A Novel Hemocyte-Derived Peptide and Its Possible Roles in Immune Response of Type A.

A wide variety of bioactive peptides have been identified in the central nervous system and several peripheral tissues in the ascidian type A (). However, hemocyte endocrine peptides have yet to be explored. Here, we report a novel 14-amino-acid peptide, CiEMa, that is predominant in the granular hemocytes and unilocular refractile granulocytes of . RNA-seq and qRT-PCR revealed the high expression in the adult pharynx and stomach. Immunohistochemistry further revealed the highly concentrated CiEMa in the hemolymph of the pharynx and epithelial cells of the stomach, suggesting biological roles in the immune response. Notably, bacterial lipopolysaccharide stimulation of isolated hemocytes for 1-4 h resulted in 1.9- to 2.4-fold increased CiEMa secretion. Furthermore, CiEMa-stimulated pharynx exhibited mRNA upregulation of the growth factor (), vanadium binding proteins ( and ), and forkhead and homeobox transcription factors (, , and ) but not antimicrobial peptides ( and ) or immune-related genes (, , and ). Collectively, these results suggest that CiEMa plays roles in signal transduction involving tissue development or repair in the immune response, rather than in the direct regulation of immune response genes. The present study identified a novel hemocyte peptide, CiEMa, which paves the way for research on the biological roles of hemocyte peptides in chordates.