The clustered Hox genes, which encode homeodomain transcription factors, control cell fates along the anterior-posterior axis. Differences between Hox proteins cause differences between body parts. Vertebrates have 13 Hox subgroups, called paralog groups, which can be correlated with some of the insect and Amphioxus genes, and have remained distinctive for hundreds of millions of years. We identify characteristic residues that define the different paralog groups. Some paralog groups can be recognized by the homeodomain sequence alone; others only by using characteristic residues outside the homeodomain. Mapping characteristic residues onto the known homeodomain crystal structure reveals that most of the homeodomain amino acids that distinguish paralog groups are oriented away from the DNA, in positions where they might engage in protein-protein interactions.
"Hox proteins reveal that sequences are highly vari- able outside the homeodomain (reviewed in Sharkey et al., 1997), suggesting that each Hox protein, or at least each Hox paralog group, may interact with a unique set of factors. Furthermore, the number of known Hox-interacting factors is large, and ever increasing, making it unlikely that all these factors interact with Hox complexes simultaneously. "
"functions. Specialised and common functions likely reflect the phylogeny of Hox proteins that derived through duplications from a unique or unique set of ancestral genes, leading up to 13 paraloguous groups in vertebrates (Sharkey et al., 1997). Following duplication , conservation of protein sequences likely allows for common function, while sequence divergence likely creates the frame for the acquisition of novel and distinct functions. "
[Show abstract][Hide abstract] ABSTRACT: Background:
Hox genes encode transcription factors playing important role in segment specific morphogenesis along the anterior posterior axis. Most work in the Hox field aimed at understanding the basis for specialised Hox functions, while little attention was given to Hox common function. In Drosophila, genes of the Bithorax complex [Ultrabithorax (Ubx), abdominalA (abdA), and AbdominalB (AbdB)] all promote abdominal identity. While Ubx and AbdA share extensive sequence conservation, AbdB is highly divergent, questioning how it can perform similar functions as Ubx and AbdA.
In this study, we investigate the genetic requirement for the specification of abdominal-type denticles by Ubx, AbdA, and AbdB. The impact of ectopic expression of Hox proteins in embryos mutant for Exd as well as of Wingless or Hedgehog signaling involved in intrasegmental patterning was analyzed. Results indicated that Ubx and AbdA do not require Exd, Wg, and Hh activity for specifying abdominal-type denticles, while AbdB does.
Our results support that distinct regulatory mechanisms underlie Ubx/AbdA- and AbdB-mediated specification of abdominal-type denticles, highlighting distinct strategies for achieving a similar biological output. This suggests that common function performed by distinct paralogue Hox proteins may also rely on newly acquired property, instead of conserved/ancestral properties.
"Homeotic/Hox genes were first identified in Drosophila, and encode transcription factors that play a pivotal role in giving a unique identity to each segment, thereby setting up morphogenesis along the anterior-posterior axis. The homeotic genes are evolutionarily conserved in organisms ranging from cnidarians to mammals (1). Loss-of-function mutants transform one segment into a copy of another segment (2,3). "
[Show abstract][Hide abstract] ABSTRACT: We have examined the effect of bithorax complex genes on the expression of castor gene. During the embryonic stages 12-15, both Ultrabithorax and abdominal-A regulated the castor gene expression negatively, whereas Abdominal-B showed a positive correlation with the castor gene expression according to real-time PCR. To investigate whether ABD-B protein directly interacts with the castor gene, electrophoretic mobility shift assays were performed using the recombinant ABD-B homeodomain and oligonucleotides, which are located within the region 10 kb upstream of the castor gene. The results show that ABD-B protein directly binds to the castor gene specifically. ABD-B binds more strongly to oligonucleotides containing two 5'-TTAT-3' canonical core motifs than the probe containing the 5'-TTAC-3' motif. In addition, the sequences flanking the core motif are also involved in the protein-DNA interaction. The results demonstrate the importance of HD for direct binding to target sequences to regulate the expression level of the target genes.
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