The higher survival rate observed in the adult Jak2 cKO mice is due to re-population of hematopoietic tissues with Jak2 expressing cells.

<p>(A) The levels of hemoglobin (Hb) plotted as a function of genotype and time. Although Hb levels dropped acutely in the Jak2 cKO mice (n = 7) relative to controls (n = 5) after TM injections, they returned to normal levels by day 147. (B) Shown are the relative levels of Jak2 mRNA in control (n = 3) and Jak2 cKO (n = 4) mice plotted as a function of day of collection, genotype, and tissue. (C) The levels of Hb plotted as a function of genotype and time. Shown are the control [Cre(-);f/f], Jak2 cKO [Cre(+);f/f], and the Jak2 compound mutant [Cre(+);f/Δ] genotypes. Conversion of one floxed Jak2 allele to a null allele [Cre(+);Jak2(f/Δ)] resulted in a marked and sustained reduction in Hb levels and ensuing death. *, p<0.05; **, p<0.01.