Biology subjects

Olson, P. D.

Publications and source records attributed to Olson, P. D..

3 recordsLinked to original sources

bioRxiv2023

Segmentation in tapeworms as a modified form of flatworm posterior regeneration involving Wnt and Hedgehog signalling

Tapeworms are parasitic flatworms that lack key features conventionally used to define the head-tail axis in free-living organisms, resulting in long standing questions regarding the true orientation of their main body axis. As adults, most tapeworms also exhibit a segmented body which has been considered an adaptation unique to the group. Anteroposterior (AP) patterning in free-living flatworms is controlled by {beta}-catenin-dependent Wnt signalling and positional control genes are expressed by their musculature in highly regionalised domains. Here we investigate the expression of Wnt and Hedgehog components during the strobilar phase of the tapeworm life cycle during which larval tissues are lost and replaced through the continuous production of new tissues. Results reveal previously unidentified centres of signalling associated with their neuromuscular system and show that segments are marked by secondary, AP axes in agreement with the polarity of the primary body axis. Neuromuscular expression and communication between Wnt and Hedgehog signalling is consistent with embryonic and regenerative growth in planarians and is a common mechanism for establishing AP-polarised boundaries in a diverse range of segmented animals. Taken together our results suggest that segmentation in tapeworms represents a modified form of posterior regeneration, a common feature among flatworms.

developmental biology↗

bioRxiv2023

Highly resolved genome assembly and comparative transcriptome profiling reveal genes related to developmental stages of the tapeworm Ligula intestinalis

Ligula intestinalis (Cestoda: Diphyllobothriidae) is an emerging model organism for studies on parasite population biology and host-parasite interactions. However, a well resolved genome and catalogue of its gene content has not been previously developed. Here, we present the first genome assembly of L. intestinalis, based on Oxford Nanopore Technologies, Illumina and Omni-C sequencing methodologies. We use transcriptome profiling to compare plerocercoid larvae and adult worms and identify differentially expressed genes associated with these life stages. The genome assembly is 775.5 Mbp in size, with scaffold N50 value of 118 Mbp and encodes 27,256 predicted protein-coding sequences. Over 60% of the genome consists of repetitive sequences. Synteny analyses showed that the 10 largest scaffolds representing 75% of the genome display high correspondence to full chromosomes of cyclophyllidean tapeworms. Mapping RNA-seq data to the new reference genome we identified 3,922 differentially expressed genes in adults compared to plerocercoids. Gene Ontology analyses revealed overrepresented genes involved in reproductive development of the adult stage (e.g. sperm production) and significantly enriched DEGs associated with immune evasion of plerocercoids in their fish host. This study provides the first insights into the molecular biology of L. intestinalis and provides the most highly contiguous assembly to date of a diphyllobothriid tapeworm useful for population and comparative genomic investigations of parasitic flatworms.

genomics↗

bioRxiv2020

Complete representation of a tapeworm genome reveals chromosomes capped by centromeres, necessitating a dual role in segregation and protection

BackgroundChromosome-level assemblies are indispensable for accurate gene prediction, synteny assessment and understanding higher-order genome architecture. Reference and draft genomes of key helminth species have been published but little is yet known about the biology of their chromosomes. Here we present the complete genome of the tapeworm Hymenolepis microstoma, providing a reference-quality, end-to-end assembly that represents the first fully assembled genome of a spiralian/lophotrochozoan, revealing new insights into chromosome evolution. ResultsLong-read sequencing and optical mapping data were added to previous short-read data enabling complete re-assembly into six chromosomes, consistent with karyology. Small genome size (169 Mb) and lack of haploid variation (1 SNP/3.2 Mb) contributed to exceptionally high contiguity with only 85 gaps remaining in regions of low complexity sequence. Resolution of repeat regions reveals novel gene expansions, micro-exon genes, and spliced leader transsplicing, and illuminates the landscape of transposable elements, explaining observed length differences in sister chromatids. Syntenic comparison with other parasitic flatworms shows conserved ancestral linkage groups indicating that the H. microstoma karyotype evolved through fusion events. Strikingly, the assembly reveals that the chromosomes terminate in centromeric arrays, indicating that these motifs play a role not only in segregation, but also in protecting the linear integrity and full lengths of chromosomes. ConclusionsDespite strong conservation of canonical telomeres, our results show that they can be substituted by more complex, species-specific sequences, as represented by centromeres. The assembly provides a robust platform for investigations that require complete genome representation.

genomics↗