SG trNK cells emerge at 2–3 wk of age from cNK cells. (A–C) Representative flow cytometry plots (A), total cell count (B), and composition (C) of WT and Ncr1^CreTgfb1^fl SG group 1 ILCs at indicated age. (D)Id2^CreERTR26R^EYFP mice were treated once at P14 intraperitoneally (i.p.) with 1.5 mg of tamoxifen and analyzed at 2 or 5 mo of age. Scheme of tamoxifen administration and experimental setup (left), percentage of EYFP⁺ SG trNK cells (right). mo, months. wks, weeks. (E–J) Single-cell transcriptomes of group 1 ILCs from 3-wk-old SGs, generated using 10X Genomics. (E) UMAP with clusters identified based on ILC1 or cNK cell signature gene expression. (F) Heatmap showing expression of marker genes for each cluster depicted in E. (G) Analysis of regulatory network activity using SCENIC (Aibar et al., 2017). (H) Trajectory inference of group 1 ILCs from all time points using RNAVelocity (Bergen et al., 2020). Ratios of spliced and unspliced mRNAs reveal trajectory toward trNK cluster. (I) Color-coded TGF-β pathway activity quantified with PROGENy (Schubert et al., 2018). (J) Color-coded expression of indicated genes. (K) Expression of integrin α-V on indicated cell populations, measured by flow cytometry. Spl, spleen. (A–D and K) Data from two to three independent experiments with total n = 5–7 mice per timepoint and group. Error bars display means ± SD. Statistical significance was calculated using one-way ANOVA or two-tailed t test; ****P < 0.0001. ns, not significant.