Hapln1b, a central organizer of the ECM, modulates kit signaling to control developmental hematopoiesis in zebrafish

Abstract

During early vertebrate development, hematopoietic stem and progenitor cells (HSPCs) are produced from hemogenic endothelium located in the dorsal aorta, before they migrate to a transient niche where they expand, the fetal liver and the caudal hematopoietic tissue (CHT), in mammals and zebrafish, respectively. In zebrafish, previous studies have shown that the extracellular matrix (ECM) around the aorta needs to be degraded to allow HSPCs to leave the aortic floor and reach blood circulation. However, the role of the ECM components in HSPC specification has never been addressed. We show here that hapln1b, a key component of the ECM is specifically expressed in hematopoietic sites in the zebrafish embryo. Gain- and loss-of-function experiments all resulted in the absence of HSPCs in the early embryo, showing that hapln1b is required, at the correct level, to specify HSPCs in the hemogenic endothelium. Furthermore, we show that the expression of hapln1b is necessary to maintain the integrity of the ECM through its link domain. By combining functional analyses and computer modelling, we show that kitlgb interacts with the ECM to specify HSPCs. We demonstrate that the ECM is an integral component of the microenvironment and mediates cytokine signalling that is required for HSPC specification.

Expression of Nerve Growth Factor and Its Receptor TrkA in the Reproductive System of Adult Zebrafish

“…Digoxigenin (DIG)-labeled antisense riboprobes, were prepared as reported in previous studies [ 49 , 50 , 51 ]. In detail, ngf and trka expressions were detected using in situ hybridization (ISH).…”

Synergistic prostaglandin E synthesis by myeloid and endothelial cells promotes fetal hematopoietic stem cell expansion in vertebrates

“…To generate digoxigenin and fluorescein‐labeled probes cmyb , runx1 , pu1 , gata1 , flk1 , and rag1 were previously described (Cacialli et al , 2019 ; Cacialli et al , 2021 ; Mahony et al , 2021 ). Whole‐mount in situ hybridization (WISH) was performed on 4% paraformaldehyde‐fixed embryos.…”

“…The use of vertebrate model organisms such as mouse and zebrafish has contributed to clarify the mechanisms of hematopoietic development. HSCs first arise from hemogenic endothelium in the dorsal aorta (Bertrand et al , 2010 ; Mahony et al , 2021 ). Through blood circulation, they colonize a transient hematopoietic niche before they settle in the adult marrow.…”

Analysis of the Expression of Neurotrophins and Their Receptors in Adult Zebrafish Kidney

“…The renal interstitium of the zebrafish contains hematopoietic cells [47][48][49][50][51]; thus, it could be considered equivalent to the bone marrow in mammals [52][53][54]. During development, the hematopoietic stem progenitor cells (HSPCs) emerge from the dorsal aorta, colonize the caudal hematopoietic tissue (equivalent to the mammalian fetal liver), and migrate to the kidney marrow [55,56].…”