Suppressor screen in Mpl ^-/- mice: c-Myb mutation causes supraphysiological production of platelets in the absence of thrombopoietin signaling

Abstract

Genetic screens in lower organisms, particularly those that identify modifiers of preexisting genetic defects, have been used successfully to order components of complex signaling pathways. To date, similar suppressor screens have not been used in vertebrates. To define the molecular pathways regulating platelet production, we have executed a large-scale modifier screen with genetically thrombocytopenic Mpl ؊/؊ mice by using N-ethyl-N-nitrosourea mutagenesis. Here we show that mutations in the c-Myb gene cause a myeloproliferative syndrome and supraphysiological expansion of megakaryocyte and platelet production in the absence of thrombopoietin signaling. This screen demonstrates the utility of large-scale N-ethyl-N-nitrosourea mutagenesis suppressor screens in mice for the simultaneous discovery and in vivo validation of targets for therapeutic discovery in diseases for which mouse models are available.

Mutations in Multiple Domains of c-Myb Disrupt Interaction with CBP/p300 and Abrogate Myeloid Transforming Ability

“…6A). The c-Myb 3M, PLT3, and PLT4 mutants possessed comparable activities with that of the WT in contrast to lower activity from the PLT4 mutant reported by Carpinelli et al (4). Surprisingly, the double-domain mutants (3M.CT3 and 3M.L3,4P) exhibited minimal transactivation ability, which was substantially less than that of the WT and CT3 Myb forms.…”

“…c-myb-null mice display abnormal fetal liver hematopoiesis and die by day 15 of gestation due to severe anemia (3). Moreover, ENU mutagenesis studies in mice revealed point mutations in myb that resulted in hypomorphic alleles and consequent hematopoietic irregularities (4,5).…”

Proper expression of the Gcn5 histone acetyltransferase is required for neural tube closure in mouse embryos

“…Similarly, Ski deficiency resulted in a high penetrance (83%) of exencephaly in a 129p2 background but a low penetrance (5-6%) in the C57BL6 strain (Colmenares et al, 2002). Genetic variation of NTDs in mouse likely reflects the additive effects of several mutant genes, and additional mutagenesis may be required to define factors that affect the penetrance of NTDs in the presence of defective alleles of Gcn5 (for example, see Carpinelli et al, 2004). Genetic variations also likely underlie different susceptibilities to NTDs in humans (Zohn et al, 2005).…”

Uncovering the uncharacterized and unexpected: Unbiased phenotype‐driven screens in the mouse

“…Modifier screens have proven extremely powerful in yeast, worms, and flies to dissect complex biological questions. A dominant modifier screen in the mouse found two alleles that suppressed the lack of platelets found in Mpl homozygous deletion mice (Carpinelli et al, 2004). Modifier screens take time and careful planning, as mouse production must be ramped up so that there are enough animals available for the screening crosses.…”