A DEAB-sensitive aldehyde dehydrogenase regulates hematopoietic stem and progenitor cells development during primitive hematopoiesis in zebrafish embryos.

Although aldehyde dehydrogenase (ALDH) activity has become a surrogate of hematopoietic stem and progenitor cells (HSPCs), its function during hematopoiesis was unclear. Here, we examined its role in zebrafish hematopoiesis based on pharmacological inhibition and morpholino (MO) knockdown. Zebrafish embryos were treated with diethylaminobenzaldehyde (DEAB, 1 µmol/l) between 0- and 48 hour-post-fertilization (hpf). MOs targeting aldhs were injected between 1 and 4-cell stage. The effects on hematopoiesis were evaluated at different stages. DEAB treatment between 0 and 18 hpf increased gene expression associated with HSPC (scl, lmo2), erythropoiesis (gata1, α- and ß-eHb) and myelopoiesis (spi1) as well as gfp(+) cells in dissociated Tg(gata1:gfp) embryos. The effects were ameliorated by all-trans retinoic acid (1 nmol/l). Definitive hematopoiesis and the erythromyeloid precursors were unaffected. In all, 14 out of 15 zebrafish aldhs were detectable by reverse transcription PCR in 18 hpf embryos, of which only aldh1a2 and aldh16a1 were expressed in sites pertinent to hematopoiesis. Molecular targeting by MOs was demonstrated for 15 aldhs, but none of them, even in combined aldh1a2 and aldh1a3 knockdown, recapitulated the hematopoietic expansion in DEAB-treated embryos. In conclusion, DEAB expands HSPC population during primitive hematopoiesis through inhibition of aldh and retinoic acid synthesis. The specific aldh isoform(s) remains to be determined.

The role of survivin2 in primitive hematopoiesis during zebrafish development.

Survivin is an inhibitor of apoptosis and its role in embryonic development is not completely understood. In zebrafish, survivin undergoes gene duplication. Survivin1 (sur1) has been shown to mediate angiogenesis but not hematopoiesis. In this study, we examined survivin2 (sur2) with particular reference to its role in primitive hematopoiesis during zebrafish development. sur2 was expressed predominantly in the intermediate cell mass (ICM, site of primitive hematopoiesis). Morpholino (MO) targeting at intron1-exon2 junction of sur2 significantly reduced green fluorescent protein(+) (erythroid) cell population in transgenic Tg (gata1:gfp) embryos at 18 h post-fertilization (h.p.f.; wild type: 4.49+/-0.15%; Sur2(MO) embryos: 2.22+/-0.12%, P=0.02). Molecular targeting was confirmed by reverse transcription-PCR and MO specificity by successful sur2 mRNA rescue. sur2 MO also downregulated genes associated with hematopoietic stem cells (scl, lmo2), erythroid (gata1, alpha- and beta-embryonic hemoglobins) as well as early (pu.1) and late (mpo, l-plastin) myelomonocytic lineages at 12 and 18 h.p.f. This was associated with an increase in apoptosis in the ICM and alteration of cell-cycle status of erythroid cells. Both effects were caspase dependent. In conclusion, sur2 is important in maintaining hematopoietic stem and lineage committed cells during zebrafish development, by virtue of its antiapoptotic activity in a caspase dependent and cell autonomous fashion.