The genome of an apodid holothuroid (Chiridota heheva) provides insights into its adaptation to a deep-sea reducing environment

Sea cucumbers: an emerging system in evo-devo

A challenge for evolutionary developmental (evo-devo) biology is to expand the breadth of research organisms used to investigate how animal diversity has evolved through changes in embryonic development. New experimental systems should couple a relevant phylogenetic position with available molecular tools and genomic resources. As a phylum of the sister group to chordates, echinoderms extensively contributed to our knowledge of embryonic patterning, organ development and cell-type evolution. Echinoderms display a variety of larval forms with diverse shapes, making them a suitable group to compare the evolution of embryonic developmental strategies. However, because of the laboratory accessibility and the already available techniques, most studies focus on sea urchins and sea stars mainly. As a comparative approach, the field would benefit from including information on other members of this group, like the sea cucumbers (holothuroids), for which little is known on the molecular basis of their development. Here, we review the spawning and culture methods, the available morphological and molecular information, and the current state of genomic and transcriptomic resources on sea cucumbers. With the goal of making this system accessible to the broader community, we discuss how sea cucumber embryos and larvae can be a powerful system to address the open questions in evo-devo, including understanding the origins of bilaterian structures.

A high-quality chromosomal genome assembly of the sea cucumber Chiridota heheva and its hydrothermal adaptation

BACKGROUND

Chiridota heheva is a cosmopolitan holothurian well adapted to diverse deep-sea ecosystems, especially chemosynthetic environments. Besides high hydrostatic pressure and limited light, high concentrations of metal ions also represent harsh conditions in hydrothermal environments. Few holothurian species can live in such extreme conditions. Therefore, it is valuable to elucidate the adaptive genetic mechanisms of C. heheva in hydrothermal environments.

FINDINGS

Herein, we report a high-quality reference genome assembly of C. heheva from the Kairei vent, which is the first chromosome-level genome of Apodida. The chromosome-level genome size was 1.43 Gb, with a scaffold N50 of 53.24 Mb and BUSCO completeness score of 94.5%. Contig sequences were clustered, ordered, and assembled into 19 natural chromosomes. Comparative genome analysis found that the expanded gene families and positively selected genes of C. heheva were involved in the DNA damage repair process. The expanded gene families and the unique genes contributed to maintaining iron homeostasis in an iron-enriched environment. The positively selected gene RFC2 with 10 positively selected sites played an essential role in DNA repair under extreme environments.

CONCLUSIONS

This first chromosome-level genome assembly of C. heheva reveals the hydrothermal adaptation of holothurians. As the first chromosome-level genome of order Apodida, this genome will provide the resource for investigating the evolution of class Holothuroidea.

Comparative Analysis of Bivalve and Sea Urchin Genetics and Development: Investigating the Dichotomy in Bilateria

This comprehensive review presents a comparative analysis of early embryogenesis in Protostomia and Deuterostomia, the first of which exhibit a mosaic pattern of development, where cells are fated deterministically, while Deuterostomia display a regulatory pattern of development, where the fate of cells is indeterminate. Despite these fundamental differences, there are common transcriptional mechanisms that underline their evolutionary linkages, particularly in the field of functional genomics. By elucidating both conserved and unique regulatory strategies, this review provides essential insights into the comparative embryology and developmental dynamics of these groups. The objective of this review is to clarify the shared and distinctive characteristics of transcriptional regulatory mechanisms. This will contribute to the extensive areas of functional genomics, evolutionary biology and developmental biology, and possibly lay the foundation for future research and discussion on this seminal topic.

The First Genome Survey of the Snail Provanna glabra Inhabiting Deep-Sea Hydrothermal Vents

The snail P. glabra is an endemic species in deep-sea chemosynthetic ecosystems of the Northwest Pacific Ocean. To obtain more genetic information on this species and provide the basis for subsequent whole-genome map construction, a genome survey was performed on this snail from the hydrothermal vent of Okinawa Trough. The genomic size of P. glabra was estimated to be 1.44 Gb, with a heterozygosity of 1.91% and a repeated sequence content of 69.80%. Based on the sequencing data, a draft genome of 1.32 Gb was assembled. Transposal elements (TEs) accounted for 40.17% of the entire genome, with DNA transposons taking the highest proportion. It was found that most TEs were inserted in the genome recently. In the simple sequence repeats, the dinucleotide motif was the most enriched microsatellite type, accounting for 53% of microsatellites. A complete mitochondrial genome of P. glabra with a total length of 16,268 bp was assembled from the sequencing data. After comparison with the published mitochondrial genome of Provanna sp. from a methane seep, 331 potential single nucleotide polymorphism (SNP) sites were identified in protein-coding genes (PCGs). Except for the cox1 gene, nad2, nad4, nad5, and cob genes are expected to be candidate markers for population genetic and phylogenetic studies of P. glabra and other deep-sea snails. Compared with shallow-water species, three mitochondrial genes of deep-sea gastropods exhibited a higher evolutionary rate, indicating strong selection operating on mitochondria of deep-sea species. This study provides insights into the genome characteristics of P. glabra and supplies genomic resources for further studies on the adaptive evolution of the snail in extreme deep-sea chemosynthetic environments.

A high-quality chromosome-level genome assembly of Pelteobagrus vachelli provides insights into its environmental adaptation and population history

Pelteobagrus vachelli is a freshwater fish with high economic value, but the lack of genome resources has severely restricted its industrial development and population conservation. Here, we constructed the first chromosome-level genome assembly of P. vachelli with a total length of approximately 662.13 Mb and a contig N50 was 14.02 Mb, and scaffolds covering 99.79% of the assembly were anchored to 26 chromosomes. Combining the comparative genome results and transcriptome data under environmental stress (high temperature, hypoxia and Edwardsiella. ictaluri infection), the MAPK signaling pathway, PI3K-Akt signaling pathway and apelin signaling pathway play an important role in environmental adaptation of P. vachelli, and these pathways were interconnected by the ErbB family and involved in cell proliferation, differentiation and apoptosis. Population evolution analysis showed that artificial interventions have affected wild populations of P. vachelli. This study provides a useful genomic information for the genetic breeding of P. vachelli, as well as references for further studies on fish biology and evolution.