Biology subjects

Pohjoismaki, J. L. O.

Publications and source records attributed to Pohjoismaki, J. L. O..

4 recordsLinked to original sources

bioRxiv2024

Chromosome-level reference genome assembly for the mountain hare (Lepus timidus)

We present here a high-quality genome assembly of a male mountain hare (Lepus timidus Linnaeus), from Ilomantsi, Eastern Finland, utilizing an isolated fibroblast cell line as the source for high quality DNA and RNA. Following the previously published brown hare reference genome assembly, the mountain hare is the second Finnish pilot species for the European Reference Genome Atlas (ERGA) initiative, a collaborative effort to generate reference genomes for European biodiversity. The genome was assembled using 21x PacBio HiFi sequencing data and scaffolded using the Hi-C chromosome structure capture approach. After manual curation, the primary assembly length was 2,695,305,354 bp with N50 125,755,317 bp. The largest scaffold was 181 Mbp and the scaffold N50 127 Mbp, contributing to a primary assembly consisting of 85 scaffolds and an alternate assembly with 109 scaffolds. The scaffolds include 23 autosomes, numbered according to their size, as well as X and Y chromosomes, matching the known karyotype. Telomeric regions were present on at least one end of 19 of the chromosomes. The genome has a high degree of completeness based on the BUSCO score (mammalia_odb10 database), Complete: 95.1 % [Single copy: 92.3 %, Duplicated: 2.7 %], Fragmented 0.8 %, and Missing 4.1 %. The mitochondrial genome of the cell line was sequenced and assembled separately. The assembly meets the Earth BioGenome Project criteria for a reference-standard genome assembly. Compared to the previous pseudo-reference genome assembly of L. timidus ssp. hibernicus Bell, assembled using the rabbit genome, this new reference genome represents the nominate subspecies and the species-specific chromosomal conformation. The published genome assembly will provide a solid foundation for future genomic research on Lagomorpha, including the insights into the genomic basis of adaptations to snowy and cold environments. Furthermore, it opens opportunities for experimental analysis of mountain hare gene functions.

genomics↗

bioRxiv2024

A small molecule inhibitor Mirin prevents TOP3A-dependent mtDNA breakage and segregation

Mirin, the chemical inhibitor of MRE11, has been recently reported to prevent immune response activation caused by mitochondrial DNA (mtDNA) breakage and release upon replication stalling. We show here that Mirin prevents mitochondrial replication fork breakage in mitochondrial 3-exonuclease MGME1 deficient cells and the resulting innate immune response induction, but that this occurs independently of MRE11. Furthermore, Mirin also caused alteration of mtDNA supercoiling and accumulation of hemicatenated replication termination intermediates, hallmarks of topoisomerase dysfunction, as well as alleviated topological changes induced by the overexpression of mitochondrial TOP3A, including TOP3A-dependent strand breakage at the non-coding region of mtDNA, potentially explaining its protective effect in the MGME1-knockout cells. Although Mirin does not inhibit TOP3A in vitro, our results demonstrate its MRE11-independent effects in cells and give insight into the mechanisms of mtDNA segregation, as well as the maintenance of genomic integrity in mitochondria. Significance StatementO_LIBroken mitochondrial DNA (mtDNA) in MGME1 knockout cells activates innate immune response, which is prevented by Mirin, a small molecule inhibitor of MRE11. C_LIO_LIMirin also interferes with mtDNA replication termination and segregation, suggesting that termination intermediates or paused forks are a major source of mtDNA breakage. C_LIO_LIWe show that these effects are likely dependent on topoisomerase 3A (TOP3A) -related processes in mitochondria, questioning the Mirin target also in the nucleus. C_LI

molecular biology↗

bioRxiv2024

Species-specific variation in mitochondrial genome tandem repeat polymorphisms in hares (Lepus spp., Lagomorpha, Leporidae) provides insight into their evolution

The non-coding regions of the mitochondrial DNAs (mtDNAs) of hares, rabbits, and pika (Lagomorpha) contain short ([~]20 bp) and long (130-160 bp) tandem repeats, absent in related mammalian orders. In the presented study, we provide functional annotation for mountain hare (Lepus timidus) and brown hare (L. europaeus) mtDNA non-coding regions, together with a species- and population-level analysis of tandem repeat variation. Mountain hare short tandem repeats (SRs) as well as other analyzed hare species consist of two conserved 10 bp motifs, with only brown hares exhibiting a single, more variable motif. Long tandem repeats (LRs) also differ in sequence and copy number between species. Mountain hares have four to seven LRs, median value five, while brown hares exhibit five to nine LRs, median value six. Interestingly, introgressed mountain hare mtDNA in brown hares obtained an intermediate LR length distribution, with median copy number being the same as with conspecific brown hare mtDNA. In contrast, transfer of brown hare mtDNA into cultured mtDNA-less mountain hare cells maintained the original LR number, whereas the reciprocal transfer caused copy number instability, suggesting that cellular environment rather than the nuclear genomic background plays a role in the LR maintenance. Due to their dynamic nature and separation from other known conserved sequence elements on the non-coding region of hare mitochondrial genomes, the tandem repeat elements are unlikely to have regulatory roles but are likely to represent selfish genetic elements.

genetics↗

bioRxiv2023

High quality genome of the Mountain hare (Lepus timidus) with new chromosome level scaffolding

We present here a high-quality genome assembly of the brown hare (Lepus europaeus Pallas), based on a fibroblast cell line of a male specimen from Liperi, Eastern Finland. This brown hare genome represents the first Finnish contribution to the European Reference Genome Atlas pilot effort to generate reference genomes for European biodiversity. The genome was assembled using 25X PacBio HiFi sequencing data and scaffolded utilizing a Hi-C chromosome structure capture approach. After manual curation, the assembled genome length was 2,930,972,003 bp with N50 scaffold of 125.8 Mb. 93.16% of the assembly could be assigned to 25 identified chromosomes (23 autosomes plus X and Y), matching the published karyotype. The chromosomes were numbered according to size. The genome has a high degree of completeness based on the BUSCO score (mammalia_odb10 database), Complete: 96.1% [Single copy: 93.1%, Duplicated: 3.0%], Fragmented 0.8%, and Missing 2.9%. The mitochondrial genome of the cell line was sequenced and assembled separately. The final annotated genome has 30,833 genes of which 21,467 code for a polypeptide. The brown hare genome is particularly interesting as this species readily hybridizes with the mountain hare (Lepus timidus L.) at the species contact zone in northern Eurasia, producing fertile offspring and resulting in gene flow between the two species. In addition to providing a useful comparison for population studies, the genome can offer insight into the chromosomal evolution among Glires in general and Lagomorpha in particular. The chromosomal assembly of the genome also demonstrates that the cell line has not acquired karyotypic changes during culture.

genomics↗