Biology subjects

Guiglielmoni, N.

Publications and source records attributed to Guiglielmoni, N..

25 records · Page 2Linked to original sources

bioRxiv2022

Chromosome-level genome assembly and annotation of two lineages of the ant Cataglyphis hispanica: steppingstones towards genomic studies of hybridogenesis and thermal adaptation in desert ants

AO_SCPLOWBSTRACTC_SCPLOWCataglyphis are thermophilic ants that forage during the day when temperatures are highest and sometimes close to their critical thermal limit. Several Cataglyphis species have evolved unusual reproductive systems such as facultative queen parthenogenesis or social hybridogenesis, which have not yet been investigated in detail at the molecular level. We generated high-quality genome assemblies for two hybridogenetic lineages of the Iberian ant Cataglyphis hispanica using long-read Nanopore sequencing and exploited chromosome conformation capture (3C) sequencing to assemble contigs into 26 and 27 chromosomes, respectively. Further karyotype analyses confirm this difference in chromosome numbers between lineages; however, they also suggest it may not be fixed among lineages. We obtained transcriptomic data to assist gene annotation and built custom repeat libraries for each of the two assemblies. Comparative analyses with 19 other published ant genomes were also conducted. These new genomic resources pave the way for exploring the genetic mechanisms underlying the remarkable thermal adaptation and the molecular mechanisms associated with transitions between different genetic systems characteristic of the ant genus Cataglyphis.

genomics↗

bioRxiv2021

GraphUnzip: unzipping assembly graphs with long reads and Hi-C

Long reads and Hi-C have revolutionized the field of genome assembly as they have made highly continuous assemblies accessible for challenging genomes. As haploid chromosome-level assemblies are now commonly achieved for all types of organisms, phasing assemblies has become the new frontier for genome reconstruction. Several tools have already been released using long reads and/or Hi-C to phase assemblies, but they all start from a linear sequence, and are ill-suited for non-model organisms with high levels of heterozygosity. We present GraphUnzip, a fast, memory-efficient and accurate tool to unzip assembly graphs into their constituent haplotypes using long reads and/or Hi-C data. As GraphUnzip only connects sequences in the assembly graph that already had a potential link based on overlaps, it yields high-quality gap-less supercontigs. To demonstrate the efficiency of GraphUnzip, we tested it on a simulated diploid Escherichia coli genome, and on two real datasets for the genomes of the rotifer Adineta vaga and the potato Solanum tuberosum. In all cases, GraphUnzip yielded highly continuous phased assemblies.

bioinformatics↗

bioRxiv2020

The de novo genome of the "Spanish" slug Arion vulgaris Moquin-Tandon, 1855 (Gastropoda: Panpulmonata): massive expansion of transposable elements in a major pest species

BackgroundThe "Spanish" slug, Arion vulgaris Moquin-Tandon, 1855, is considered to be among the 100 worst pest species in Europe. It is common and invasive to at least northern and eastern parts of Europe, probably benefitting from climate change and the modern human lifestyle. The origin and expansion of this species, the mechanisms behind its outstanding adaptive success and ability to outcompete other land slugs are worth to be explored on a genomic level. However, a high-quality chromosome-level genome is still lacking. FindingsThe final assembly of A. vulgaris was obtained by combining short reads, linked reads, Nanopore long reads, and Hi-C data. The genome assembly size is 1.54 Gb with a contig N50 length of 8.6 Mb. We found a recent expansion of transposable elements (TEs) which results in repetitive sequences accounting for more than 75% of the A. vulgaris genome, which is the highest among all known gastropod species. We identified 32,518 protein coding genes, and 2,763 species specific genes were functionally enriched in response to stimuli, nervous system and reproduction. With 1,237 single-copy orthologs from A. vulgaris and other related mollusks with whole-genome data available, we reconstructed the phylogenetic relationships of gastropods and estimated the divergence time of stylommatophoran land snails (Achatina) and Arion slugs at around 126 million years ago, and confirmed the whole genome duplication event shared by them. ConclusionsTo our knowledge, the A. vulgaris genome is the first land slug genome assembly published to date. The high-quality genomic data will provide valuable genetic resources for further phylogeographic studies of A. vulgaris origin and expansion, invasiveness, as well as molluscan aquatic-land transition and shell formation.

genomics↗

bioRxiv2020

Homologous chromosomes in asexual rotifer Adineta vaga suggest automixis

The several hundreds of species of bdelloid rotifers are notorious because they represent an ancient clade comprising only asexual lineages1. Moreover, most bdelloid species have the ability to withstand complete desiccation and high doses of ionizing radiation, being able to repair their DNA after massive genome breakage2. To better understand the impact of long-term asexuality and DNA breakage on genome evolution, a telomere-to-tolemere reference genome assembly of a bdelloid species is critical3, 4. Here we present the first, high quality chromosome-scale genome assembly for the bdelloid A. vaga validated using three complementary assembly procedures combined with chromosome conformation capture (Hi-C) data. The different assemblies reveal the same genome architecture and using fluorescent in situ hybridization (FISH), we demonstrate that the A. vaga genome is composed of six pairs of homologous chromosomes, compatible with meiosis. Moreover, the synteny between homoeologous (or ohnologous) chromosomes is also preserved, confirming their paleotetraploidy. The diploid genome structure of A. vaga and the presence of very long homozygous tracts show that recombination between homologous chromosomes occurs in this ancient asexual scandal, either during DSB repair or during meiotic pairing. These homozygosity tracts are mainly observed towards the chromosome ends in the clonal A. vaga suggesting signatures of a parthenogenetic mode of reproduction equivalent to central fusion automixis, in which homologous chromosomes are not segregated during the meiotic division.

evolutionary biology↗

bioRxiv2020

Overcoming uncollapsed haplotypes in long-read assemblies of non-model organisms

BackgroundThird-generation sequencing, also called long-read sequencing, is revolutionizing genome assembly: as PacBio and Nanopore technologies become more accessible in technicity and in cost, long-read assemblers flourish and are starting to deliver chromosome-level assemblies. However, these long reads are also error-prone, making the generation of a haploid reference out of a diploid genome a difficult enterprise. Although failure to properly collapse haplotypes results in fragmented and/or structurally incorrect assemblies and wreaks havoc on orthology inference pipelines, this serious issue is rarely acknowledged and dealt with in genomic projects, and an independent, comparative benchmark of the capacity of assemblers and post-processing tools to properly collapse or purge haplotypes is still lacking. ResultsTo fill this gap, we tested different assembly strategies on the genome of the rotifer Adineta vaga, a non-model organism for which high coverages of both PacBio and Nanopore reads were available. The assemblers we tested (Canu, Flye, NextDenovo, Ra, Raven, Shasta and wtdbg2) exhibited strikingly different behaviors when dealing with highly heterozygous regions, resulting in variable amounts of uncollapsed haplotypes. Filtering out shorter reads generally improved haploid assemblies, and we also benchmarked three post-processing tools aimed at detecting and purging uncollapsed haplotypes in long-read assemblies: HaploMerger2, purge_haplotigs and purge_dups. ConclusionsTesting these strategies separately and in combination revealed several approaches able to generate haploid assemblies with genome sizes, coverage distributions, and completeness close to expectations.

genomics↗

bioRxiv2020

Chromosight: A computer vision program for pattern detection in chromosome contact maps

Chromosomes of all species studied so far display a variety of higher order organizational features such as domains or loops often associated to biological functions and visible on Hi-C contact maps. We developed Chromosight, an algorithm inspired from computer vision that can detect patterns in Hi-C maps. Chromosight has greater sensitivity than existing methods, while being faster and applicable to any type of genomes, including bacteria, viruses, yeasts and mammals. Code and documentation: https://github.com/koszullab/chromosight

bioinformatics↗

bioRxiv2019

Chromosome-level quality scaffolding of brown algal genomes using InstaGRAAL, a proximity ligation-based scaffolder

Hi-C has become a popular technique in recent genome assembly projects. Hi-C exploits contact frequencies between pairs of loci to bridge and order contigs in draft genomes, resulting in chromosome-level assemblies. However, application of this approach is currently hampered by a lack of robust programs that are capable of effectively treating this type of data, particularly open source programs. We developed instaGRAAL, a complete overhaul of the GRAAL program, which has adapted the latter to allow efficient assembly of large genomes. Both GRAAL, and instaGRAAL use a Markov Chain Monte Carlo algorithm to perform Hi-C scaffolding, but instaGRAAL features a number of improvements including a modular polishing approach that optionally integrates independent data. To validate the program, we used it to generate chromosome-level assemblies for two brown algae, Desmarestia herbacea and the model Ectocarpus sp., and quantified improvements compared to the initial draft for the latter. Overall, instaGRAAL is a program able to generate, using default parameters with minimal human intervention, near-complete assemblies.

genomics↗