Bartkuhn, M. | bioRxiv Science

bioRxiv2022

The H2A.Z.1/PWWP2A/NuRD-associated protein HMG20A controls early head and heart developmental transcription programs

Abstract/SummarySpecialized chromatin-binding proteins are required for DNA-based processes during development. We recently established PWWP2A as direct histone variant H2A.Z interactor involved in mitosis and cranial-facial development. Here, we identify the H2A.Z/PWWP2A-associated protein HMG20A as part of several chromatin-modifying complexes including NuRD, and show that it localizes to genomic regulatory regions. Hmg20a depletion causes severe head and heart developmental defects in Xenopus laevis. Our data indicate that craniofacial malformations are caused by defects in neural crest cell (NCC) migration and cartilage formation. These developmental defects are pheno-copied in HMG20A-depleted mESCs, which show inefficient differentiation into NCCs and cardiomyocytes (CMs). Accordingly, loss of HMG20A caused striking deregulation of transcription programs involved in epithelial- mesenchymal transition (EMT) and cardiac differentiation, thereby providing insights into the regulatory circuits controlled by HMG20A. Collectively, our findings implicate HMG20A as part of the H2A.Z/PWWP2A/NuRD-axis and reveal it as a key modulator of the intricate developmental transcription programs that guide NCC and cardiomyocyte differentiation.

molecular biology↗

bioRxiv2022

The structure, binding, and function of a Notch transcription complex involving RBPJ and the epigenetic reader protein L3MBTL3

The highly conserved Notch pathway transmits signals between neighboring cells to elicit distinct downstream transcriptional programs. In given contexts, Notch is a major regulator of cell fate specification, proliferation, and apoptosis, such that aberrant Notch signaling leads to a pleiotropy of human diseases, including developmental disorders and cancers. The canonical pathway signals through the transcription factor CSL (RBPJ in mammals), which forms a transcriptional activation complex with the intracellular domain of the Notch receptor and the coactivator Mastermind. CSL can also function as a transcriptional repressor by forming complexes with one of several different corepressor proteins, such as FHL1 or SHARP in mammals and Hairless in Drosophila. Recently, we identified the malignant brain tumor (MBT) family member L3MBTL3 as a bona fide RBPJ binding corepressor that recruits the repressive lysine demethylase LSD1/KDM1A to Notch target genes. Here we define the RBPJ-interacting domain (RBP-ID) of L3MBTL3 and report the 2.06 [A] crystal structure of the complex formed between RBPJ, the RBP-ID of L3MBTL3 and DNA. The structure reveals the molecular interactions underlying L3MBTL3 complexation with RBPJ, which we comprehensively analyze with a series of L3MBTL3 and RBPJ mutations that span the binding interface. Compared to other RBPJ-binding proteins, we find that L3MBTL3 interacts with RBPJ via an unusual binding motif, which is sensitive to mutations throughout its RBPJ-interacting region. We also show that these disruptive mutations affect RBPJ and L3MBTL3 function in cells, providing further insights into Notch mediated transcriptional regulation.

biochemistry↗