Antp P1 control causes ectopic expression of pb in the ventral nerve cord of the posterior prothorax, mesothorax and metathorax in a pattern that closely resembles that of wild type Antp protein. Spatially correct but reduced pb protein expression is also observed.

(Cribbs et al., 1992)

pb protein expression was assayed with antibodies to a pb/lacZ fusion protein. pb protein is first detected between 5.5 and 6hrs in a group of nuclei in the presumptive mesoderm behind the stomodeum. pb protein expression in the mesoderm is dynamic and the expressing cells migrate away from the ventral midline, separating into two groups. After hour 7, expression is observed in 6-8 cells internal to each manidibular lobe. Subsequently, staining is observed in a group of cells that become positioned along the walls of the foregut. Staining is also observed in the labial and maxillary lobes. By the end of germ band retraction, staining in the labial lobes and sternal region is quite intense. Staining in the maxillary and mandibular lobes has also become intense. By about 10hrs, staining is also observed in a group of cells in the vicinity of the posterior foregut which are later found around the esophagus and proventriculus. Expression in the gnathal segments remains strong during head involution. pb protein begins to be expressed in the CNS in a pattern that becomes increasingly complex. It is expressed in a subset of cells in the supraesophageal ganglion, the subesophageal ganglion, and in the ventral nerve cord. Distinct patterns of pb expression are observed in the CNS of the thoracic segments, the first six abdominal segments, and the more posterior abdominal segments.

(Pultz et al., 1988)