Biology subjects

Grethlein, M.

Publications and source records attributed to Grethlein, M..

4 recordsLinked to original sources

bioRxiv2026

Chromosome-level reference genome assembly of the Saimaa ringed seal (Pusa saimensis) - an ancient glacial relict landlocked pinniped

We present a high-quality chromosome-level reference genome for the Saimaa ringed seal (Pusa saimensis), an endangered freshwater pinniped endemic to Lake Saimaa, Finland. The assembly spans 2.353 Gb and comprises 15 autosomes together with the X and Y sex chromosomes. Using Oxford Nanopore Technologies (ONT) long-read sequencing and Hi-C scaffolding, we achieved a telomere-to-telomere assembly for all chromosomes, except the Y chromosome. Genome annotation identified approximately 21,800 protein-coding genes, consistent with other mammalian genomes. Assembly completeness was high, with BUSCO analysis recovering 99.6% of expected complete single-copy genes (98.2% single-copy and 1.3% duplicated). Comparative analyses revealed a highly conserved chromosomal architecture, with only minor syntenic differences relative to other pinniped chromosome-level assemblies. Previously described cytogenetic fusion events in Phocidae were confirmed (chromosomes 2 and 7). A translocation between chromosomes 6 and 7 distinguishes phocids from the otariids. In general, more distantly related taxa exhibit an increasing degree of intrachromosomal rearrangements. Notably, we identified a large intrachromosomal rearrangement on chromosome 2 that appears specific to the Saimaa ringed seal. Phylogenomic analysis based on 9,226 single-copy orthologues placed the Saimaa ringed seal as a sister lineage to the Baltic ringed seal (Pusa hispida botnica), while confirming also other established evolutionary relationships among pinnipeds. Comparative gene family analysis between the Saimaa ringed seal and the closely related grey seal (Halichoerus grypus) revealed lineage-specific differences driven by a limited number of gene families. In the Saimaa ringed seal, expansions were observed in ion transport, cytoskeleton, and regulatory genes, potentially reflecting adaptation to freshwater conditions. In contrast, the grey seal showed expansions in olfaction, immune-and spermatogenesis-associated gene families, including MAGE/MIA genes, consistent with differences in ecology and mating systems. This reference genome provides an important resource for studies of pinniped genome evolution, as well as conservation and population genomics of the Saimaa ringed seal, facilitating future work on genetic diversity, inbreeding, mutational load and adaptive potential in this highly endangered species.

genomics↗

bioRxiv2025

Near-chromosome-level genome assembly and transcriptome of the Ural owl, Strix uralensis PALLAS, 1771

The Ural owl (Strix uralensis) is a large member of the Strigidae family and inhabits Eurasian forests ranging from Germany to Japan. However, it faces increased range reduction, particularly at its southwestern distribution edges. Despite being considered "Least Concern" by the IUCN, local populations have become threatened in Central Europe due to severe habitat loss. Reintroduction programs aim to restore these populations by closing distribution gaps and facilitating natural recolonization of suitable habitats. To support these efforts, genomic resources have become an established tool to assess genetic diversity, geographic structure, and potential inbreeding, crucial for maintaining the genetic health and adaptability of newly established populations. Here, we present a de novo genome assembly and transcriptome of the Ural owl based on ONT long-reads, Omni-C Illumina short-reads, and RNASeq data. The final assembly has a total length of 1.26 Gb, of which 96.37 % are anchored into the 41 largest scaffolds. The contig and scaffold N50 values of 88.6 Mb and 21.7 Mb, respectively, a BUSCO/compleasm completeness of 97.5 %/99.65 % and k-mer completeness of 95.18 %, emphasize the high quality of this assembly. Furthermore, annotation of the assembly identified 17,650 genes and a repeat content of 12.48 %. This new highly contiguous and chromosome-scale assembly will greatly benefit Ural owl conservation management by informing reintroduction programs about the species genetic health and contributing a valuable resource to study genetic function in greater detail across the whole Strigidae family.

genomics↗

bioRxiv2024

Miniaturised laboratorial equipment as a solution to implement conservation genetics tools and education in West African countries with limited infrastructures: an application to the study of illegal wildlife trade in Guinea-Bissau

Illegal wildlife trade (IWT) is considered one of the largest global illegal industries that negatively impacts biodiversity and sustainable development worldwide. DNA barcoding coupled with high-throughput sequencing has been shown to be useful in identifying taxa affected by IWT and has been routinely used during the last decades. However, for countries lacking laboratory infrastructures and sequencing units or trained staff, the application of DNA barcoding tools in conservation actions and policies is limited and dependent on slow sample export processes and molecular analyses carried out abroad. Guinea-Bissau (GB) is located on the West-African coast and has one of the lowest human development indices worldwide, while being a biodiversity hotspot facing many conservation challenges due to illegal commercial hunting, and trade in bushmeat and live individuals. Here, we explore the potential of using inexpensive and portable miniaturised laboratory equipment (MLE) to i) identify species illegally traded in GB using DNA barcoding methods and ii) to improve molecular biology and conservation genetic education and training in GB. Our overarching aim is to raise awareness of the current gap between the need to apply conservation genetic technologies in GB and the inability to do so due to a lack of laboratory infrastructures, sequencing units and opportunities for molecular biology training. We show that MLE can be a solution to accelerate the use of DNA barcoding methods to understand IWT and to train students, technicians and staff from governmental agencies dedicated to investigating environmental crimes, ultimately advancing the discipline of conservation genetics in the country.

zoology↗

bioRxiv2020

Improving the chromosome-level genome assembly of the Siamese fighting fish (Betta splendens) in a university Master's course.

BackgroundEver decreasing costs along with advances in sequencing and library preparation technologies enable even small research groups to generate chromosome-level assemblies today. Here we report the generation of an improved chromosome-level assembly for the Siamese fighting fish (Betta splendens) that was carried out during a practical university Masters course. The Siamese fighting fish is a popular aquarium fish and an emerging model species for research on aggressive behaviour. We updated the current genome assembly by generating a new long-read nanopore-based assembly with subsequent scaffolding to chromosome-level using previously published HiC data. FindingsThe use of nanopore-based long-read data sequenced on a MinION platform (Oxford Nanopore Technologies) allowed us to generate a baseline assembly of only 1,276 contigs with a contig N50 of 2.1 Mbp, and a total length of 441 Mbp. Scaffolding using previously published HiC data resulted in 109 scaffolds with a scaffold N50 of 20.7 Mbp. More than 99% of the assembly is comprised in 21 scaffolds. The assembly showed the presence of 95.8% complete BUSCO genes from the Actinopterygii dataset indicating a high quality of the assembly. ConclusionWe present an improved full chromosome-level assembly of the Siamese fighting fish generated during a university Masters course. The use of ~35x long-read nanopore data drastically improved the baseline assembly in terms of continuity. We show that relatively in-expensive high-throughput sequencing technologies such as the long-read MinION sequencing platform can be used in educational settings allowing the students to gain practical skills in modern genomics and generate high quality results that benefit downstream research projects.

evolutionary biology↗