Kirsten A. Reimer

Bio: Kirsten A. Reimer is an academic researcher from Yale University. The author has contributed to research in topics: RNA splicing & Intron. The author has an hindex of 4, co-authored 5 publications receiving 46 citations.

Co-transcriptional splicing regulates 3' end cleavage during mammalian erythropoiesis

Abstract: Pre-mRNA processing steps are tightly coordinated with transcription in many organisms. To determine how co-transcriptional splicing is integrated with transcription elongation and 3’ end formation in mammalian cells, we performed long-read sequencing of individual nascent RNAs and PRO-seq during mouse erythropoiesis. Splicing was not accompanied by transcriptional pausing and was detected when RNA polymerase II (Pol II) was within 75 – 300 nucleotides of 3’ splice sites (3’SSs), often during transcription of the downstream exon. Interestingly, several hundred introns displayed abundant splicing intermediates, suggesting that splicing delays can take place between the two catalytic steps. Overall, splicing efficiencies were correlated among introns within the same transcript, and intron retention was associated with inefficient 3’ end cleavage. Remarkably, a thalassemia patient-derived mutation introducing a cryptic 3’SS improves both splicing and 3’ end cleavage of individual β-globin transcripts, demonstrating functional coupling between the two co-transcriptional processes as a determinant of productive gene output.

Rapid and Efficient Co-Transcriptional Splicing Enhances Mammalian Gene Expression

Abstract: Pre-mRNA splicing is tightly coordinated with transcription in yeasts, and introns can be removed soon after they emerge from RNA polymerase II (Pol II). To determine if splicing is similarly rapid and efficient in mammalian cells, we performed long read sequencing of nascent RNA during mouse erythropoiesis. Remarkably, 50% of splicing occurred while Pol II was within 150 nucleotides of 3′ splice sites. PRO-seq revealed that Pol II does not pause around splice sites, confirming that mammalian and yeast spliceosomes can act equally rapidly. Two exceptions were observed. First, several hundred introns displayed abundant splicing intermediates, suggesting that the spliceosome can stall after the first catalytic step. Second, some genes – notably globins – displayed poor splicing coupled to readthrough transcription. Remarkably, a patient-derived mutation in β-globin that causes thalassemia improves splicing efficiency and proper termination, revealing co-transcriptional splicing efficiency is a determinant of productive gene output.

Blood Relatives: Splicing Mechanisms underlying Erythropoiesis in Health and Disease.

Abstract: During erythropoiesis, hematopoietic stem and progenitor cells transition to erythroblasts en route to terminal differentiation into enucleated red blood cells. Transcriptome-wide changes underlie distinct morphological and functional characteristics at each cell division during this process. Many studies of gene expression have historically been carried out in erythroblasts, and the biogenesis of β-globin mRNA—the most highly expressed transcript in erythroblasts—was the focus of many seminal studies on the mechanisms of pre-mRNA splicing. We now understand that pre-mRNA splicing plays an important role in shaping the transcriptome of developing erythroblasts. Recent advances have provided insight into the role of alternative splicing and intron retention as important regulatory mechanisms of erythropoiesis. However, dysregulation of splicing during erythropoiesis is also a cause of several hematological diseases, including β-thalassemia and myelodysplastic syndromes. With a growing understanding of the role that splicing plays in these diseases, we are well poised to develop gene-editing treatments. In this review, we focus on changes in the developing erythroblast transcriptome caused by alternative splicing, the molecular basis of splicing-related blood diseases, and therapeutic advances in disease treatment using CRISPR/Cas9 gene editing.

Preparation of Mammalian Nascent RNA for Long Read Sequencing

Abstract: Long read sequencing technologies now allow high-quality sequencing of RNAs (or their cDNAs) that are hundreds to thousands of nucleotides long. Long read sequences of nascent RNA provide single-nucleotide-resolution information about co-transcriptional RNA processing events-e.g., splicing, folding, and base modifications. Here, we describe how to isolate nascent RNA from mammalian cells through subcellular fractionation of chromatin-associated RNA, as well as how to deplete poly(A)+ RNA and rRNA, and, finally, how to generate a full-length cDNA library for use on long read sequencing platforms. This approach allows for an understanding of coordinated splicing status across multi-intron transcripts by revealing patterns of splicing or other RNA processing events that cannot be gained from traditional short read RNA sequencing. © 2020 Wiley Periodicals LLC. Basic Protocol 1: Subcellular fractionation Basic Protocol 2: Nascent RNA isolation and adapter ligation Basic Protocol 3: cDNA amplicon preparation.

The complex genetic landscape of familial MDS and AML reveals pathogenic germline variants

Abstract: The inclusion of familial myeloid malignancies as a separate disease entity in the revised WHO classification has renewed efforts to improve the recognition and management of this group of at risk individuals. Here we report a cohort of 86 acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS) families with 49 harboring germline variants in 16 previously defined loci (57%). Whole exome sequencing in a further 37 uncharacterized families (43%) allowed us to rationalize 65 new candidate loci, including genes mutated in rare hematological syndromes (ADA, GP6, IL17RA, PRF1 and SEC23B), reported in prior MDS/AML or inherited bone marrow failure series (DNAH9, NAPRT1 and SH2B3) or variants at novel loci (DHX34) that appear specific to inherited forms of myeloid malignancies. Altogether, our series of MDS/AML families offer novel insights into the etiology of myeloid malignancies and provide a framework to prioritize variants for inclusion into routine diagnostics and patient management. Familial myeloid malignancies have recently been classified as separate disease entities. Here, using whole-exome sequencing of affected pedigrees - the authors highlight genetic variants associated with these conditions.

Co-transcriptional splicing regulates 3' end cleavage during mammalian erythropoiesis

Abstract: Pre-mRNA processing steps are tightly coordinated with transcription in many organisms. To determine how co-transcriptional splicing is integrated with transcription elongation and 3’ end formation in mammalian cells, we performed long-read sequencing of individual nascent RNAs and PRO-seq during mouse erythropoiesis. Splicing was not accompanied by transcriptional pausing and was detected when RNA polymerase II (Pol II) was within 75 – 300 nucleotides of 3’ splice sites (3’SSs), often during transcription of the downstream exon. Interestingly, several hundred introns displayed abundant splicing intermediates, suggesting that splicing delays can take place between the two catalytic steps. Overall, splicing efficiencies were correlated among introns within the same transcript, and intron retention was associated with inefficient 3’ end cleavage. Remarkably, a thalassemia patient-derived mutation introducing a cryptic 3’SS improves both splicing and 3’ end cleavage of individual β-globin transcripts, demonstrating functional coupling between the two co-transcriptional processes as a determinant of productive gene output.