The role of phospholipase C gamma 1 in primitive hematopoiesis during zebrafish development

Objectives: Phospholipase C (PLC) gamma 1 has been shown to mediate signal transduction of tyrosine kinases and affect function of hematopoietic cells. However, its role in hematopoiesis during embryonic development is currently unclear. In this study, we examined this issue using morpholino (MO) gene knockdown in zebrafish embryos. Methods: MO targeting at the exon-1-intron-1 junction of zebrafish PLC-γ1 was injected into embryos at the one- to four-cell stage (referred herein zPLC-γ1MOembryos). Primitive hematopoiesis was examined quantitatively by flow cytometry in Tg(gata1:GFP) embryos and by real-time quantitative polymerase chain reaction at 18 hours-post-fertilization (hpf), before the onset of circulation. The embryos were also treated with receptor inhibitors of vascular endothelial growth factor, fibroblast growth factor, and platelet-derived growth factor at 25, 1, and 30 μmol/L, respectively, from one cell until 48 hpf. Results: Erythropoiesis was reduced in zPLC-γ1MOembryos, as shown by the reduction in gata1+cells (wild-type: 4.32% ± 0.10% vs zPLC-γ1MO: 2.38% ± 0.11%, p = 0.021) and gata1 and α-embryonic hemoglobin expression [0.47 ± 0.06-fold (p = 0.013) and 0.46 ± 0.04-fold (p = 0.013)]. Expression of scl, lmo-2 (early hematopoietic progenitors), pu.1, and l-plastin (myelomonocytic lineages) as well as fli1 (vascular progenitors) were unaffected. Fli1+cells in Tg(fli1:GFP) embryos were also unaffected by zPLC-γ1MO. When embryos were incubated with receptor inhibitors of vascular endothelial growth factor (VEGFRTKI), fibroblast growth factor (SU5402), or platelet-derived growth factor (AG1296), only VEGFRTKI reduced erythropoiesis [VEGFRTKI: 2.10% ± 0.07% (p = 0.021) vs SU5402: 4.08% ± 0.12% (p = 0.248) vs AG1296: 4.12% ± 0.14% (p = 0.149)]. Conclusion: PLC-γ1 is involved in the regulation of primitive hematopoiesis in zebrafish embryos, which is distinct from its later effect on vascular formation.