Project description:BmN4 cells are cultured cells derived from Bombyx mori ovaries and widely used to study transposon silencing by PIWI-interacting RNAs (piRNAs). A high-accurate genome sequence of BmN4 cells is required to analyze the piRNA pathway using RNA-seq. The genome sequence of BmN4 cells was assembled using Pacific Biosciences (PacBio) HiFi and Oxford Nanopore technology Ultralong (ONT-UL) reads. Microscopic observation and image analysis showed that BmN4 cells were octoploid on average, and the number of chromosomes per cell was highly variable. We concluded the haplotype-resolved assembly of such a complex genome would be difficult; therefore, we assembled a consensus genome sequence. RNA-seq analysis of Siwi knockdown cells also revealed that Siwi-piRISC may target Countdown (Cd), an LTR retrotransposon. By comparing the consensus genome sequence with the reads, we identified differences between haplotypes, particulary structural variants, suggesting that some transposons, including Countdown, increased their copy number in BmN4 cells.
Project description:New tools for improved long-read transcript assembly and coalescence with its short-read counterpart are required. Using our short- and long-read measurements from different cell lines with spiked-in standards, we systematically compared key parameters and biases in the read alignment and assembly of transcripts. We report a cDNA synthesis artifact in long-read datasets that impacts the identity and quantitation of assembled transcripts. We developed a computational pipeline to strand long-read cDNA libraries that markedly improves assembly of transcripts from long-reads. Incorporating stranded long-reads in a new hybrid assembly approach, we demonstrate its efficacy for improved characterization of challenging lncRNA transcripts. Our workflow can be applied to a wide range of transcriptomics datasets for superior demarcation of transcript ends and refined isoform structure, which can enable better differential gene expression analyses and molecular manipulations of transcripts.