Sustained postnatal LIN28B expression limits inflammation-induced Mk lineage output. (A) CD41⁺ frequency in phenotypic HSCs from 8-week-old tet-Lin28b and littermate (ctrl) mice induced with DOX from birth. Mice were either kept unperturbed or treated with 10 μg/g pIpC and analyzed by using FACS 16 hours later. Statistical significance determined by multiple t tests using the Holm-Šídák method. n = 3 to 8. (B) Representative FACS histograms showing CD41⁺ HSC frequency in pIpC-treated mice. (C) Relative platelet frequency in peripheral blood from tet-Lin28b and ctrl mice after pIpC treatment measured by FACS. Statistical significance for each time point was determined by multiple t tests assuming equal standard deviation. Day 5, P = .003; day 8, P = .002. (D) Experimental outline for repetitive postnatal pIpC treatments of juvenile mice. Three consecutive weekly treatments of intraperitoneal injection of 10 μg/g pIpC started in 10-day-old (d10) wild-type (WT) pups followed by end point analysis between 7 and 9 weeks of age. (E) FACS analysis of CD41⁺ HSC frequency (left) in WT mice after repetitive pIpC or PBS injections and (right) tet-Lin28b and ctrl mice after repetitive pIpC treatment (n = 7-9). P values were determined by using the Mann-Whitney test. (F) Representative FACS histograms of CD41⁺ HSCs from repetitive pIpC-treated tet-Lin28b and control mice. (G) FACS analysis of CD41⁺ frequency in HSCs from 8-week-old mice of the indicated genotypes treated with the repetitive postnatal pIpC regimen. P value was determined by using the Mann-Whitney test. (H) LIN28B-eGFP reporter mouse model design and FACS histograms showing decreasing LIN28B protein levels across developmental time. (I) Compiled frequency of eGFP⁺ HSCs at the indicated ages. eGFP⁺ gating is based on WT littermate controls (n = 2-7 per time point). (J) FACS analysis of eGFP⁺ levels and frequency in HSCs from 11-day-old (d11) mice 16 hours after 10 μg/g pIpC challenge. ∗P < .05. P value was determined by using the Mann-Whitney test. 3′UTR, 3′ untranslated region; LSK, lineage^–Sca1⁺cKit⁺.