P38 participates in spermatogenesis and acrosome reaction prior to fertilization in Chinese mitten crab Eriocheir sinensis

• A novel non-tissue specific p38 protein kinase was characterized in Eriocheir sinensis.
• Total p38 protein increased, while phospho-p38 decreased, in testis development.
• Sperm morphological changes were observed during the acrosome reaction (AR).
• Localization of p38 in living sperm was detected during the AR.
• P38 may be involved in spermatogenesis and AR in E. sinensis.

P38 mitogen-activated protein kinases (MAPKs) comprise a family of serine/threonine protein kinases that play important roles in cellular responses to inflammatory cytokines and environmental stresses. These kinases are involved in controlling cell division, differentiation and death in mammalian testes and therefore are critical to spermatogenesis. To explore their functions in male reproduction of Chinese mitten crabs, Eriocheir sinensis p38 (Es-p38) protein expression was determined in different tissues including testes at different developmental stages by Western blot. Es-p38 was expressed in various tissues, with higher levels in the heart, stomach, gills and testes. Total Es-p38 protein levels increased gradually during spermatogenesis, but phosphorylated Es-p38 was much higher in the spermatid (August–October) than the spermatocyte (July–August) and sperm (October–January) stages. Trypan blue staining and hematoxylin/eosin staining were both used to detect sperm motility and changes in sperm morphology during the acrosome reaction (AR) induced by pre-incubation with A23187 in vitro, activated Es-p38 proteins detected by fluorescent microscopy were translocated gradually to nuclear and apical cap regions, accumulating at the anterior of the acrosomal tubule. The results suggest the involvement of p38 MAPK in spermatogenesis and the AR in E. sinensis.