Plasmatocyte spreading peptide is encoded by an mRNA differentially expressed in tissues of the moth Pseudoplusia includens.

It has long been known that blood cells (hemocytes) are an essential component of the invertebrate immune system, yet little is known about the molecules mediating their function. Recently, we identified plasmatocyte spreading peptide (PSP1) from the moth Pseudoplusia includens which regulates the trafficking and adhesion of a hemocyte subclass called plasmatocytes. Here, we report the cloning of a cDNA (p15) that encodes a PSP1 precursor protein. Northern blot analysis revealed that a homologous prepro-PSP1 mRNA is expressed in fat body, and that other PSP1-related transcripts are expressed in nervous tissue and hemocytes. Coupled in vitro transcription/translation reactions indicated that p15 produces a protein recognized by a PSP1 polyclonal antibody. Immunoblotting experiments further revealed that a putative pro-PSP1 protein is present in P. includens plasma and fat body.