Biology subjects

Hildebrandt, R. P.

Publications and source records attributed to Hildebrandt, R. P..

3 recordsLinked to original sources

bioRxiv2026

Muscleblind-like proteins dimerize by forming disulfide bonds to regulate alternative splicing and pathogenic RNA foci formation

Muscleblind-like (MBNL) RNA-binding proteins (RBPs) possess modular domains that mediate regulation of alternative splicing and RNA localization. Myotonic Dystrophy Type 1 is a CTG repeat expansion disorder where MBNL is sequestered into intranuclear RNA foci, impairing its function. Previous studies found that MBNL self-associates through its exon 7, but the nature of this interaction is not well understood. We identified a cysteine in MBNL1 exon 7 that enables dimerization through formation of an intermolecular disulfide bond. We likewise demonstrate that MBNL2 dimerizes by forming disulfide bonds between multiple cysteines in its carboxy-terminus. Nucleocytoplasmic fractionation revealed a greater proportion of MBNL1 dimer in the nucleus, suggesting a nuclear function for the MBNL1 dimer. We investigated a connection between MBNL1 dimerization and MBNL1-mediated regulation of alternative splicing. To accomplish this, we mutated the MBNL1 cysteine in question to alanine (C325A) and performed RNAseq. We uncovered novel splicing events sensitive to MBNL1 dimerization. We also found that MBNL1 C325A, when co-expressed with expanded CTG repeats, produces smaller, more numerous foci, suggesting a role for the MBNL1 dimer in maintaining foci integrity. These results provide insight into biological and pathological mechanisms of MBNL1 dimerization and suggest other RBPs might similarly dimerize to regulate function. GRAPHICAL ABSTRACT

molecular biology↗

bioRxiv2022

Muscleblind-like proteins use modular domains to localize RNAs by riding kinesins and docking to membranes

RNA transport and local translation provide spatial control of gene expression, and RNA binding proteins (RBPs) act as critical adapters in this multi-step process. Muscleblind-like (MBNL) RNA binding proteins, implicated in myotonic dystrophy and cancer, localize RNAs to myoblast membranes and distal neurites through unknown mechanisms. We found that MBNL forms motile and anchored granules in neurons and myoblasts, and selectively associates with kinesins Kif1b and Kif1c through its zinc finger (ZnF) domains. Other RBPs with similar ZnFs also associate with these kinesins, implicating a motor-RBP specificity code. Live cell imaging and fractionation revealed that membrane anchoring is mediated through the unstructured carboxy-terminal tail of MBNL1. Both kinesin- and membrane-recruitment functions were reconstituted using MBNL-MS2 coat protein fusions. This approach, termed RBP Module Recruitment and Imaging (RBP-MRI), decouples RNA binding, kinesin recruitment, and membrane anchoring functions, while also establishing general strategies for studying multi-functional, modular domains of RBPs.

cell biology↗

bioRxiv2020

Transcriptome Alterations in Myotonic Dystrophy Frontal Cortex

Myotonic dystrophy (dystrophia myotonica, DM) is caused by expanded CTG/CCTG microsatellite repeats, leading to multi-systemic symptoms in skeletal muscle, heart, gastrointestinal, endocrine, and central nervous systems (CNS), among others. For some patients, CNS issues can be as debilitating or more so than muscle symptoms; they include hypersomnolence, executive dysfunction, white matter atrophy, and neurofibrillary tangles. Although transcriptomes from DM type 1 (DM1) skeletal muscle have provided useful insights into pathomechanisms and biomarkers, limited studies of transcriptomes have been performed in the CNS. To elucidate underlying causes of CNS dysfunction in patients, we have generated and analyzed RNA-seq transcriptomes from the frontal cortex of 21 DM1 patients, 4 DM type 2 (DM2) patients, and 8 unaffected controls. One hundred and thirty high confidence splicing changes were identified, most occurring exclusively in the CNS and not in skeletal muscle or heart. Mis-spliced exons were found in neurotransmitter receptors, ion channels, and synaptic scaffolds, and we identified an alternative exon in GRIP1 that modulates association with kinesins. Splicing changes exhibited a gradient of severity correlating with CTG repeat length, as measured by optical mapping of individual DNA molecules. All individuals studied, including those with modest splicing defects, showed extreme somatic mosaicism, with a subset of alleles having >1000 CTGs. Analyses of gene expression changes showed up-regulation of genes transcribed in microglia and endothelial cells, suggesting neuroinflammation, and downregulation of genes transcribed in neurons. Gene expression of RNAs encoding proteins detectable in cerebrospinal fluid were also found to correlate with mis-splicing, with implications for CNS biomarkers of disease severity. These findings provide a framework for future mechanistic and therapeutic studies of CNS issues in DM.

genetics↗