Homeobox Genes DataBase






Drosophila Genes in Development: Antp-like HOM
gene











Abdominal-B






Definition:




Function:

The Abdominal-B (Abd-B) gene, a member of the Drosophila bithorax
complex, is required during development to specify the identity of parasegments
10-14.


Abdominal-B is the last in linkage order and the most posterior acting
of the linked homeodomain proteins of the bithorax. Abdominal-B is unique
among the homeotics in that it is transcribed in two forms; a regulatory
(r) protein and a morphogenic (m) protein. Regulatory transcripts of Abdominal-B
act as repressors, suppressing embryonic ventral epidermal structures in
the 8th and 9th segments of the abdomen. Thus ABD-B r and m proteins are
critically involved in establishing cell fate in the tail segments of the
fly.


The distinction between r and m functions was based on the discovery
of three classes of regulatory mutations affecting Abdominal-B (Casanova,
1986). One class affects expression in five parasegments (10-14), a second
affects expression in only four (parasegments 10-13) and a third class
affects expression in just parasegment 14. The regulatory transcript of
ABD-B is thought to suppress the proximal morphogenetic (m) function (Casanova,
1986). The smaller r protein differs from its m counterpart in its lack
of an M repeat region. This is a particular amino acid segment that lies
upstream of the homeobox. The M repeat is rich in glutamines, a classical
transcription activation motif (De Lorenzi M., 1988).


Protein:

There are two variants to the ABD-B protein. One, a morphogenetic function
can be assigned to the 55 KD protein and a second, regulatory function
can be assigned to a 30 KD protein (Boulet, 1991).









Bithorax complex role in segmentation







Regulatory Regions:





hox Homeobox Clusters