Biology subjects

Sales-Lee, J.

Publications and source records attributed to Sales-Lee, J..

5 recordsLinked to original sources

bioRxiv2023

Functional Screening in human HSPCs identifies optimized protein-based enhancers of Homology Directed Repair

Homology Directed Repair (HDR) enables precise genome editing and holds great promise in the gene therapy field. However, the implementation of HDR-based therapies is hindered by limited efficiency in comparison to methods that exploit alternative DNA repair routes, such as Non-Homologous End Joining (NHEJ). In this study, we demonstrate the development of a functional, pooled screening platform utilizing an HDR-based readout to identify protein-based reagents that improve HDR outcomes in human hematopoietic stem and progenitor cells (HSPCs), a clinically relevant cell type for gene therapy. We leveraged this screening platform to explore sequence diversity at the binding interface of the NHEJ inhibitor i53 and its target, 53BP1, and we identified optimized i53 variants that enable new intermolecular bonds and robustly increase HDR. These variants specifically reduce insertion-deletion outcomes and also synergize with a DNAPK inhibitor to increase HDR rates. When applied at manufacturing scale, the incorporation of improved variants results in a significant increase in cells with at least one repaired allele and improved HDR in long-term HSPCs subpopulations, while not increasing off-target editing or gross chromosomal rearrangements. We anticipate the pooled screening platform will enable discovery of future gene editing reagents that improve HDR outcomes, such as the i53 variants reported here.

molecular biology↗

bioRxiv2021

Coupling of spliceosome complexity to intron diversity

We determined that over 40 spliceosomal proteins are conserved between many fungal species and humans but were lost during the evolution of S. cerevisiae, an intron-poor yeast with unusually rigid splicing signals. We analyzed null mutations in a subset of these factors, most of which had not been investigated previously, in the intron-rich yeast Cryptococcus neoformans. We found they govern splicing efficiency of introns with divergent spacing between intron elements. Importantly, most of these factors also suppress usage of weak nearby cryptic/alternative splice sites. Among these, orthologs of GPATCH1 and the helicase DHX35 display correlated functional signatures and copurify with each other as well as components of catalytically active spliceosomes, identifying a conserved G-patch/helicase pair that promotes splicing fidelity. We propose that a significant fraction of spliceosomal proteins in humans and most eukaryotes are involved in limiting splicing errors, potentially through kinetic proofreading mechanisms, thereby enabling greater intron diversity.

molecular biology↗

bioRxiv2019

Start codon context controls translation initiation in the fungal kingdom

Eukaryotic protein synthesis initiates at a start codon defined by an AUG and its surrounding Kozak sequence context, but studies of S. cerevisiae suggest this context is of little importance in fungi. We tested this concept in two pathogenic Cryptococcus species by genome-wide mapping of translation and of mRNA 5 and 3 ends. We observed that upstream open reading frames (uORFs) are a major contributor to translation repression, that uORF use depends on the Kozak sequence context of its start codon, and that uORFs with strong contexts promote nonsense-mediated mRNA decay. Numerous Cryptococcus mRNAs encode predicted dual-localized proteins, including many aminoacyl-tRNA synthetases, in which a leaky AUG start codon is followed by a strong Kozak context in-frame AUG, separated by mitochondrial-targeting sequence. Further analysis shows that such dual-localization is also predicted to be common in Neurospora crassa. Kozak-controlled regulation is correlated with insertions in translational initiation factors in fidelity-determining regions that contact the initiator tRNA. Thus, start codon context is a signal that programs the expression and structures of proteins in fungi.

genomics↗

bioRxiv2019

A non-Dicer RNase III and four other novel factors required for RNAi-mediated transposon suppression in the human pathogenic yeast C. neoformans

The human pathogenic yeast Cryptococcus neoformans silences transposable elements using endo-siRNAs and an Argonaute, Ago1. Endo-siRNAs production requires the RNA-dependent RNA polymerase, Rdp1, and two partially redundant Dicer enzymes, Dcr1 and Dcr2, but is independent of histone H3 lysine 9 methylation. We describe here an insertional mutagenesis screen for factors required to suppress the mobilization of the C. neoformans HARBINGER family DNA transposon HAR1. Validation experiments uncovered five novel genes (RDE1-5) required for HAR1 suppression and global production of suppressive endo-siRNAs. Loss of the RDE genes does not impact transcript levels, suggesting the endo-siRNAs do not act by impacting target transcript synthesis or turnover. RDE3 encodes a non-Dicer RNase III related to S. cerevisiae Rnt1, RDE4 encodes a predicted terminal nucleotidyltransferase, while RDE5 has no strongly predicted encoded domains. Affinity purification-mass spectrometry studies reveal that Rde3 and Rde5 are physically associated. RDE1 encodes a G-patch protein homologous to the S. cerevisiae Sqs1/Pfa1, a nucleolar protein that directly activates the essential helicase Prp43 during rRNA biogenesis. Rde1 copurifies Rde2, another novel protein obtained in the screen, as well as Ago1, a homolog of Prp43, and numerous predicted nucleolar proteins. We also describe the isolation of conditional alleles of PRP43, which are defective in RNAi. This work reveals unanticipated requirements for a non-Dicer RNase III and presumptive nucleolar factors for endo-siRNA biogenesis and transposon mobilization suppression in C. neoformans.

molecular biology↗

bioRxiv2017

Spliceosome profiling visualizes the operations of a dynamic RNP in vivo at nucleotide resolution

Tools to understand how the spliceosome functions in vivo have lagged behind advances in its structural biology. We describe methods to globally profile spliceosome-bound precursor, intermediates and products at nucleotide resolution. We apply these tools to three divergent yeast species that span 600 million years of evolution. The sensitivity of the approach enables detection of novel cases of non-canonical catalysis including interrupted, recursive and nested splicing. Employing statistical modeling to understand the quantitative relationships between RNA features and the data, we uncover independent roles for intron size, position and number in substrate progression through the two catalytic stages. These include species-specific inputs suggestive of spliceosome-transcriptome coevolution. Further investigations reveal ATP-dependent discard of numerous endogenous substrates at both the precursor and lariat-intermediate stages and connect discard to intron retention, a form of splicing regulation. Spliceosome profiling is a quantitative, generalizable global technology to investigate an RNP central to eukaryotic gene expression.\n\nHighlightsO_LIMeasurement of spliceosome-bound precursor and intermediate in three species\nC_LIO_LINon-canonical splicing events revealed\nC_LIO_LIStatistical modeling uncovers substrate features that predict catalytic efficiency\nC_LIO_LIDiscard of suboptimal substrates occurs in vivo and predicts intron-retained mRNAs\nC_LI

molecular biology↗