DEC1 is a 412 amino acid, basic helix-loop-helix (bHLH) containing protein that is involved in the control of proliferation and/or differentiation of several cell types including nerve cells, fibroblasts and chondrocytes. The bHLH region of DEC1 is structurally similar to the bHLH regions of the mammalian HES family, Drosophila hairy and Drosophila Enhancer of split m7. DEC1 is a novel direct target for cAMP in a wide range of cells, and is involved in the control of gene expression in cAMP-activated cells. DEC2, also known as SHARP1, is highly expressed in skeletal muscle and brain. The gene encoding human DEC2 maps to chromosome 12p11.23-p12.1. DEC1 and DEC2 play a role in regulating the mammalian molecular clock by suppressing the transcription of specific clock genes. Both DEC1 and DEC2 are detected in the suprachiasmimc nucleus in a circadian fashion. Brief light impulses induce the expression of DEC1 in a phase-dependent manner.