Fig 1: Pseudotime analysis of nonsmoker secretory cell differentiation.a Assessment of epithelial cell differentiation using Slingshot pseudotime value. Shown are epithelial cells differentiating in the secretory pathway including basal cells (BC, pink), intermediate cells (IC, orange), the progenitor club cell cluster (CC1, red), the effector club cell cluster (CC3, yellow), the proliferating club cell cluster (CC2, blue) and mucous cells (MC, green) for nonsmokers (NS) and smokers (S) plotted separately. Superimposed on each tSNE plot, the Slingshot pseudotime analysis shows the path of differentiation assuming basal cells as a starting point. b Pseudotime analysis. The extent of differentiation from the starting point was evaluated using a pseudotime analysis separately for nonsmokers (NS) and smokers (S). The results for each cluster have been plotted to enable pairwise comparisons. Significance of differences in the differentiation of each cluster is indicated by the p value to the right of the graph. p values were determined using a t test applied to the pseudotime values extracted by Slingshot. c Stem-progenitor activity of CC1 correlates with elevated KRT5 expression. Expression levels measured by the number of unique molecular identifiers (UMI) detected per cell during single cell RNA sequencing were plotted for KRT5 and KRT7 as a function of cluster for NS and S. Significant differences between NS and S are indicated by p values. Note that KRT5 levels in CC1 in NS have a mean that is greater than KRT5 expression in IC. KRT5 levels are considered a marker of stem-progenitor cells and are commonly thought to steadily fall as differentiation proceeds (see Supplementary Fig. 3). Expression of high levels of KRT5 in CC1 support CC1 as a branch point in the trajectory. At the same time, KRT7, a marker of club cells (see Supplementary Fig. 3), is clearly elevated in CC1 confirming the identity of CC1 as club cells rather than basal cells. d Change in branch point in smokers correlates with elevated SPDEF activity. Significant changes in expression levels of genes known to be up- or down-regulated by SPDEF were assessed in CC1 and CC3. Up-regulated genes included CEACAM5 and GCNT3. Down-regulated genes included SCGB1A1, SCGB3A1, LTF, and AQP5. Note that AQP5 is also up-regulated by oxidant stress such as exposure to cigarette smoke, potentially explaining the lack of down-regulation by smoking in CC1 and CC3. Significance of difference for panels c and d was determined based on the combined conditions of an adjusted p value < 0.05 (Bonferroni corrected) and a log fold change > 0.25. Violin plots in panels b–d include box-and-whisker plots showing the mean, 2nd and 3rd quartiles (box), range from minimum to maximum (whiskers), and outliers (dots).