Epigenetic control of lineage choice/differentiation:
The last decade of work and the recent Nobel prize awarded for reprogramming has made it clear that cell identity is established and maintained by combinations of transcription factors. A role for epigenetic regulators such as histone methyltransferases in establishing and maintaining cell fate has been hypothesized, but investigations of the role of these enzymes in complex biological systems have lagged behind their biochemical characterization. To bridge such gap, we have generated floxed alleles of two SET-domain (methyltransferase) containing genes encoding for putative methytransferases. Based on in vitro experiments SET7/9 had been described as a H3K4 monomethyltransferase (now questioned) capable of methylating a number of important transcription factors including p53 and the estrogen receptor. Despite reports that SET7 activity is a requirement for these transcription factors to function, KO mice for SET7/9 were viable, fertile and did not display any defect in p53 pathways. As these data was controversial and anti-dogmatic, it took over three years of a rather byzantine review process for this work to be published. This should function as a cautionary tale on the dangers of basing strong biological conclusions on in vitro data, and as a message to reviewers and editors that resistance is futile, and that eventually the truth will prevail and they will publish our papers! Further investigations in the role of SET7/9 are ongoing in collaboration with the Zaph laboratory.
EHMT2/G9a is a H3K9 dimethyltransferase, although it has been suggested that it may also methylate other residues on histone tails. Complete KO of this enzyme was shown to lead to early lethality, prompting us to generate a floxed allele to analyze its roles in adult organisms.
In particular, we have focused on the analysis of its role in hematopoiesis. To our surprise, G9a deletion did not lead to an overt phenotype, and although alterations in T-cell polarization were characterized and reported by our next-door collaborator Colby Zaph, no defect in stem cells activity was observed when using sensitive competitive transplantation assays.
The first hint of a G9a dependent phenotype in immature hematopoietic cells stemmed from the observation that the colonies formed by G9a KO bone marrow derived progenitors when plated in methylcellulose were significantly smaller than those obtained from control heterozygous animals. This led us to test the role of G9a in leukemia, and eventually to the finding that G9a is required for aggressive acute myeloid leukemia, and that in its absence leukemic cells differentiate at a high rate.
EHMT2/G9a is a H3K9 dimethyltransferase, although it has been suggested that it may also methylate other residues on histone tails. Complete KO of this enzyme was shown to lead to early lethality, prompting us to generate a floxed allele to analyze its roles in adult organisms.
In particular, we have focused on the analysis of its role in hematopoiesis. To our surprise, G9a deletion did not lead to an overt phenotype, and although alterations in T-cell polarization were characterized and reported by our next-door collaborator Colby Zaph, no defect in stem cells activity was observed when using sensitive competitive transplantation assays.
The first hint of a G9a dependent phenotype in immature hematopoietic cells stemmed from the observation that the colonies formed by G9a KO bone marrow derived progenitors when plated in methylcellulose were significantly smaller than those obtained from control heterozygous animals. This led us to test the role of G9a in leukemia, and eventually to the finding that G9a is required for aggressive acute myeloid leukemia, and that in its absence leukemic cells differentiate at a high rate.
