broadcomplex

Broad-Complex, commonly abbreviated BR-C, is a gene family in insects that encodes a set of transcription factors responsive to the steroid hormone ecdysone. In Drosophila melanogaster and other insects, BR-C proteins regulate the timing and progression of metamorphosis by controlling the expression of genes involved in molting, tissue remodeling, and cuticle formation following ecdysone pulses.

BR-C comprises multiple isoforms generated by alternative promoters and splicing, typically referred to as BR-C Z1, Z2, Z3, and Z4. Each isoform shares an N-terminal region but carries a distinct C-terminal zinc finger DNA-binding domain, enabling different sets of target genes and tissue-specific effects during development.

Expression of BR-C is induced by the ecdysone receptor complex (EcR/USP) in response to a molt-inducing hormonal pulse. BR-C acts downstream of early response genes such as E74 and E75 and functions to regulate late-response genes that execute metamorphic processes, including imaginal disc differentiation and cuticle biosynthesis. Loss-of-function BR-C mutations disrupt normal metamorphosis, causing delayed or defective pupariation and developmental abnormalities.

BR-C genes and proteins are conserved across insects, with homologs identified in many species. The BR-C program exemplifies how steroid hormones orchestrate developmental transitions, and BR-C serves as a useful genetic marker for studying ecdysone signaling and metamorphic development in insect models.