Identification of transcripts expressed preferentially in hemocytes of Ciona intestinalis that can be used as molecular markers

The immunity provide by ascidian hemocytes represents one prototype of innate immune function in vertebrates. However, there are currently no molecular markers of ascidian hemocytes. We accumulated a large number of ESTs of cDNAs derived from hemocytes of Ciona intestinalis, a cosmopolitan species of ascidian. By comparing these ESTs with those derived from other tissues and developmental stages of Ciona, we were able to extract 81 transcripts expressed abundantly and preferentially in hemocytes. Among them, the von Willebrand factor type A (vWA)-like and complement 6 (C6)-like transcripts were found to be expressed almost exclusively in hemocytes, based on RT-PCR analysis and whole mount in situ hybridization. We propose that vWA-like and C6-like can be used as molecular markers for Ciona hemocytes.