G. Mitta et al., Mussel defensins are synthesised and processed in granulocytes then released into the plasma after bacterial challenge, J CELL SCI, 112(23), 1999, pp. 4233-4242
MGD1 (Mytilus galloprovincialis defensin 1), a new member of the arthropod
defensin family, is a 4 kDa antibacterial peptide previously isolated from
the plasma of Mediterranean mussels, We report here the presence of MGD1 in
the organelle-rich fraction of hemocytes and the cDNA sequence correspondi
ng to MGD1 and one new isoform mRNA: MGD2, Sequence analysis indicated that
MGDs are synthesised as precursors consisting of a putative signal peptide
of 21 residues, the active peptide of 39 amino acids and a 21 residue carb
oxyl-terminal extension, rich in acidic amino acids. Localisation of the tr
anscripts by northern blot revealed that the precursors are abundantly expr
essed in hemocytes, Immunocytochemistry at both the optical and ultrastruct
ural levels showed that defensins (i) are predominantly located in vesicles
of a granulocyte subclass of hemocytes containing small granules, (ii) are
also found in large clear granules of another granulocyte subclass, and (i
ii) that MGD immune reactivity existed in granular structures of enterocyte
s, Finally, we revealed that bacterial challenge triggered a plasmatic incr
ease of MGD1 concentration and gave evidence of the simultaneous release of
the peptides from the hemocytes.