Spermatogenesis

Abstract

During spermatogenesis, pluripotent germ cells differentiate to become efficient delivery vehicles to the oocyte of paternal DNA. Though male and female germ cells both undergo meiosis to produce haploid complements of DNA, at the same time they also each undergo distinct differentiation processes that result in either sperm or oocytes. This review will discuss our current understanding of mechanisms of sperm formation and differentiation in Caenorhabditis elegans gained from studies that employ a combination of molecular, transcriptomic, and cell biological approaches. Many of these processes also occur during spermatogenesis in other organisms but with differences in timing, molecular machinery, and morphology. In C. elegans, sperm differentiation is implemented by varied modes of gene regulation, including the genomic organization of genes important for sperm formation, the generation of sperm-specific small RNAs, and the interplay of specific transcriptional activators. As sperm formation progresses, chromatin is -systematically remodeled to allow first for the implementation of differentiation programs, then for sperm-specific DNA packaging required for transit of paternal genetic and epigenetic information. Sperm also exhibit distinctive features of -meiotic progression, including the formation of a unique karyosome state and the centrosomal-based segregation of chromosomes during symmetric meiotic -divisions. Sperm-specific organelles are also assembled and remodeled as cells complete -meiosis and individualize in preparation for activation, morphogenesis, and the acquisition of motility. Finally, in addition to DNA, sperm contribute specific cellular factors that contribute to successful embryogenesis.

Developmentally programmed germ cell remodelling by endodermal cell cannibalism

“…Regardless of the role for PGC lobe elimination, our findings provide an additional example of the large-scale segregation of organelles or cytoplasmic components into and out of germ cells. Other examples include the pumping of cytoplasmic contents and organelles from support germ cells into enlarging oocytes in worms, flies and mice 35-37 , and the scuttling of cytoplasmic components that is needed to produce streamlined spermatozoa 38 . Thus, while cytoplasmic remodeling is a conserved feature of germ cells undergoing gametogenesis, our findings show that it can also occur in primordial germ cells.…”

CSR-1 and P granules suppress sperm-specific transcription in theC. elegansgermline

“…An exception is sperm-specific transcription, which instead depends on promoter sequences (Kulkarni et al, 2012;Merritt et al, 2008;Shim, 1999). In the fourth larval stage (L4), ∼40 germ cells in each of the gonad arms of the hermaphrodite undergo spermatogenesis and develop into 160 spermatids [reviewed by Chu and Shakes (2013)]. Mature sperm are then stored in spermathecae and used to fertilize the remaining germ cells that develop into oocytes.…”

Translational Control in the Caenorhabditis elegans Germ Line

“…Differentiated oocytes at the very proximal end complete meiotic progression with oocyte maturation are ovulated, fertilized and undergo the meiotic divisions (see Kim et al 2012 ). While sperm production happens in the hermaphrodite prior to oogenesis, spermatogenesis is a continuous process in the male with spermatocytes cellularizing before diakinesis (see Chu and Shakes 2012 ). Consequently, germ cells have to undergo two different types of cell divisions, mitosis of undifferentiated cells and meiosis of two sexspeci fi c differentiation programs, which occur in a spatially and temporally distinct manner while sharing a common cytoplasm.…”