Three closely related Myb genes are present in vertebrate animals including mammals,
birds, amphibians, and bony fish. In the laboratory mouse, c-Myb is required
for blood cell production in the embryo and for intestinal maintenance in adults, A-Myb is required for
spermatogenesis and mammary gland proliferation, and B-Myb is required
very early in embryonic development. The invertebrate sea urchin and fruit
fly each have a single Myb gene most closely related to B-Myb of
vertebrates. In particular, the A-Myb and c-Myb proteins
contain a highly conserved central transcriptional activation domain not present
in B-Myb or the Myb proteins of invertebrates (1). In contrast, the
corresponding region of B-Myb has continued to evolve rapidly (2). These results
suggest that A-Myb and c-Myb arose by two gene duplications (red
occurred after the emergence of the vertebrate lineage. In support of this
hypothesis, we have recently found that B-Myb, but neither A-Myb
nor c-Myb, can complement the hemocyte defects in Drosophila
Myb null mutant larvae (3). Surprisingly,
the intensively studied nematode worm C elegans appears to have lost the Myb
gene during the course of evolution (4,5).
Key to protein cartoons: blue
boxes = tandem Myb repeats of DNA-binding domain; red boxes = transcriptional
activation domain; green boxes = conserved C-terminal regulatory domain.
1. Ganter B, Lipsick JS. Myb and
oncogenesis. Adv. Cancer Res. 76: 21-60 (1999).
2. Simon AL, Stone EA, Sidow A.
Inference of functional regions in proteins by quantification of evolutionary
constraints. Proc Natl Acad Sci U S A. 2002 99:2912-7 (2002).
CJ, Tirouvanziam R, Herzenberg LA, Lipsick JS. 2005. Functional evolution of the
vertebrate Myb gene family: B-Myb, but neither A-Myb nor c-Myb, complements
Drosophila Myb in hemocytes. Genetics 169: 215-229. [pdf].
4. Lipsick, JS. 2004. synMuv Verite--
Myb Comes Into Focus. Genes & Development 18: 2837-2844. [pdf]
H, Andrejka L, Ashton J, Karess R, Lipsick JS. 2008. Epigenetic regulation of
gene expression by Drosophila Myb and E2F2-RBF via the Myb-MuvB/dREAM complex.
Genes & Development 22: 601-614.