Abstract: After meiosis, round spermatid develops into mature sperm through metamorphosis. During this stage, most cytoplasm in the germ cell is gradually lost. The histones associated with chromatin are replaced by transition proteins and eventually transformed into protamines. Thus, the spermatid chromatin is stringently packaged and highly concentrated. It was thought that the transcription activity of spermatid is lost and RNAs are absent in spermatid. Nevertheless, many types of transcripts are detected in recent years, including the transcripts needed during chromatin repackaged and some small RNAs, etc. Because histones in the nuclear are not replaced entirely, and there are some active sites on the chromatin, we conjectured that spermatid has some transcription activity, and this activity is regulated by hormone and epigenetic modification. These RNAs may be the residues in the spermatogenesis, or timely expressed during spermiogenesis. A deep study on gene transcription in spermiogenesis will help understand the genetic characteristics and provide the theoretic basis for reproductive control using male gamete. This article reviewed recent advances in spermiogenesis at gene transcription level and proposed the future research directions.

Key words: metamorphosis, spermiogenesis, protamine, gene transcription, transcriptional regulation