Speaker: Kayla Bayless, Texas A&M University School of Medicine associate professor in cell biology and genetics

Title: "Transcriptomic analyses reveal new markers of angiogenic sprout initiation"

Abstract: The Bayless laboratory is interested in how new blood vessels form. During new blood vessel growth, endothelial cells change dramatically from quiescent cells that form the inner lining of the vascular system and acquire an invasive phenotype. Transcriptional changes are vital for this switch, but a comprehensive genome-wide approach focused exclusively on endothelial cell sprout initiation has not been reported. We developed a method to physically separate invading and non-invading cells initiating the process of new blood vessel formation and then used transcriptomics to analyze multiple independent biological replicates using single-cell RNA sequencing, bulk RNA-sequencing, and single cell cluster analysis of both invading and non-invading populations. We observed a gene signature in invading cells that contained numerous AP-1 transcription factors and was largely congruent with independent verification studies using qPCR; 16 candidate genes that were commonly upregulated in invading cells in the three transcriptomic analyses performed. Many of these have been linked to regulation of either epithelial- or endothelial-mesenchymal transition (EMT/ EndMT), implying rapid change in phenotype. Silencing SNAI1, a known regulator of EndMT, partially reduced invasion. Blocking AP-1 transcription factor activity and silencing JunB reduced SNAI1 expression, invasion distance and expression of genes controlling EndMT and EMT within hours of initiating invasion. These data show that partial EndMT initiated by the AP-1 transcription factor JunB occurs rapidly at the onset of angiogenesis to drive invasion. The gene signature in the non-invading population was consistent with activation of proliferation. FUCCI reporter and Edu staining indicated that non-invading cells enter S-phase at a higher rate than invading cells, indicating that the invading population is in a differentiated state expressing EndMT markers. Altogether, these studies expand genetic markers for partial EndMT, more clearly define transcriptional changes that control early endothelial cell sprout initiation and illuminate molecular changes that coordinate endothelial cell assembly into new vessels.

Host: Jeff Essner, genetics, development and cell biology professor