Abstract

CXC-chemokine receptor type 4 (CXCR4), a 7-transmembrane receptor family member, displays multifaceted roles, participating in immune cell migration, angiogenesis, and even adipocyte metabolism. However, the activity of such a ubiquitously expressed receptor in epithelial gland organogenesis has not yet been fully explored. To investigate the relationship between CXCL12/CXCR4 signaling and embryonic glandular organogenesis, we used an ex vivo culture system with live imaging and RNA sequencing to elucidate the transcriptome and protein-level signatures of AMD3100, a potent abrogating reagent of the CXCR4-CXCL12 axis, imprinted on the developing organs. Immunostaining results showed that CXCR4 was highly expressed in embryonic submandibular gland, lung, and pancreas, especially at the periphery of end buds containing numerous embryonic stem/progenitor cells. Despite no significant increase in apoptosis, AMD3100-treated epithelial organs showed a retarded growth with significantly slower branching and expansion. Further analyses with submandibular glands revealed that such responses resulted from the AMD3100-induced precocious differentiation of embryonic epithelial cells, losing mitotic activity. RNA sequencing analysis revealed that inhibition of CXCR4 significantly down-regulated polycomb repressive complex (PRC) components, known as regulators of DNA methylation. Treatment with PRC inhibitor recapitulated the AMD3100-induced precocious differentiation. Our results indicate that the epigenetic modulation by the PRC-CXCR12/CXCR4 signaling axis is crucial for the spatiotemporal regulation of proliferation and differentiation of embryonic epithelial cells during embryonic glandular organogenesis.

Highlights

  • CXC-chemokine receptor type 4 (CXCR4) and its ligand, CXCL12 or SDF-1, have been investigated largely in immunology and found fame for their critical function in systemic homeostasis as the major cell migration-regulating axis [1]

  • To determine the spatiotemporal dynamics of CXCR4 and CXCL12 expression during murine embryonic submandibular gland (eSMG) branching morphogenesis, we adopted and followed an ex vivo culture method established by Knox et al [27] (Figure 1A)

  • Cxcr4 and Cxcl12 expression gradually decreased from E13 to E17, and a reciprocal temporal expression pattern was detected for keratin 15 (Krt15), an epithelial stem cell marker (Figure 1C)

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Summary

Introduction

CXC-chemokine receptor type 4 (CXCR4) and its ligand, CXCL12 or SDF-1, have been investigated largely in immunology and found fame for their critical function in systemic homeostasis as the major cell migration-regulating axis [1]. A recent study showed that the CXCR4-CXCL12 axis governs metabolism pathways where CXCL12 activated brown adipose tissue to stabilize metabolic homeostasis in mice [3]. Such flexibility is largely contributed by the stimulation of diverse G-protein-dependent and -independent pathways and the notable expression mechanism of CXCR4 characterized by agile endocytosis and recycling patterns. The cellular CXCR4 proteins, which are predominantly localized in intracellular cytoplasm, are partially-to-mostly expressed at the surface membrane upon stimulation by CXCL12 [4]

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