The Seasonal and Stage-Specific Expression Patterns of HMGB2 Suggest Its Key Role in Spermatogenesis in the Chinese Soft-Shelled Turtle (Pelodiscus sinensis).

HMGB2, a member of the high-mobility group (HMG) proteins, was identified as a male-biased gene and plays a crucial role in the germ cells differentiation of mammals. However, its role in spermatogenesis of turtle is still poorly understood. Here, we cloned the Pelodiscus sinensis HMGB2 and analyzed its expression profile in different tissues and in testis at different developmental ages. P. sinensis HMGB2 mRNA was highly expressed in the testis of 3-year-old turtles (P < 0.01), but was hardly detected in ovaries and other somatic tissues. The results of chemical in situ hybridization (CISH) showed that HMGB2 mRNA was specifically expressed in germ cells, where it was mainly distributed in round spermatids and sperm, but not detected in somatic cells, spermatogonia, primary spermatocytes, or secondary spermatocyte. The relative expression of HMGB2 also responded to seasonal changes in testis development in P. sinensis. In different seasons of the year, the relative expression of HMGB2 transcripts in the testis of 1 year and 2 year olds showed an overall upward trend, whereas, in the testis of 3 year old, it peaked in July and then declined in October. Moreover, in April and July, with an increase in ages, the expression of HMGB2 transcripts showed an upward trend. However, in January and October, there was a decline in expression in testis in 3-year-old turtles. These results showed that HMGB2 is closely related to spermatogenesis in P. sinensis.