Monoclonal antibodies identify a possible regulatory domain of MyoD1

A panel of monoclonal antibodies (mAbs) to murine MyoD1 was generated. One set of mAbs is shown to react with epitops(s) in the cysteine/histidine‐rich (C/H) region while another set is shown to reach with epitope(s) in the C‐terminal portion of MyoD1. One of the mAbs reactive with a C‐terminal epitope sensitively detected MyoD1 in whole cell extracts by Western blotting. Time course studies of total protein accumulation during C2C12 myoblast differentiation revealed only subtle change in the phosphorylation and quantity of MyoD1 protein present in C2C12 cells from induction to 120 hr after induction. These results suggest that modulation of MyoD1 protein or total phophorylation levels is not tightly associated with the transition of undifferentiated myoblasts to differentiated myocytes. Monoclonal antibodies to the C‐terminal epitope produces supershifted bands in gel retardation assays, indicating that these mAbs had no effect on DNA binding. Although the C/H region of MyoD1 does not participate in DNA binding, mAbs reactive with the C/H region neutralized this activity in gel retardation assays. These data suggest that the conserved C/H domain may serve to modulate MyoD1 DNA‐binding activity by interacting with another regulator. © 1992 Wiley‐Liss, Inc.