Trl-GAGA directly interacts with lola like and both are part of the repressive complex of Polycomb group of genes

Abstract

Epigenetic inheritance to maintain the expression state of the genome is essential during development. In Drosophila, the cis regulatory elements, called the Polycomb Response Elements (PREs) function to mark the epigenetic cellular memory of the corresponding genomic region with the help of PcG and trxG proteins. While the PcG genes code for the repressor proteins, the trxG genes encode activator proteins. The observations that some proteins may function both as PcG and trxG member and that both these group of proteins act upon common cis elements indicate at least a partial functional overlap among these proteins. Trl-GAGA was initially identified as a trxG member but later was shown to be essential for PcG function on several PREs. In order to understand how Trl-GAGA functions in PcG context, we have looked for the interactors of this protein. We identified lola like, aka batman, as a strong interactor of GAGA factor in a yeast two-hybrid screen. lolal also interacts with polyhomeotic and, like Trl, both lolal and ph are needed for iab-7PRE mediated pairing dependent silencing of mini-white transgene. These observations suggest a possible mechanism of how Trl-GAGA plays a role in maintaining the repressed state of target genes involving lolal, which may function as a mediator to recruit PcG complexes.

Drosophila BTB/POZ Domains of “ttk Group” Can Form Multimers and Selectively Interact with Each Other

“…As shown previously, the BTB domain of GAF can interact with BTB domains of Batman, 25,34 Pipsqueak, 26 Tramtrack, 23,33 and Mod(mdg4). 24 The question arises as to whether these BTB domains can interact with each other in different combinations.…”

“…[23][24][25][26] As controls, we used wellcharacterized BTB domains of human proteins Bcl6 and Miz1, which can form dimers 4 and tetramers, 10 respectively. We also examined the BTB domain of CP190, which has no significant homology to BTBs from the ttk group, and BTB from a vertebrate homolog of GAF identified recently.…”

“…Importantly, BTBs of several proteins from the ttk group can interact with the BTB of GAF. [22][23][24][25][26] One member of the ttk group, Mod(mdg4)-67.2 [Mod(mdg4)], interacts with the Su(Hw) protein and is involved in the enhancer-blocking activity of Su (Hw)-dependent insulators. The current model suggests an important role for Mod(mdg4) in the interaction between Su(Hw) insulators.…”

Drosophila retinal pigment cell death is regulated in a position-dependent manner by a cell memory gene

“…In genetic assays conducted previously, no dominant interactions were detectable between Trl and Pc or ph for the eye phenotype (our unpublished results), whereas a genetic interaction in Hox gene regulation was found between Trl and a second member of the PcG / trxG, lolal (Faucheux et al, 2003;Mishra et al, 2003). Since interactions have not been systematically tested between Trl and other PcG / trxG genes for the eye phenotype, it cannot be excluded that other members of these groups control cell death in the eye.…”

“…Two genes that share characteristics with both PcG and trxG genes, Trithorax-like (Farkas et al, 1994) (Trl) and lolal (also named batman, Faucheux et al, 2001;Faucheux et al, 2003;Mishra et al, 2003) were previously reported as displaying rough eyes in mutant escapers (Farkas et al, 1994;Faucheux et al, 2003) This phenotype could be reversed by introduction of trans- D,H,L). In Trl 13c escapers, the two horizontal sides (arrowheads in I,J,K) of each ommatidial hexagon appear shorter than the four oblique sides (arrows in I,J,K).…”