Myeloid cells, composed of granulocytes and monocytes, have very significant roles in the immune response and tissue remodeling. All myeloid cells are derived from hematopoiesis. Similar to mammals, zebrafish hematopoiesis consists of two waves, primitive hematopoiesis and definitive hematopoiesis. These two waves take place in different locations at different time course. Primitive hematopoiesis is a transient wave and takes place in the early stage. It mainly gives rise to myeloid cells and erythrocytes. Definitive hematopoiesis can generate hematopoietic stem cells, which can give rise to all kinds of cells of blood lineage including myeloid cells, erythrocytes and lymphocytes. The macrophages generated by hematopoiesis will migrate into different organs to become tissue resi...[ Read more ]

Myeloid cells, composed of granulocytes and monocytes, have very significant roles in the immune response and tissue remodeling. All myeloid cells are derived from hematopoiesis. Similar to mammals, zebrafish hematopoiesis consists of two waves, primitive hematopoiesis and definitive hematopoiesis. These two waves take place in different locations at different time course. Primitive hematopoiesis is a transient wave and takes place in the early stage. It mainly gives rise to myeloid cells and erythrocytes. Definitive hematopoiesis can generate hematopoietic stem cells, which can give rise to all kinds of cells of blood lineage including myeloid cells, erythrocytes and lymphocytes. The macrophages generated by hematopoiesis will migrate into different organs to become tissue resident macrophages, such as microglia in the brain.

The origin of tissue resident macrophages is an interesting research field to investigate. Myeloid cell fate mapping in mice has been conducted by many groups to figure out which hematopoietic wave tissue resident macrophages are derived from. However, there has not been a consensus in this issue yet, and it still remains an open question. We tried to label different waves of myeloid cells in zebrafish embryos and observe their distribution in the adult organs. Two transgenic lines Tg(coro1a:CreER ^T2) and Tg(coro1a:LOXP-DsRedx-LOXP-eGFP) were generated, and this Cre-lopx system can permanently convert Dsred positive myeloid cells into GFP positive myeloid cells. Taking the advantage of model system zebrafish, we can label one wave of myeloid cells with different methods. Preliminary data show that controlling the time of labelling using Tg(coro1a:CreER ^T2) line or controlling the location of labelling using (hsp70:mCherry-T2a-CreER^T2) ^#12 line with a local IR laser induction may effectively label myeloid cells at different time course or in different locations. Therefore, it is shown this system can be applied in the myeloid cell fate mapping experiment in zebrafish.