Project description:The vertebrate main-body axis is laid down during embryonic stages in an anterior-to-posterior (head-to-tail) direction, driven and supplied by posteriorly located progenitors. For the vertebral column, the process of axial progenitor cell expansion that drives axis elongation, and the process of segmentation which allocates these progenitors into repeating vertebral units, occurs seemingly uninterrupted from the first to the last vertebra. Nonetheless, there is clear developmental and evolutionary support for two discrete modules controlling processes within different axial regions: a trunk module and a tail module. The secreted signal Gdf11 has been identified as a principal regulator of timing the trunk-to-tail (T-to-T) transition, but has pleiotropic effects across much of the main body axis, highlighting the need to reveal intrinsic regulatory networks that function to exclusively control one or the other module. Here, we identify Nuclear receptor subfamily 6 group A member 1 (Nr6a1) as a master regulator of elongation, patterning and lineage allocation specifically within the trunk region of the mouse. Both gain- and loss-of-function in vivo analysis revealed that the precise level of Nr6a1 acts as a rheostat, expanding or contracting vertebral number of the trunk region autonomously from other axial regions. Moreover, the timely clearance of Nr6a1 observed at the T-to-T transition was essential in allowing the tail module to operate correctly. In parallel with these effects on vertebral number, we show that Nr6a1 controls the timely progression of global Hox signatures within axial progenitors, preventing the precocious expression of multiple posterior Hox genes as the trunk is being laid down and thus reinforcing that patterning and elongation are coordinated. Finally, our data supports a crucial role for Nr6a1 in regulating gene regulatory networks that guide cell lineage choice of axial progenitors between neural and mesodermal fate. Collectively, our data reveals an axially-restricted role for Nr6a1 in all major cellular and tissue-level events required for vertebral column formation, supporting the view that modulation of Nr6a1 expression level or function may underpin evolutionary changes in axial formulae that exclusively alter the trunk region.

Project description:CD47 is a transmembrane glycoprotein that is ubiquitously expressed in different organs and tissues (Barclay and Van den Berg 2014; Liu, et al. 2017). In the human immune system, CD47 interacts with some integrins, two counter-receptor signal regulator protein (SIRP) family members, and the secreted thrombospondin-1 (TSP1) (Barclay and Van den Berg 2014; Gao, et al. 2016; Kaur, et al. 2013; Oldenborg, et al. 2000). CD47 has two established roles in the immune system. The CD47-SIRPα interaction was identified as a critical innate immune checkpoint, which delivers an antiphagocytic signal to macrophages and inhibits neutrophil cytotoxicity (Martínez- Sanz, et al. 2021). Its interaction with inhibitory SIRPα is a physiological anti-phagocytic “don’t eat me” signal on circulating red blood cells that is co-opted by cancer cells (Matlung, et al. 2017). Many malignant cells overexpress CD47 (Betancur, et al. 2017; Chao, et al. 2011; Jaiswal, et al. 2009; Majeti, et al. 2009; Oronsky, et al. 2020; Petrova, et al. 2017). CD47/SIRPα-targeted therapeutics have been developed to overcome this immune checkpoint for cancer treatment (Kaur, et al. 2020; Matlung, et al. 2017). Secondly, engagement of CD47 on T cells by TSP1 regulates their differentiation and survival (Grimbert, et al. 2006; Lamy, et al. 2007) and inhibits T cell receptor signaling and antigen presentation by dendritic cells (DCs) (Kaur, et al. 2014; Li, et al. 2002; Liu, et al. 2015; Miller, et al. 2013; Soto-Pantoja, et al. 2014; Weng, et al. 2014). TSP1/CD47 signaling has similar inhibitory functions to limit NK cell activation (Kim, et al. 2008; Nath, et al. 2018; Nath, et al. 2019; Schwartz, et al. 2019) and IL1β production by macrophages (Stein, et al. 2016). CD47 is therefore a checkpoint that regulates both innate and adaptive immunity. The recent understanding of CD47 antagonism associated with increased antigen presentation by DCs (Liu, et al. 2016) and natural killer cell cytotoxicity (Nath, et al. 2019) contributes to the heightened interest in CD47 as a therapeutic target (Kaur, et al. 2020).

Dataset Information

Breaking constraint of mammalian axial formulae [ATAC-seq]

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