The Drosophila hairy and Enhancer of split genes encode basic helix-loop-helix (bHLH) transcriptional repressors that function in the Notch signaling pathway and control segmentation and neural development during embryogenesis. The Notch signaling pathway is thought to maintain stem cells through transcriptional activation of HES/HEY family members to repress tissue-specific transcription factors. HESL (HES-like), also known as Mgn or HELT (HES/HEY-like transcription factor), is a 327 amino acid nuclear protein belonging to the HEY family. Containing a basic helix-loop-helix (bHLH) domain and an Orange domain, HESL self-associates and interacts with HES5 and HRT2. HESL is considered a transcriptional repressor that binds to the canonical E box sequence 5'-CACGCG-3'. HESL exists as two isoforms produced by alternative splicing events.