HIPP1 stabilizes the interaction between CP190 and Su(Hw) in the Drosophila insulator complex

Abstract

Suppressor of Hairy-wing [Su(Hw)] is one of the best characterized architectural proteins in Drosophilaand recruits the CP190 and Mod(mdg4)-67.2 proteins to chromatin, where they form a well-known insulator complex. Recently, HP1 and insulator partner protein 1 (HIPP1), a homolog of the human co-repressor Chromodomain Y-Like (CDYL), was identified as a new partner for Su(Hw). Here, we performed a detailed analysis of the domains involved in the HIPP1 interactions with Su(Hw)dependent complexes. HIPP1 was found to directly interact with the Su(Hw) C-terminal region (aa 720-892) and with CP190, but not with Mod(mdg4)-67.2. We have generated Hipp1 null mutants (Hipp Δ1 ) and found that the loss of Hipp1 does not affect the enhancer-blocking or repression activities of the Su(Hw)-dependent complex. However, the simultaneous inactivation of both HIPP1 and Mod(mdg4)-67.2 proteins resulted in reduced CP190 binding with Su(Hw) sites and significantly altered gypsy insulator activity. Taken together, these results suggested that the HIPP1 protein stabilized the interaction between CP190 and the Su(Hw)-dependent complex.Insulators in Drosophila and vertebrate genomes have been identified based on their abilities to disrupt communications between enhancers and promoters, when inserted between them, and to prevent the repression mediated by heterochromatin 1-5 . In the past few years, a special class of architectural proteins has been identified, including some well-known insulator proteins, that are responsible for global chromosomal architecture and the local regulation of enhancer-promoter interactions 6,7 . Insulator proteins are involved in the formation of topologically associated domains, which are the fundamental structural elements of the eukaryotic genome [8][9][10][11] .Today, Suppressor of Hairy-wing [Su(Hw)] is one of the best-characterized insulator proteins in Drosophila. The Su(Hw) insulator was first identified in the gypsy retrotransposon, which contains a 460-bp sequence with 12 degenerate octamer binding sites for the Su(Hw) 12,13 . The best-characterized insulator complex consists of the Su(Hw) protein and its partners, Mod(mdg4)-67.2 and CP190 14-18 . The CP190 and Mod(mdg4)-67.2 proteins are recruited to chromatin through interactions with each other and with the Su(Hw) protein 19,20 .The Su(Hw) protein is ubiquitously expressed throughout development and contains an array of 12 C 2 H 2 -type zinc finger (ZF) domains 21,22 . The 6-9 ZF domains specifically recognize a 12-bp motif 23 . In previous genome-wide studies, three classes of Su(Hw) binding regions have been identified, which are characterized by whether they bind Su(Hw) alone (SBS-O), bind both Su(Hw) and CP190 (SBS-C), or bind all three proteins (SBS-CM) [24][25][26][27] . CP190 and Mod(mdg4)-67.2 both assist the Su(Hw) complex when binding to SBS-CM sites 19,20 .The Su(Hw) C-terminal domain (aa 716-892) is responsible for both insulator function 15,21,22 and the repression of neuronal genes in oocytes 28 . Like the gypsy insulator, artificia...

A Phosphorylated Histone H2A Variant Displays Properties of Chromatin Insulator Proteins inDrosophila

“…As interactions between insulator proteins are generally required for canonical insulator functions (Geyer and Corces, 1992, Bonchuk et al, 2015, Golovnin et al, 2016, Melnikova, Kostyuchenko, Parshikov, et al, 2018, Melnikova et al, 2019), we examined the relationship between each of these insulator proteins and γH2Av in various insulator mutant backgrounds. Notably, the colocalization between Mod(mdg4)67.2 and γH2Av was strongly reduced in the su(Hw) e04061 background (Figure 3A, F).…”

“…Centrosomal Protein 190 (CP190), another essential component of the gypsy insulator (Pai et al, 2004), was originally described through its activity during the cell cycle, dissociating from chromatin during mitotic prophase and localizing to the centrosome (Ooegema et al, 1995). In chromatin, CP190 is found as an essential part of different insulator complexes (Bushey et al, 2009) and is recruited to the gypsy insulator through interactions with Mod(mdg4)67.2 (Pai et al, 2004) and the amino terminal domain of HIPP1 (HP1 and insulator partner protein 1) (Melnikova et al, 2019). HIPP1 is the most recently described member of the gypsy insulator complex (Alekseyenko et al, 2014) and functions to stabilize the interaction between Su(Hw) and CP190, but is not required for insulator activity or transcriptional regulation (Glenn and Geyer, 2019, Melnikova et al, 2019).…”

Chromatin Remodelers in the 3D Nuclear Compartment

“…These data suggest that although dCTCF cannot recruit the cohesin complex for the formation of chromatin loops, it is possible that this protein binds to other architectural proteins that are exclusive to the fly and thus, delimits the formation of different domains in the genome ( van Bortle and Corces, 2012 ). Furthermore, genetic and biochemical evidence demonstrates that some of these proteins act in complexes, and are distributed along the genome in different combinations, which provides specificity in the regulation of gene expression ( Gerasimova et al, 1995 ; Melnikova et al, 2004 , 2017 , 2019 ; Soshnev et al, 2013 ; Vogelmann et al, 2014 ; Glenn and Geyer, 2019 ; Kirchanova et al, 2019 ).…”

Insights into HP1a-Chromatin Interactions

“…Its location is mainly pericentric, but it also binds to several euchromatin regions and interacts with AP proteins such as Su(Hw), Mod(mdg4), and CP190 [199]. HIPP1 functions stabilize the interactions between CP190 and the Su(Hw)-dependent complex [200]. In this article, we include HIPP1 as a possible architectural protein in Table 3, although this function has not yet been fully demonstrated.…”