RET is functionally active in CD34⁺CD38^– HSPCs, and cell surface expression enriches for HSC function. (A) Kinase activity alterations between CD34⁺CD38^– HSPCs (green) and CD34⁺CD38⁺ HPCs (lilac). (B) Process network enrichment for significantly altered kinases and phosphorylation events from panel A. (C) z-normalized geometric mean fluorescence intensity of cell surface RET within the indicated populations. Significance was tested by using a paired Student t test for individual cord blood donors tested (N = 9). (D) Plot depicting frequencies and confidence interval for RET^hi (red) and RET^low (blue) CD34⁺CD38^– cell in vivo engraftment at limiting dilution after 12 weeks (N = 3 mice per dose tested). (E) Table of 1/stem cell frequency numerical data calculated from the in vivo limiting dilution analysis presented in panel D, including: estimated stem cell frequency, upper and lower intervals of estimation, χ² test, and estimated P value.