Molecular cloning, sequence and expression pattern analysis of the mouse orthologue of the leukemia-associated guanine nucleotide exchange factor

Guanine nucleotide exchange factors (GEFs) of the Dbl family activate Rho proteins and thereby participate in diverse signaling pathways involving this family of small GTPases. However, specific role of Dbl-GEFs in developmental processes, particularly cell differentiation, remains largely unexplored. Recently, a novel member of the Dbl family, leukemia-associated Rho GEF factor (LARG), has been reported to be a fusion partner with mixed-lineage leukemia (MLL) protein in the acute myeloid leukemia, suggesting potential involvement of LARG in regulation of hematopoiesis. In this study, we describe the isolation of the cDNA copy and analysis of genomic structure and expression profile of the mouse orthologue of the human LARG gene. The mouse LARG (mLARG) gene contains 42 exons. The mLARG cDNA is 10,040 bp long and contains a 4631-bp open reading frame (ORF). The predicted mLARG protein shares an overall 89% identity with its human counterpart and contains the same functional domains, namely, Dbl homology (DH), pleckstrin homology (PH), PSD-95, Dlg and ZO-1/2 (PDZ) and regulator of G protein signaling (RGS) domains, as well as two putative signals of nuclear localization. The mLARG message is expressed in all tissues studied, with comparably higher expression levels observed in brain, lung, testis, liver and heart. Using amplified cDNA samples from sorted hematopoietic cells, we showed that mLARG is highly expressed in hematopoietic stem cell fractions, as well as in immature erythroid cells. These results demonstrate high similarity between mouse and human LARG proteins and genes and provide further support to the hypothesis of the potential involvement of LARG in regulation of early stages of hematopoiesis.