p57Kip2 regulates embryonic blood stem cells by controlling sympathoadrenal progenitor expansion

Abstract

Hematopoietic stem cells (HSCs) are of major clinical importance, and finding methods for their in vitro generation is a prime research focus. We demonstrate here that the cell cycle inhibitor p57Kip2/Cdkn1c limits the number of emerging HSCs by restricting the size of the sympathetic nervous system (SNS) and the amount of HSC-supportive catecholamines secreted by these cells. This regulation occurs at the SNS progenitor level and is in contrast to the cell-intrinsic function of p57Kip2 in maintaining adult HSCs, highlighting profound differences in cell cycle requirements of adult HSCs compared with their embryonic counterparts. Furthermore, this effect is specific to the aorta-gonads-mesonephros (AGM) region and shows that the AGM is the main contributor to early fetal liver colonization, as early fetal liver HSC numbers are equally affected. Using a range of antagonists in vivo, we demonstrate a requirement for intact b2-adrenergic signaling for SNS-dependent HSC expansion. To gain further molecular insights, we have generated a single-cell RNA-Seq dataset of all Ngfr+ sympathoadrenal cells around the dorsal aorta to dissect their differentiation pathway. Importantly, this not only defined the relevant p57Kip2-expressing SNS progenitor stage, but also revealed that some neural crest cells, upon arrival at the aorta, are able to take an alternative differentiation pathway, giving rise to a subset of ventrally restricted mesenchymal cells that express important HSC-supportive factors. Neural crest cells thus appear to contribute to the AGM HSC niche via two different mechanisms: SNS-mediated catecholamine secretion and HSC-supportive mesenchymal cell production.

Dissecting infant leukemia developmental origins with a hemogenic gastruloid model

“…2B) (Fig. 2C and S3C) which are not captured in the Fadlullah et al (2022) and the Vink et al (2020) studies, but have been reported to sustain HSC specification (Fitch et al, 2012; Kapeni et al, 2022). Both these niche cell types are specifically present at 192h (Fig.…”

“…Namely, we observed the successive specification of hemogenic endothelium (HE), and of pre-definitive erythro-myeloid progenitors (EMP), definitive myelo-lymphoid progenitors (MLP) and pre-HSC in coherent temporal progression, and we captured the formation of discrete micro-aggregates of hematopoietic cells in intimate association with endothelial-like lumina, reminiscent of mid-gestation HSC-generating aortic clusters. Hemato-endothelial development was accompanied by generation of stromal components critical for HSC emergence, including PDGFRA + mesenchyme (Chandrakanthan et al, 2022) and sympathetic neurons (Fitch et al, 2012; Kapeni et al, 2022), suggesting coordinated organisation of elements of a hemogenic niche. Importantly, the in vitro gastruloid system responded to a relevant oncogenic event unique to infant AML (infAML) and putatively characteristic of the developmental period, i.e.…”

Nupr1 Negatively Regulates Endothelial to Hematopoietic Transition in the Aorta‐Gonad‐Mesonephros Region

“…[21] Interestingly, other regulators, such as Dlk1 and p57Kip2, have also been reported to negatively regulate HSPC generation in a non-cell-autonomous manner. [22,23] Nevertheless, the molecular events and mechanisms restraining EHT are poorly understood.…”