Loss of Morrbid rescues mature and immature myeloid cells in the BM and spleen of Shp2* mice. Mononuclear cells were collected from the BM (A-C) and spleens (D-E) of the 4 experimental groups (WT, Shp2*, M, and Shp2*M; age, 3-4 months) for analyzing hematopoiesis. Changes in myeloid progenitors, GMPs, and mature myeloid cells were analyzed. Lin⁻Sca1⁻cKit⁺ cells were pregated for GMP flow cytometry profiles (CD34⁺CD16⁺). In BM, both the frequency and number of GMPs and mature myeloid cells were quantified. In spleen, only the frequency of GMPs and mature myeloid cells was quantified. (F) The level of apoptosis in mature myeloid cells was determined by flow cytometry using annexin-V staining, a marker for proapoptosis. (G) The level of Bim expression in mature myeloid cells was determined by intracellular flow cytometry with an anti-Bim antibody. (H) Kaplan-Meier survival plots of JMML patients with high or low expression of MORRBID. The purple line indicates the survival curve of children with JMML who had high expression of MORRBID (n = 10 patient samples: 8 with mutations in PTPN11, 1 in KRAS, and 1 in NRAS; age >18 months), and the green line indicates that of JMML children with low expression of MORRBID (n = 7 patient samples; 3 with mutations in PTPN11 and 4 in NRAS; age >18 months). The high expression of MORRBID was associated with poor overall survival of these patients (P = 0.049). See supplemental Figure 2 for the survival curve of JMML patients without mutations in PTPN11, KRAS, and NRAS. (I) Model for Morrbid regulation of myeloid cell survival in JMML. For mouse samples, n = 4 mice; for human samples, n = 7-10. *P < .05; **P < .01; ***P < .001; ****P < .0001.