PMC

Overview of zebrafish developmental myelopoiesis, key transgenic lines, and lineage identification tools labelling myeloid cell populations during developmental haematopoiesis. (Transgenic lines are shown in green, other specific lineage identifiers are in blue.) PM: primitive myelopoiesis; EMP: erythromyeloid progenitors; HSPCs: haematopoietic stem and progenitor cells; CMP: common myeloid progenitor; CLP: common lymphoid progenitor; MEP: megakaryocyte/erythroid progenitor; GMP: granulocyte/monocyte progenitor; PHA: peanut haemaglutinin. **Denotes lineages only demonstrated in adult zebrafish. Lineage intermediates are shown for clarity but are yet to be isolated as distinct populations in zebrafish.

Origin and development of dendritic cells. With the exception of LCs, DCs develop from bone marrow-derived precursors. CDPs give rise to cDCs and pDCs. Monocytes differentiate into MoDCs in tissue as a consequence of inflammation or infection. LCs originate in prenatal precursor cells and are maintained locally by self-renewal under steady-state conditions. While under a severe inflammatory condition, LCs are replaced by blood-borne monocytes and acquire the capacity of self-renewal. DC, dendritic cell; LC, langerhans cells; CDP, common dendritic cell progenitor; cDC, classical dendritic cell; pDC, plasmacytoid dendritic cell; MoDC, monocyte-derived dendritic cell; YS-EMPs, Yolk sac-derived erythromyeloid progenitor cells; P-Sp/AGM para-aortic splanchnopleure/aorta, gonads, and mesonephros; HSC, hematopoietic stem cells; CMP, common myeloid progenitor cell; MP, myeloid progenitor cell; cMoP, common monocyte progenitor; GMP, granulocyte-macrophage progenitor; MDP, monocyte-macrophage DC progenitor.

(A) The decrease in HSC numbers after Zfx deletion from the BM. Shown are absolute numbers of total BM cells, myeloid progenitors and the HSC-containing LSK population in control and Mx1-Cre⁺ Zfx^flox/y CKO mice two weeks after pI·C injection. Each symbol represents an individual mouse. (B) The loss of HSC from the stem/progenitor compartment of Mx1-Cre⁺ CKO BM at the indicated times after pI·C injection. Shown are the staining profiles of Lin⁻ cells, with the LSK population (red) and erythromyeloid progenitors (blue) and their percentages indicated (average ± S.D. of 3–12 animals). The graph shows average ratios of the LSK to myeloid progenitor fractions. (C) The loss of adult HSC after constitutive Zfx deletion in the hematopoietic system. The HSC and myeloid progenitor populations in the fetal liver (n=6–9) or in adult BM (n=4–5) of Tie2-Cre⁺ CKO and control mice are shown as in panel B. (D) Decreased HSC and lymphoid progenitors but normal myeloid progenitors in Mx1-Cre⁺ CKO mice two weeks after pI·C injection. Shown are Flt3⁻ and Flt3⁺ LSK populations containing long-term and short-term HSC, respectively; Flt3⁺ Lin⁻ c-Kit^low lymphoid progenitors including the IL-7Rα₊ CLP subset (red); and Lin⁻ Sca-1⁻ c-Kit⁺ erythromyeloid progenitors divided into common myeloid progenitor (red), erythrocyte/megakaryocyte progenitor (blue) and granulocyte/monocyte progenitor (green). The fraction of each subset in the Lin⁻population is indicated (average ± S.D. of 5 animals). (E) Increased HSC apoptosis in Mx1-Cre⁺ CKO mice two weeks after pI·C injection. Shown are gated HSC (the LSK subset) and erythromyeloid progenitors (Lin⁻ Sca-1⁻ c-Kit⁺) stained for Annexin V and DNA content (7-AAD). The fractions of Annexin⁺ 7-AAD^- apoptotic cells (highlighted) are indicated (average ± S.D. of 3 animals). (F) Normal erythromyeloid progenitor function in Zfx-deficient BM. Shown is in vitro colony formation by BM cells from Mx1-Cre⁺ CKO or control mice two weeks after pI·C injection (average ± S.D. of 4 animals).

(A) Composite May-Grünwald Giemsa images of hematopoietic cells isolated from the lymphoid fraction in (1000x, scale bar is 10 μm). (B) Composite May-Grünwald Giemsa images of hematopoietic cells isolated from the precursor fraction in (1000x, scale bar is 10 μm). (C) RT-PCR of leukocyte- (cd45), progenitor- (cmyb), erythromyeloid- (cd41, mpx, band3, and gata1), B cell- (pax5 and igm), and T cell- (lck) specific transcripts isolated from the cultures as in A and B. Gel images have been cropped for clarity of presentation.