Transcription factor that regulates neurosecretory (NS) cell function and neuroendocrine cell fate. Acts as a master regulator of common NS functions such as Phm expression and neuropeptide production. Plays a role as a regulator of peptide-containing large dense-core vesicle (LDCV) production and peptidergic cell differentiation. Controls transcription of FMRFamide in Tv neuronal cells and Fur1 in Ap-let cells (Tvb and dorsal apterous cells). Also required for up-regulation of Phm in Tv and Ap-let cells, and expression of three neuropeptide genes, Ms, FMRFamide and Lk. Influences both regulated and constitutive secretory activity in neuroendocrine cells at embryonic and postembryonic level. Loss of function studies show reduced cellular levels of various neuropeptides and neuropeptide biosynthetic enzymes. Forms homodimers via the bHLH domain. These dimers bind the core E-box sequence. Detected in the developing nervous system in the bilateral domains in the cephalic region that later on forms part of the ring gland. Concomitantly expressed in the larval central nervous system (CNS), including the dorsal chain neurons as well as several bilateral clusters of neurons: large, midline protocerebral brain cells (MC), lateral protocerebral brain cells (LC), ventral subesophageal neurons (SE) and lateral abdominal neurons, and the transverse nerves. Outside the CNS, detected in at least three classes of endocrine cells: intrinsic cells of the corpora cardiaca, midgut cells, the Inka cells, lateral Bipolar neurons associated with the segmental transverse nerve, and several peptidergic cells of the enteric nervous system. Expressed only in central and peripheral neuroendocrine secretory cells and neurosecretory neurons but not in sensory or motor neurons. First detected in the embryonic ectoderm at early stage 11, but this expression is transient. Zygotic expression is first detected in stage 12 embryos and cytoplasmic expression is detected in many cells around stage 14. Embryonic cells maintain expression throughout their lifetime and expression continues into hatchling larvae less than 24 hours old. The basic domain binds to the canonical E-box (5'-CANNTG-3'), with a particular preference for TA relative to AT or CG in the variable central nucleotide positions. Extended N-terminus. Extended N-terminus.