Conserved hemopoietic transcription factor Cg-SCL delineates hematopoiesis of Pacific oyster Crassostrea gigas

• Cg-SCL was evolutionarily close to the orthologs in deuterostomes.
• Cg-SCL was highly distributed in the hemocytes as well as gill and mantle tissue.
• Knock down of Cg-SCL led to the down-regulation of hemocyte related genes.
• The immunoreactivity of Cg-SCL appeared in blastula larvae and maintained until D-veliger larvae.
• Available hematopoietic regulation occurred in oyster larvae.

Hemocytes are the effective immunocytes in bivalves, which have been reported to be derived from stem-like cells in gill epithelium of oyster. In the present work, a conserved haematopoietic transcription factor Tal-1/Scl (Stem Cell Leukemia) was identified in Pacific oyster (Cg-SCL), and it was evolutionarily close to the orthologs in deuterostomes. Cg-SCL was highly distributed in the hemocytes as well as gill and mantle. The hemocyte specific genes Integrin, EcSOD and haematopoietic transcription factors GATA3, C-Myb, c-kit, were down-regulated when Cg-SCL was interfered by dsRNA. During the larval developmental stages, the mRNA transcripts of Cg-SCL gradually increased after fertilization and peaked at early trochophore larvae stage (10 hpf, hours post fertilization), then sharply decreased in late trochophore larvae stage (15 hpf) before resuming in umbo larvae (120 hpf). Whole-mount immunofluorescence assay further revealed that the immunoreactivity of Cg-SCL appeared in blastula larvae with two approximate symmetric spots, and this expression pattern lasted in gastrula larvae. By trochophore, the immunoreactivity formed a ring around the dorsal region and then separated into two remarkable spots at the dorsal side in D-veliger larvae. After bacterial challenge, the mRNA expression levels of Cg-SCL were significantly up-regulated in the D-veliger and umbo larvae, indicating the available hematopoietic regulation in oyster larvae. These results demonstrated that Cg-SCL could be used as haematopoietic specific marker to trace potential developmental events of hematopoiesis during ontogenesis of oyster, which occurred early in blastula stage and maintained until D-veliger larvae.