The chromatoid body in spermatogenesis

Abstract

All germ cells throughout the animal kingdom contain cytoplasmic cloud-like accumulations of material called nuage. Polar bodies in Drosophila oocytes are probably the best known forms of nuage. In spermatogenic cells, the nuage is called chromatoid body (CB). In early spermatids of the rat, it has a diameter of 1-1.5 microm and a finely filamentous lobular structure. Typically, it is associated with a multitude of vesicles. It is first clearly seen in mid- and late pachytene spermatocytes as an intermitochondrial dense material. During early spermiogenesis it is seen near the Golgi complex and frequently connected by material continuities through nuclear pore complexes with intranuclear particles. In living cells, the CB moves around the Golgi complex and has frequent contacts with it. The CB also moves perpendicularly to the nuclear envelope, and even through cytoplasmic bridges to the neighbour spermatids. One of the major components of the CB is a DEAD-box RNA helicase VASA that belongs to a class of proteins thought to act as RNA chaperones. It is a general marker of all germ cells and best characterized in Drosophila. The mouse VASA homologue was recently used as a marker of sperm formation from embryonic stem cells. It becomes generally accepted that the CB with its associated structures constitute a mechanism of post-transcriptional processing and storage of several mRNA species that are shared between neighbour cells and used for translation when the genome of the spermatids becomes inactive.

The chromatoid body of male germ cells: Similarity with processing bodies and presence of Dicer and microRNA pathway components

“…The chromatoid body is suggested to be a mammalian counterpart of nuage on the basis of its structural features and protein composition (16). It is a finely filamentous, lobulated perinuclear granule located in the cytoplasm of mammalian postmeiotic round spermatids.…”

GDNF Signaling Regulates YBX1/mRNA Interactions in Mouse Spermatogonia.

“…This explains why global RNA production is high in undifferentiated spermatogonia, and decreases as they differentiate from type A to type B spermatogonia and further still in spermatocytes [8]. The distinctive nature of chromatin condensation during spermatogenesis compels germ cells to temporally separate transcription and translation, and it is through unique RNA binding proteins that this process of mRNA storage and regulation of translation timing occurs.…”

Genetic variation of copia suppression in Drosophila melanogaster

“…Among the 54 genes represented within this region, vasa stands to be a promising candidate because this protein is a critical component of the nuage-piRNA processing machinery. Vasa is a hallmark for germ cell development and belongs to a class of proteins that act as RNA chaperones (Parvinen, 2005). Vasa expression is restricted to testes and ovaries and null mutations of this gene results in complete sterility (Styhler et al, 1998).…”

“…During spermatocyte development in D. melanogaster, transcription ceases during early stages of spermatogenesis, with limited transcription observed after the first meiosis (see Parvinen, 2005 for a helpful review). Accordingly, the transcripts required for completion of spermatogenesis must be produced during the early stages and preserved for use in the later stages.…”

“…Accordingly, the transcripts required for completion of spermatogenesis must be produced during the early stages and preserved for use in the later stages. This kind of translational regulation is mediated by a special membrane-free microtubule-based structure called the nuage, also known as the chromatoid body in mammals (Parvinen, 2005). The nuage is comprised of a variety of germ cell related proteins with the most important being the vasa protein, a DEAD-box RNA helicase, which acts synergistically with the components from the piRNA system Piwi, AGO3, and Argonaut.…”