Role of Mash1-E Protein Heterodimers in Mash1 Function in the Developing Neural Tube
Neural-specific Class II bHLH transcription factors heterodimerize with ubiquitous Class I bHLH E proteins to form complexes required for neural differentiation. There are four known E proteins, HEB, E12, E47 and E2.2, in the mammalian nervous system, which potentially form heterodimers with Mash1 in the neural tube. To test the relevance of particular Mash1-E protein heterodimer combinations in vivo, I constructed tethered Mash1-E protein heterodimers for over-expression in the chick neural tube. By comparing overexpression of Mash1 with over-expression of these Mash1-E protein heterodimers, their abilities to effect neural differentiation and cell-type specification were analyzed. Mash1-E protein heterodimers are interchangeable in the function of driving neurogenesis in the chick neural tube. The effects of Mash1-E protein heterodimers on cell-type specificity were different, suggesting non-redundant functions in effecting dorsal interneuron populations. Furthermore, additional Mash1 heterodimer partners may be required for the cell-type specification function of Mash1.