Homogenic endothelium-independent hematopoiesis ensures the abundance of erythrocytes and macrophages during zebrafish development.

Abstract

In all organisms studied, from flies to humans, blood cells emerge in several sequential waves and from distinct hematopoietic origins. However, the relative contribution of these ontogenetically distinct hematopoietic waves to embryonic blood lineages and to tissue regeneration during development is yet elusive. Here, using a lineage-specific switch and trace strategy in the zebrafish embryo, we report that the definitive hematopoietic progeny barely contributes to erythrocytes and macrophages during early development. Lineage tracing further show that ontogenetically distinct macrophages exhibit differential recruitment to the site of injury based on the developmental stage of the organism. We further demonstrate that primitive macrophages can solely maintain tissue regeneration during early larval developmental stages after selective ablation of definitive macrophages. Our findings highlight that the sequential emergence of hematopoietic waves in embryos ensures the abundance of blood cells required for tissue homeostasis and integrity during development.

A non-invasive photoactivatable split-Cre recombinase system for genome engineering in zebrafish

“…In addition, we tested the functionality of the PA-Cre system under the kdrl promoter 32,33 , which exhibits expression during gastrulation, in the lateral plate mesoderm, and in endothelial cells [33][34][35] . To examine the potential of the kdrl-PA-Cre system for erythrocyte labeling, we injected a kdrl-PA-Cre construct into Tg(α/βa2-globin:loxP-DsRedx-loxP-GFP) embryos at one-cell stage, as erythrocytes are known to be derived from the lateral plate mesoderm [36][37][38][39] . Following blue light illumination from 6 hpf to 18 hpf in injected embryos, GFP expression was observed in erythrocytes at 24 hpf, indicating successful Cre/loxP recombination.…”