Distinct mechanisms control the timing of differentiation of two myeloid populations in Xenopus ventral blood islands

Previous study has suggested that distinct populations of myeloid cells exist in the anterior ventral blood islands (aVBI) and posterior ventral blood islands (pVBI) in Xenopus neurula embryo. However, details for differentiation programs of these two populations have not been elucidated. In the present study, we examined the role of Wnt, vascular endothelial growth factor (VEGF) and fibroblast growth factor signals in the regulation of myeloid cell differentiation in the dorsal marginal zone and ventral marginal zone explants that are the sources of myeloid cells in the aVBI and pVBI. We found that regulation of Wnt activity is essential for the differentiation of myeloid cells in the aVBI but is not required for the differentiation of myeloid cells in the pVBI. Endogenous activity of the VEGF signal is necessary for differentiation of myeloid cells in the pVBI but is not involved in the differentiation of myeloid cells in the aVBI. Overall results reveal that distinct mechanisms are involved in the myeloid, erythroid and endothelial cell differentiation in the aVBI and pVBI.