Chromatoid body

A chromatoid body is a dense structure in the cytoplasm of male germ cells. It is composed mainly of RNAs and RNA-binding proteins and is thus a type of RNP granule. Chromatoid body-like granules first appear in spermatocytes and condense into a single granule in round spermatids. The structure disappears again when spermatids start to elongate. The chromatoid body is crucial for spermatogenesis but its exact role in the process is not known. However, due to similarities with RNP granules found in somatic cells – such as stress granules and processing bodies – chromatoid body is thought to be involved in post-transcriptional regulation of gene expression. As chromatoid body is significantly bigger than other known RNP granules it is seen even with light microscopy and was discovered already in 1876 by A. von Brunn.