Spermiogenesis and Male Fertility Require the Function of Suppressor of Hairy-Wing in Somatic Cyst Cells of Drosophila

NF-κB factors cooperate with Su(Hw)/E4F1 to balance Drosophila/human immune responses via modulating dynamic expression of miR-210

MicroRNAs (miRNAs) play crucial regulatory roles in controlling immune responses, but their dynamic expression mechanisms are poorly understood. Here, we firstly confirm that the conserved miRNA miR-210 negatively regulates innate immune responses of Drosophila and human via targeting Toll and TLR6, respectively. Secondly, our findings demonstrate that the expression of miR-210 is dynamically regulated by NF-κB factor Dorsal in immune response of Drosophila Toll pathway. Thirdly, we find that Dorsal-mediated transcriptional inhibition of miR-210 is dependent on the transcriptional repressor Su(Hw). Mechanistically, Dorsal interacts with Su(Hw) to modulate cooperatively the dynamic expression of miR-210 in a time- and dose-dependent manner, thereby controlling the strength of Drosophila Toll immune response and maintaining immune homeostasis. Fourthly, we reveal a similar mechanism in human cells, where NF-κB/RelA cooperates with E4F1 to regulate the dynamic expression of hsa-miR-210 in the TLR immune response. Overall, our study reveals a conservative regulatory mechanism that maintains animal innate immune homeostasis and provides new insights into the dynamic regulation of miRNA expression in immune response.

The Functions and Mechanisms of Action of Insulators in the Genomes of Higher Eukaryotes

The mechanisms underlying long-range interactions between chromatin regions and the principles of chromosomal architecture formation are currently under extensive scrutiny. A special class of regulatory elements known as insulators is believed to be involved in the regulation of specific long-range interactions between enhancers and promoters. This review focuses on the insulators of Drosophila and mammals, and it also briefly characterizes the proteins responsible for their functional activity. It was initially believed that the main properties of insulators are blocking of enhancers and the formation of independent transcription domains. We present experimental data proving that the chromatin loops formed by insulators play only an auxiliary role in enhancer blocking. The review also discusses the mechanisms involved in the formation of topologically associating domains and their role in the formation of the chromosomal architecture and regulation of gene transcription.

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

Suppressor of Hairy-wing [Su(Hw)] is one of the best characterized architectural proteins in Drosophila and 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.

The same domain of Su(Hw) is required for enhancer blocking and direct promoter repression

Suppressor of Hairy-wing [Su(Hw)] is a DNA-binding architectural protein that participates in the organization of insulators and repression of promoters in Drosophila. This protein contains acidic regions at both ends and a central cluster of 12 zinc finger domains, some of which are involved in the specific recognition of the binding site. One of the well-described in vivo function of Su(Hw) is the repression of transcription of neuronal genes in oocytes. Here, we have found that the same Su(Hw) C-terminal region (aa 720–892) is required for insulation as well as for promoter repression. The best characterized partners of Su(Hw), CP190 and Mod(mdg4)-67.2, are not involved in the repression of neuronal genes. Taken together, these results suggest that an unknown protein or protein complex binds to the C-terminal region of Su(Hw) and is responsible for the direct repression activity of Su(Hw).

Investigation of the Developmental Requirements of Drosophila HP1 and Insulator Protein Partner, HIPP1

Drosophila Suppressor of Hairy-wing [Su(Hw)] is a multifunctional zinc finger DNA binding protein. Transcriptional regulation by Su(Hw) is essential in the ovary and testis, where Su(Hw) functions primarily as a repressor. Recently, the HP1a and Insulator Partner Protein 1 (HIPP1) was found to extensively co-localize with Su(Hw) and other insulator binding proteins in euchromatic regions of the genome, and with Heterochromatin Protein 1a (HP1a) in heterochromatic regions. As HIPP1 is the homolog of the human co-repressor Chromodomain Y-Like (CDYL), we tested its requirement in establishing transcriptional repression in flies. To this end, we generated multiple Hipp1 null alleles and a tagged derivative of the endogenous gene (Hipp1GFP ), using CRISPR mutagenesis. We show that HIPP1 is a widely expressed nuclear protein that is dispensable for viability, as well as female and male fertility. We find that HIPP1 and HP1a display minimum co-localization in interphase cells, and HP1a-dependent transcriptional repression of several reporter genes is HIPP1-independent, indicating that HIPP1 is not essential for HP1a-dependent heterochromatin formation. Despite Su(Hw) having a major role in promoting HIPP1 occupancy in euchromatin, we show that HIPP1 is dispensable for the transcriptional and insulator functions of Su(Hw), indicating that HIPP1 is not a critical Su(Hw) cofactor. Further studies are needed to clarify the role of HIPP1 in Drosophila development.