An NKX-COUP-TFII morphogenetic code directs mucosal endothelial addressin expression.

Area of Science:

• Vascular Biology
• Immunology
• Developmental Biology

Background:

• Vascular addressins, such as those encoded by Madcam1 and St6gal1, are critical for directing lymphocyte homing to intestinal tissues.
• These addressins are specifically expressed on endothelial cells in gut post-capillary and high endothelial venules (HEV), demonstrating organ- and segment-specific endothelial specialization.

Purpose of the Study:

• To identify the regulatory mechanisms controlling the organ- and segment-specific expression of mucosal vascular addressins.
• To elucidate the transcription factors and cis-regulatory elements involved in targeting addressin expression to specific endothelial cell populations.

Main Methods:

• Identification of conserved NKX-COUP-TFII composite elements (NCCE) in the regulatory regions of Madcam1 and St6gal1.
• Analysis of transcription factor binding to NCCE, including the homeodomain protein NKX2-3 and the nuclear receptor COUP-TFII.
• Functional studies involving overexpression of COUP-TFII and deficiency of NKX2-3 in endothelial cells.
• Investigation of Notch pathway signaling in regulating addressin expression.

Main Results:

• Conserved NCCE in Madcam1 and St6gal1 regulatory regions bind NKX2-3 and COUP-TFII cooperatively to activate transcription.
• The Madcam1 NCCE integrates repressive signals from arterial/capillary Notch effectors.
• Overexpression of COUP-TFII leads to ectopic addressin expression in NKX2-3+ capillaries.
• NKX2-3 deficiency abrogates addressin expression in HEV.
• Phylogenetically conserved NCCE are also found in genes related to neuron migration and organ morphogenesis.

Conclusions:

• The study defines an NKX-COUP-TFII morphogenetic code that dictates the expression of mucosal vascular addressins.
• This code provides a molecular basis for the targeted specialization of endothelial cells in the gut vasculature.
• The findings have implications for understanding immune cell trafficking and inflammatory processes in the intestine.