, the decreasing diameter of the spermatid nucleus. The acroplaxome may provide a planar scaffold to modulate e...
Cytoskeleton localization in the sperm head prior to fertilization
Reproduction, 2005
Three major cytoskeletal proteins, actin, tubulin and spectrin, are present in the head of mammalian spermatozoa. Although cytoskeletal proteins are implicated in the regulation of capacitation and the acrosome reaction (AR), their exact role remains poorly understood. The aim of this study was to compare the distribution of the sperm head cytoskeleton before and after the AR in spermatozoa representing a range of acrosome size and shape. Spermatozoa from the human and three rodents (rat, hamster and grey squirrel) were fixed before and after the AR in appropriate medium in vitro. Indirect immunofluorescent localization of cytoskeletal proteins was undertaken with antibodies recognizing actin, spectrin and a-tubulin. Preparations were counterstained with propidium iodide and examined by epifluorescent and confocal microscopy. Our results clearly demonstrated changes in localization of cytoskeleton during the AR, mainly in the apical acrosome with further changes to the equatorial segment and post-acrosomal regions. The pattern of cytoskeletal proteins in the sperm head of all the species was similar in respect to various sub-compartments. These observations indicated that the sperm head cortical cytoskeleton exhibits significant changes during the AR and, therefore, support the image of cytoskeletal proteins as highly dynamic structures participating actively in processes prior to fertilization. Reproduction (2005) 130 61-69 q 2005 Society for Reproduction and Fertility Cytoskeleton of the sperm head 69 www.reproduction-online.org Reproduction (2005) 130 61-69
Centrioles to basal bodies in the spermiogenesis of Mastotermes darwiniensis (Insecta, Isoptera)
Cell Motility and the Cytoskeleton, 2009
In addition to their role in centrosome organization, the centrioles have another distinct function as basal bodies for the formation of cilia and flagella. Centriole duplication has been reported to require two alternate assembly pathways: template or de novo. Since spermiogenesis in the termite Mastotermes darwiniensis lead to the formation of multiflagellate sperm, this process represents a useful model system in which to follow basal body formation and flagella assembly. We present evidence of a possible de novo pathway for basal body formation in the differentiating germ cell. This cell also contains typical centrosomal proteins, such as centrosomin, pericentrin-like protein, g-tubulin, that undergo redistribution as spermatid differentiation proceeds. The spermatid centrioles are long structures formed by nine doublet rather than triplet microtubules provided with short projections extending towards the surrounding cytoplasm and with links between doublets. The sperm basal bodies are aligned in parallel beneath the nucleus. They consist of long regions close to the nucleus showing nine doublets in a cartwheel array devoid of any projections; on the contrary, the short region close to the plasma membrane, where the sperm flagella emerge, is characterized by projections similar to those observed in the centrioles linking the basal body to the plasma membrane. It is hypothesized that this appearance is in connection with the centriole elongation and further with the flagellar axonemal organization. Microtubule doublets of sperm flagellar axonemes are provided with outer dynein arms, while inner arms are rarely visible. Cell Motil. Cytoskeleton 66: 248-259, 2009. '
Cells, 2018
Centrioles are ancient subcellular protein-based organelles that maintain a conserved number and structure across many groups of eukaryotes. Centriole number (two per cells) is tightly regulated; each pre-existing centriole nucleates only one centriole as the cell prepares for division. The structure of centrioles is barrel-shaped, with a nine-fold symmetry of microtubules. This organization of microtubules is essential for the ancestral function of centriole-cilium nucleation. In animal cells, centrioles have gained an additional role: recruiting pericentriolar material (PCM) to form a centrosome. Therefore, it is striking that in animal spermatozoa, the centrioles have a remarkable diversity of structures, where some are so anomalous that they are referred to as atypical centrioles and are barely recognizable. The atypical centriole maintains the ability to form a centrosome and nucleate a new centriole, and therefore reveals the most rudimentary structure that is needed for centriole function. However, the atypical centriole appears to be incapable of forming a cilium. Here, we propose that the diversity in sperm centriole structure is due to rapid evolution in the shape of the spermatozoa head and neck. The enhanced diversity may be driven by a combination of direct selection for novel centriole functions and pleiotropy, which eliminates centriole properties that are dispensable in the spermatozoa function.
The sperm centriole: its inheritance, replication and perpetuation in early human embryos
Human Reproduction, 1996
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 pinwheel 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 8cell 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 This paper is dedicated to Theodore Boveri for his brilliant theory on fertilization in 1887 and 1901. (Paper was presented at the 2nd International Malpighi Symposium, Rome, 1995.) centrosome is the functional active centrosome in the 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.
Molecular Basis of Sperm Flagellar Axonemes: Structural and Evolutionary Aspects
Annals of the New York Academy of Sciences, 2007
The axonemes serve as motile machineries in sperm flagella. Although atypical axonemal structures are observed in some cases, 9 + 2 microtubule structure of the axoneme is predominant in many organisms. Several structures are bound to these microtubules and comprise a highly organized protein network. Extensive proteomic analysis of the axonemes has led to find several repeats, domains, and motifs in axonemal proteins. Molecular comparison of subunit composition of axonemal substructures between the ascidian Ciona intestinalis and the green algae Chlamydomonas reinhardtti leads to an intriguing molecular aspect concerning the evolution of intracellular functional complex: The architecture of the axonemes has been well conserved through evolution, but the molecular structure of each axonemal component is not always conserved. In light of domain structure in the axonemal proteins, substructures like outer arm dynein and radial spoke contain a set of domain structures, although some domain-containing subunits are different between these two organisms. Thus, conservation of protein domains within a substructure seems to take precedence over that of each protein ("module-dominant conservation"), which may ultimately result in morphological and functional conservation of the axonemes through evolution.
Centriole Remodeling during Spermiogenesis in Drosophila
Graphical Abstract Highlights d Drosophila sperm centrioles are structurally modified during spermiogenesis d The proximal centriole-like (PCL) is an atypical centriole missing microtubules d Atypical sperm centrioles are essential for embryogenesis d Poc1 enrichment during spermiogenesis is essential for normal embryogenesis