β-defensin is a kind of important antimicrobial peptides in innate immune system which plays significant role in the defense of pathogenic microbial infection.

The Research Group of Fish Developmental Genetics and Cell Engineering at Institute of Hydrobiology, Chinese Academy of Sciences (IHB), led by Prof. GUI Jianfang, recently cloned and characterized a β-defensin from pituitary cDNA library of a protogynous hermaphroditic orange-spotted grouper (Epinephelus coioides).

The β-defensin was shown to be dominantly expressed in pituitary and testis by RT-PCR and Western blot analysis, and its transcript level is significantly upregulated in reproduction organs from intersexual gonad to testis during the natural and artificial sex reversal. Promoter sequence and the responsible activity region analyses revealed the pituitary-specific POU1F1a transcription binding site and testis-specific SRY responsible site.

Moreover, both in vitro antibacterial activity assay of the recombinant β-defensin and in vivo embryo microinjection of the β-defensin mRNA were shown to be effective in killing Gram-negative bacteria. The antibacterial activity was sensitive to concentrations of Na⁺, K⁺, Ca²⁺ and Mg ²⁺.

The findings strongly suggest that the fish β-defensin might play significant roles in both innate immunity defense and reproduction endocrine regulation and might open the door for understanding the reproduction and endocrine regulation roles of β-defensin in fish.   

This work was funded by National Key Basic Research Program, National Natural Science Foundation of China etc. It was completed by IHB doctoral student JIN Junyan et al. The paper was published online in PLoS ONE. 

http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0012883