Homeobox Genes DataBase

Drosophila Genes in Development: Gap gene family

cap'n'collar

Function

Early in head differentiation the anterior posterior axis is marked by a subdivision into seven segments. The element primarily responsible for this subdivision is the action of gap genes, expressed in well defined anterior-posterior positions. Among the gap genes, buttonhead regulates cnc activation. cnc regulates genes responsible for labrial and mandibular development, specifically in the dorsal portion of the labrial segment and the posterior lateral and ventral portion of the mandibular segment. cnc acts as a segment-specific selector gene controlling the identity of two cephalic segments. cnc also functions in conjunction with Deformed, a homeotic gene expressed in the head.

cnc represses maxillary development in the mandibular segment. cnc defines the dorsal pharyngeal region and the posterior lateral and ventral portion of the pharynx (Mohler J., 1995).

cnc is responsible for the maintenance of wg in the dorsal pharyngeal domain of wingless expression (Mohler J., 1995).

Protein

bZIP transcription factor is closely related to the mammalian erythroid factor NF-E2 (p45). The leucine zipper of CNC is longer than bZIP proteins and contains six heptad repeats. The function of the leucine zipper is considered as a protein interaction domain. The leucine zipper of CNC is divergent from the typical sequence (Mohler J., 1991).

Subcellular location

Nuclear

Expression Patterns

cnc is expressed in the labrial region of the foregut, fated to give rise to the dorsal pharynx.

cnc is initially expressed in the blastoderm embryo in an anterior dorsal cap and in a 3-4 cell wide stripe at about 70% egg length just anterior to the cephalic furrow. Expression in the regions of the labral segment, mandibular segment, and intercalary segment continues through the extended germ band stage and for the latter two regions, throughout embryogenesis (Mohler J., 1991).

cap'n'collar expression in the anterior compartment of the mandibular segment has two roles, depending on whether or not Deformed is expressed. Where Deformed is not expressed, cnc promotes hypopharyngeal development of the mandibular segment. Where Deformed is expressed, cnc promotes mandibular development in combination with Deformed (Mohler J., 1995).