The ancient role for GATA2/3 transcription factor homolog in the hemocyte production of oyster

Hemocytes, the cellular component of invertebrate hemolymph, are essential for invertebrate immunity, but the hematopoiesis and regulation mechanism are still largely unknown. In the present study, a conserved hematopoietic transcription factor Cg-GATA2/3 was identified in Pacific oyster Crassotrea gigas, which was evolutionarily close to the vertebrate GATA1/2/3. Cg-GATA2/3 was mainly distributed in the immune organs, such as gill, hemocytes, and mantle. After Cg-GATA2/3 was interferenced by dsRNA, the mRNA expressions of hemocytes specific gene (EcSOD) and hematopoietic transcription factor (C-Myb) were all significant down-regulated, and the hemocyte renewal rates also decreased both in hemolymph and gill. During the larval developmental stages, the mRNA transcripts of Cg-GATA2/3 increased immediately after fertilization and kept a high level during blastula and early trochophore larvae stage (4-10 hpf, hours post fertilization), then decreased sharply in early D-veliger larvae stage (15 hpf). Whole-mount immunofluorescence assay further revealed that the abundant immunoreactivity of Cg-GATA2/3 was distributed in the whole body of blastula and gastrula embryos, while specialized gradually to a ring structure around the dorsal region in trochophore larvae. In the D-veliger and umbo larvae, scattered positive signals appeared in the specific sinus structure on the dorsal side and velum region. These results demonstrated that Cg-GATA2/3 was a hematopoietic lineage-specific transcription factor to regulate the hemocyte production, and it could also be used as hematopoietic specific marker to trace potential developmental events of hematopoiesis during ontogenesis of oyster.