Biology subjects

Yeom, K.-H.

Publications and source records attributed to Yeom, K.-H..

4 recordsLinked to original sources

bioRxiv2024

The lncRNA Malat1 is trafficked to the cytoplasm as a localized mRNA encoding a small peptide in neurons.

Synaptic function is modulated by local translation of mRNAs that are transported to distal portions of axons and dendrites. The Metastasis-associated lung adenocarcinoma transcript 1 (MALAT1) is broadly expressed across cell types, almost exclusively as a nuclear non-coding RNA. We found that in differentiating neurons, a portion of Malat1 RNA redistributes to the cytoplasm. Depletion of Malat1 from neurons stimulated expression of particular pre- and post-synaptic proteins, implicating Malat1 in their regulation. Neuronal Malat1 is localized to both axons and dendrites in puncta that co-stain with Staufen1 protein, similar to neuronal granules formed by locally translated mRNAs. Ribosome profiling of mouse cortical neurons identified ribosome footprints within a region of Malat1 containing short open reading frames. The upstream-most reading frame (M1) of the Malat1 locus was linked to the GFP coding sequence in mouse ES cells. When these gene-edited cells were differentiated into glutamatergic neurons, the M1-GFP fusion protein was expressed. Antibody staining for the M1 peptide confirmed its presence in wildtype neurons, and showed enhancement of M1 expression after synaptic stimulation with KCL. Our results indicate that Malat1 serves as a cytoplasmic coding RNA in the brain that is both modulated by and modulates synaptic function.

molecular biology↗

bioRxiv2023

Alternative splicing of a chromatin modifier alters the transcriptional regulatory programs of stem cell maintenance and neuronal differentiation

Development of embryonic stem cells (ESCs) into neurons requires intricate regulation of transcription, splicing, and translation, but how these processes interconnect is not understood. We found that polypyrimidine tract binding protein 1 (PTBP1) alters splicing of DPF2, a subunit of BAF chromatin remodeling complexes. Dpf2 exon 7 is inhibited by PTBP1 to produce the DPF2-S isoform early in development. During neuronal differentiation, loss of PTBP1 allows exon 7 splicing, resulting in a longer DPF2-L isoform. Gene expression changes are induced by DPF2-L in ESC, and by DPF2-S in neurons. In ESC, chromatin immunoprecipitation locates DPF2-S but not DPF2-L at sites bound by pluripotency transcription factors. In neuronal progenitors, DPF2-S sites coincide with NFI protein binding, and DPF2-L sites with CTCF. DPF2-S sites show enhancer chromatin modifications, while DPF2-L sites show modifications associated with promoters. In sum, alternative splicing events during neuronal development impact chromatin organization by altering BAF complex targeting.

molecular biology↗

bioRxiv2023

Improved enzymatic labeling of fluorescent in situ hybridization probes applied to the visualization of retained introns in cells

Fluorescence In Situ Hybridization (FISH) is a widely used tool for quantifying gene expression and determining the location of RNA molecules in cells. Here, we present an improved method for FISH probe production that yields high purity probes with a wide range of fluorophores using standard laboratory equipment at low cost. The method modifies an earlier protocol that uses terminal deoxynucleotidyl transferase to add fluorescently labeled nucleotides to synthetic deoxyoligonucleotides. In our protocol, Amino-11-ddUTP is joined to an oligonucleotide pool prior to its conjugation to a fluorescent dye, thereby generating pools of probes ready for a variety of modifications. This order of reaction steps allows for high labeling efficiencies regardless of the GC content or terminal base of the oligonucleotides. The Degree Of Labeling (DOL) for spectrally distinct fluorophores (Quasar, ATTO and Alexa dyes) was mostly greater than 90%, comparable to commercial probes. The ease and low cost of production allowed generation of probe-sets targeting a wide variety of RNA molecules. Using these probes, FISH assays in C2C12 cells showed the expected subcellular localization of mRNAs and pre-mRNAs for Polr2a (RNA polymerase II subunit 2a) and Gapdh, and of the long noncoding RNAs Malat1 and Neat1. Developing FISH probe sets for several transcripts containing retained introns, we found that retained introns in the Gabbr1 and Noc2l transcripts are present in subnuclear foci separate from their sites of synthesis and partially coincident with nuclear speckles. This labeling protocol should have many applications in RNA biology.

molecular biology↗

bioRxiv2018

Polypyrimidine Tract Binding Protein blocks microRNA-124 biogenesis to enforce its neuronal specific expression.

MicroRNA-124 is expressed in neurons, where it represses genes inhibitory for neuronal differentiation, including the RNA binding protein PTBP1. PTBP1 maintains non-neuronal splicing patterns of mRNAs that switch to neuronal isoforms upon neuronal differentiation. We find that pri-miR-124-1 is expressed in mouse embryonic stem cells (mESCs) where mature miR-124 is absent. PTBP1 binds to this precursor RNA upstream of the miRNA stem-loop to inhibit mature miR-124 expression in vivo, and DROSHA cleavage of pri-miR-124-1 in vitro. This new function for PTBP1 in repressing miR-124 biogenesis adds an additional regulatory loop to the already intricate interplay between these two molecules. Applying mathematical modeling to examine the dynamics of this regulation, we find that the pool of pri-miR-124 whose maturation is blocked by PTBP1 creates a robust and self-reinforcing transition in gene expression as PTBP1 is depleted during early neuronal differentiation. While interlocking regulatory loops are often modeled between miRNAs and transcriptional regulators, our results indicate that miRNA targeting of posttranscriptional regulators also reinforces developmental decisions. Notably, induction of neuronal differentiation observed upon PTBP1 knockdown likely results from direct de-repression of miR-124, in addition to indirect effects previously described.

molecular biology↗