SIM1

Single-minded homolog 1 also known as class E basic helix-loop-helix protein 14 (bHLHe14) is a protein that in humans is encoded by the SIM1 gene.

Function

SIM1 and SIM2 genes are homologs of Drosophila melanogaster single-minded (sim), so named because cells in the midline of the sim mutant embryo fail to properly develop and eventually die, and thus the paired longitudinal axon bundles that span the anterior-posterior axis of the embryo (analogous to the embryo's spinal cord) are collapsed into a "single" rudimentary axon bundle at the midline. Sim is a basic helix-loop-helix-PAS domain transcription factor that regulates gene expression in the midline cells. Since the sim gene plays an important role in Drosophila development and has peak levels of expression during the period of neurogenesis, it was proposed that the human SIM2 gene, which resides in a critical region of chromosome 21, is a candidate for involvement in certain dysmorphic features (particularly facial and skull characteristics), abnormalities of brain development, and/or mental retardation of Down syndrome.