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Abstract Objective Global climate change has resulted in the decline of health and condition of various coral reefs worldwide. Here, we describe expression profiles of Acropora muricata collected during opposing seasons in Otsuki, Kochi, Japan to define the capacity of corals to cope with changing environmental conditions. Coral communities in Otsuki experience large temperature fluctuations between the winter (~ 16 °C) and summer (~ 27 °C). Results Coral nubbins that were collected in the summer showed no change in photochemical efficiency when exposed to thermal or cold stress, while winter samples showed a decrease in photochemical health when subjected to thermal stress. Under cold stress, corals that were collected in the summer showed an up-regulation of actin-related protein and serine/threonine protein kinase, while corals collected during the winter did not show any cellular stress. On the other hand, under thermal stress, the most notable change was the up-regulation of phosphoenolpyruvate carboxykinase in corals that were collected during the winter season. Our observations in the differential genes expressed under temperature-derived stress suggest that A. muricata from Kochi may maintain physiological resilience due to the frequently encountered environmental stress, and this may play a role in the coral’s thermal tolerance.

The diversity of sex determination systems in animals suggests that sex chromosomes evolve independently across different lineages. However, the present data on these systems is largely limited and represented mainly by bilaterian animals. Sex chromosomes and sex determination system based on cytogenetic evidence remain a mystery among non-bilaterians, the most basal animals. Here, we investigated the sex determination system of a non-bilaterian (Goniopora djiboutiensis) based on karyotypic analysis and identification of locus of dmrt1, a known master sex-determining gene in many animals. Results showed that among the three isolated dmrt genes, GddmrtC was sperm-linked. Fluorescence in situ hybridization revealed that 47% of the observed metaphase cells contained the GddmrtC locus on the shorter chromosome of the heteromorphic pair, whereas the other 53% contained no GddmrtC locus and pairing of the longer chromosome of the heteromorphic pair was observed. These findings provided the cytogenetic evidence for the existence of the Y sex chromosome in a non-bilaterian animal and supports male heterogamety as previously reported in other non-bilaterian species using RAD sequencing. The Y chromosome-specific GddmrtC sequence was most homologous to the vertebrate dmrt1, which is known for its role in male sex determination and differentiation. Our result on identification of putative sex chromosomes for G. djiboutiensis may contribute into understanding of the possible genetic sex determination systems in non-bilaterian animals. [ABSTRACT FROM AUTHOR]

Summary: Although sulfate ions are the main form of sulfur in the ocean, there is limited knowledge on their use by living organisms. Stable isotope labelling and NanoSIMS analysis were used in this study to clarify how sulfate, in seawater, is assimilated by corals and zooxanthellae at the cellular level. Aposymbiotic and symbiotic coral juveniles from the genus Acropora were incubated for 2 days in filtered seawater with 34S‐labelled sulfate. Further, the labelled corals were incubated for additional 2 days in natural seawater. Mapping of sulfur isotopes (34S/32S) showed that the 'hotspots' were enriched in 34S on a sub‐micro level and were heterogeneously distributed in the coral soft tissues. Specifically, 34S hotspots were found in both the symbiotic zooxanthellae and coral host tissues. In aposymbiotic corals, 34S was detected in the tissues, indicating that the host corals directly assimilated the sulfate ions without any aid from the zooxanthellae. Even after 2 days in normal seawater, the 34S label was clearly seen in both symbiotic and aposymbiotic corals, indicating that the assimilated sulfur was retained for at least 2 days. [ABSTRACT FROM AUTHOR]

Background: Corallium japonicum , a prized resource in Japan, plays a vital role in traditional arts and fishing industries. Because of diminished stock due to overexploitation, ongoing efforts are focused on restoration through transplantation. This study aimed to enhance our understanding of the reproductive biology of these valuable corals and find more efficient methods for sex determination, which may significantly contribute to conservation initiatives., Methods: We used 12 three-month aquarium reared C. japonicum colony fragments, conducted histological analysis for maturity and sex verification, and performed transcriptome analysis via de novo assembly and mapping using the C. rubrum transcriptome to explore gene expression differences between female and male C. japonicum ., Results: Our histological observations enabled sex identification in 33% of incompletely mature samples. However, the sex of the remaining 67% of samples, classified as immature, could not be identified. RNA-seq yielded approximately 21-31 million short reads from 12 samples. De novo assembly yielded 404,439 highly expressed transcripts. Among them, 855 showed significant differential expression, with 786 differentially expressed transcripts between females and males. Heatmap analysis highlighted 283 female-specific and 525 male-specific upregulated transcripts. Transcriptome assembly mapped to C. rubrum yielded 28,092 contigs, leading to the identification of 190 highly differentially expressed genes, with 113 upregulated exclusively in females and 70 upregulated exclusively in males. Blastp analysis provided putative protein annotations for 83 female and 72 male transcripts. Annotation analysis revealed that female biological processes were related to oocyte proliferation and reproduction, whereas those in males were associated with cell adhesion., Discussion: Transcriptome analysis revealed sex-specific gene upregulation in incompletely mature C. japonicum and shared transcripts with C. rubrum , providing insight into its gene expression patterns. This study highlights the importance of using both de novo and reference-based assembly methods. Functional enrichment analysis showed that females exhibited enrichment in cell proliferation and reproduction pathways, while males exhibited enrichment in cell adhesion pathways. To the best of our knowledge, this is the first report on the gene expressions of each sex during the spawning season. Our findings offer valuable insights into the physiological ecology of incompletely mature red Japanese precious corals and suggest a method for identifying sex using various genes expressed in female and male individuals. In the future, techniques such as transplantation, artificial fertilization, and larval rearing may involve sex determination methods based on differences in gene expression to help conserve precious coral resources and ecosystems., Competing Interests: The authors declare there are no competing interests., (©2024 Pepino et al.)

Since the Roman era, precious corals have been used to make ornaments worldwide, and their demand has recently increased. As a basic study for artificial cultivation, we transplanted Corallium japonicum fragments. In 2016 and 2017, 132 fragments approximately 3-5 cm in length were attached to small-sized artificial substratums using marine epoxy on land. These artificial substratums, acting as transplant substrates, were then transported and sunk to a depth approximately 100 m off the coast of Otsuki Town and Tosashimizu City, Kochi Prefecture, where precious corals once flourished. From six months to three years post-submersion, we successfully recovered the transplanted substrates and found a total of 107 fragments (81%). We confirmed that 106 of these fragments were alive 177 to 936 days after transplantation. Although we could not measure growth rates due to the initial damage caused by the transplantation, we observed growth in coenenchyme tissues, new polyps and new branches in the 104 surviving fragments. This result suggests there is great potential to artificially multiply precious corals, which could aid in the development of a sustainable precious coral industry.

We performed conventional and molecular cytogenetic studies on the Favitespentagona Esper, 1795, a scleractinian coral mostly found along the west coast of Japan. Karyotype analysis of F.pentagona by G-banding revealed a karyogram containing a homogenously staining region (HSR) on chromosome 10 in more than 50% of the examined metaphase spreads. This HSR consisted of sequences from 18S ribosomal RNA (rRNA) genes, as demonstrated by fluorescence in situ hybridization (FISH) and DNA sequencing. We highlighted the development of four chromosomal FISH markers from repetitive genes such as U2 small nuclear RNA linked to 5S rRNA sequence (U2 snRNA-5S), 18S rRNA, histone H3, and uncharacterized gene FP-9X. The chromosomal locations of the U2 snRNA-5S and 18S RNA were on the terminal end of long arm of chromosomes 2 and 10, respectively, while the histone H3 and the uncharacterized gene were located near the centromeres of chromosomes 1 and 9, respectively. These FISH markers will improve the karyotyping of F.pentagona from mitotic preparations which helps in widening our understanding of coral genetic structure and chromosome organization. In addition, these improvements in karyotyping will provide the basis in constructing of chromosome-level genome assembly for F.pentagona ., (Rei Kawakami, Takahiro Taguchi, Joshua Vacarizas, Masumi Ito, Takuma Mezaki, Akira Tominaga, Satoshi Kubota.)