Surfing the wave, cycle, life history, and genes/proteins expressed by testicular germ cells. Part 2: Changes in spermatid organelles associated with development of spermatozoa

Abstract

Spermiogenesis is a long process whereby haploid spermatids derived from the meiotic divisions of spermatocytes undergo metamorphosis into spermatozoa. It is subdivided into distinct steps with 19 being identified in rats, 16 in mouse and 8 in humans. Spermiogenesis extends over 22.7 days in rats and 21.6 days in humans. In this part, we review several key events that take place during the development of spermatids from a structural and functional point of view. During early spermiogenesis, the Golgi apparatus forms the acrosome, a lysosome-like membrane bound organelle involved in fertilization. The endoplasmic reticulum undergoes several topographical and structural modifications including the formation of the radial body and annulate lamellae. The chromatoid body is fully developed and undergoes structural and functional modifications at this time. It is suspected to be involved in RNA storing and processing. The shape of the spermatid head undergoes extensive structural changes that are species-specific, and the nuclear chromatin becomes compacted to accommodate the stream-lined appearance of the sperm head. Microtubules become organized to form a curtain or manchette that associates with spermatids at specific steps of their development. It is involved in maintenance of the sperm head shape and trafficking of proteins in the spermatid cytoplasm. During spermiogenesis, many genes/proteins have been implicated in the diverse dynamic events occurring at this time of development of germ cells and the absence of some of these have been shown to result in subfertility or infertility.

Genetics of germ cell development

“…During the first four embryonic divisions, the P granules segregate specifically into the cells of the P lineage. After these four divisions, P 4 , the precursor of all germ cells in the adult animal, divides to form the two germline founder cells Z2 and Z3. 7 P granule components are deposited maternally and are protected from degradation specifically in the germ cell lineage.…”

“…29,32 Despite the division between preformation and induction, fundamental similarities exist in the germ cell specification of worm, fly, and mouse. Each species sets aside a dedicated set of germ cell precursors -P 4 35 A maternally-inherited P granule protein, PIE-1, is required for this transcriptional silencing: in embryos derived from pie-1 mutants, zygotic transcripts are aberrantly present in the embryonic germ cell precursors, and the germline does not develop. 35,36 Ordinarily, the kinase complex Positive Transcription Elongation Factor b (PTEFb) recognizes and binds to the RNAPII C-terminal domain (CTD), phosphorylating serine 2 of the CTD to drive transcriptional elongation (Figure 2a).…”

“…We will focus on genetic regulation of these processes, leaving detailed discussion of the cell biological changes associated with migration and gametogenesis, and of the intricacies of meiosis, for other reviews. [1][2][3][4] …”

More Than a Simple Lock and Key Mechanism: Unraveling the Intricacies of Sperm-Zona Pellucida Binding

“…These HA binding sites are thought to be responsible for the sperm to penetrate the cumulus cell layer surrounding the oocyte (Berruti and Paiardi, 2011, Hermo, et al, 2010b, Hermo, et al, 2010c, Huszar, et al, 2007 Epididymal Transit  Lipid architecture is remodeled in preparation for the formation of membrane rafts during capacitation  Protein architecture is altered. Existing proteins are unmasked or undergo post-translational modifications, or alternatively novel proteins are integrated into the plasma membrane via epididymosomes and intraluminal fluid  Motility machinery is matured in preparation for acquisition of motility  Upon reaching the cauda epididymis spermatozoa are capable of a sinusoidal movement pattern characterized by a symmetrical tail motion at high frequency and low amplitude  Increase in ability to recognize and interact with zona pellucida (Cooper, 1986, Cooper and Orgebin-Crist, 1975, Dacheux and Paquignon, 1980, Jones, 1998, Jones, et al, 2007 Capacitation  Loss of specific decapacitation factors (DFs) allows freshly ejaculated spermatozoa to commence capacitation  Cholesterol efflux from the plasma membrane increases membrane fluidity promoting lateral movement of integral proteins, as well as the formation of membrane rafts  Influx of HCO3 -activates key signaling cascades whereby SACY stimulates cAMP and in turn PKA.…”

Sperm head shaping in ratites: New insights, yet more questions

“…Although conflicting evidence has been presented in the literature, morphological data supplied by conventional transmission electron microscopy, supplemented by the use of animal models, have implicated various cellular components and processes in nuclear (head) morphogenesis (Fawcett, et al, 1971;Hermo et al, 2010;Kierszenbaum et al, 2003Kierszenbaum et al, , 2004Kierszenbaum et al, , 2007Meistrich, 1993). These include the role of the forming acrosome ( Kierszenbaum et al, 2003( Kierszenbaum et al, , 2004( Kierszenbaum et al, , 2007Russell et al, 1991) inherent properties of the chromatin condensation process (Fawcett et al, 1971;Prisant et al, 2007;Nozawa et al, 2014;Zhuang et al, 2014) and the involvement of the manchette microtubules (Kierszenbaum, 2002;Meistrich, 1993;Meistrich et al, 1990;Nozawa et al, 2014;Russell et al, 1991Russell et al, , 1994Toshimori and Ito, 2003).…”