Transcription factor that may be a master gene of CNS development in cooperation with Arnt. It may have pleiotropic effects in the tissues expressed during development. Efficient DNA binding requires dimerization with another bHLH protein. Heterodimer of SIM2 and ARNT. Transcripts were detected in high levels in kidney followed by skeletal muscle and lung. Low levels were found in testis, brain and heart. In early fetal development it is found in CNS, developing kidney, tongue epithelium and cartilage primordia.