It's a Yolk, Son
Unlike most other oncogenes, v-Myb is capable of transforming blood cells but not fibroblasts. However, it is very difficult to introduce cloned DNA directly into primary hematopoietic cells. Therefore, we have developed a system in which a retrovirus carrying both a dominantly selectable marker gene (neo) and a particular Myb gene is used to produce an infectious virus (the small particles budding from the infected cell in the electron micrograph, below left).
Embryonic yolk sac cells contain many precursors of the myelomonocytic lineage. These cells normally differentiate and stop dividing when cultured (center panel, above), however, v-Myb can block their differentiation and cause their growth to continue in a fashion similar to leukemia (right panel, above). This assay has been used to characterize a variety of mutant forms of the v-Myb and c-Myb proteins in order to map protein domains and to correlate protein structure and function. One general conclusion of these studies is that transcriptional regulation by Myb proteins is necessary but not sufficient for transformation.
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