Biology subjects

Ashey, J.

Publications and source records attributed to Ashey, J..

4 recordsLinked to original sources

bioRxiv2024

Coral larvae employ nitrogen sequestration mechanisms to stabilize carbon provisioning from algal symbionts under increased temperature

Rising sea surface temperatures are increasingly causing breakdown in the nutritional relationship between corals and algal endosymbionts (Symbiodiniaceae), threatening the basis of coral reef ecosystems and highlighting the critical role of coral reproduction in reef maintenance. The effects of thermal stress on metabolic exchange (i.e., transfer of fixed carbon photosynthates from symbiont to host) during sensitive early life stages, however, remains understudied. We exposed symbiotic Montipora capitata coral larvae in Hawaii to high temperature (+2.5{degrees}C for 3 days), assessed rates of photosynthesis and respiration, and used stable isotope tracing (4mM 13C sodium bicarbonate; 4.5 h) to quantify metabolite exchange. While larvae did not show any signs of bleaching and did not experience declines in survival and settlement, metabolic depression was significant under high temperature, indicated by a 19% reduction in respiration rates, but with no change in photosynthesis. Larvae exposed to high temperature showed evidence for maintained translocation of a major photosynthate, glucose, from the symbiont, but there was reduced metabolism of glucose through central carbon metabolism (i.e., glycolysis). The larval host invested in nitrogen cycling by increasing ammonium assimilation, urea metabolism, and sequestration of nitrogen into dipeptides, a mechanism that may support the maintenance of glucose translocation under thermal stress. Host nitrogen assimilation via dipeptide synthesis appears to be used for nitrogen limitation to the Symbiodiniaceae, with the outcome of reduced symbiont population growth and retention of fixed carbon, effectively simulating photosynthate translocation to the host. Collectively, our findings indicate that although these larvae are susceptible to metabolic stress under high temperature, they can combat bleaching by diverting energy to nitrogen assimilation to maintain symbiont population density, photosynthesis, and carbon translocation.

cell biology↗

bioRxiv2024

DNA methylation modulates transcriptional noise in response to elevated pCO2 in the eastern oyster (Crassostrea virginica)

Ocean acidification significantly affects marine calcifiers like oysters, warranting the study of molecular mechanisms like DNA methylation that contribute to adaptive plasticity in response to environmental change. However, a consensus has not been reached on the extent to which methylation modules gene expression, and in turn plasticity, in marine invertebrates. In this study, we investigated the impact of pCO2 on gene expression and DNA methylation in the eastern oyster, Crassostrea virginica. After a 30-day exposure to control (572 ppm) or elevated pCO2 (2,827 ppm), whole genome bisulfite sequencing (WGBS) and RNA-Seq data were generated from adult female gonad tissue and male sperm samples. Although differentially methylated loci (DML) were identified in females (89) and males (2,916), there were no differentially expressed genes, and only one differentially expressed transcript in females. However, gene body methylation impacted other forms of gene activity in sperm, such as the maximum number of transcripts expressed per gene and changes in the predominant transcript expressed. Elevated pCO2 exposure increased gene expression variability (transcriptional noise) in males but decreased noise in females, suggesting a sex-specific role of methylation in gene expression regulation. Functional annotation of genes with changes in transcript-level expression or containing DML revealed several enriched biological processes potentially involved in elevated pCO2 response, including apoptotic pathways and signal transduction, as well as reproductive functions. Taken together, these results suggest that DNA methylation may regulate gene expression variability to maintain homeostasis in elevated pCO2 conditions and could play a key role in environmental resilience in marine invertebrates.

physiology↗

bioRxiv2023

Characterizing transcriptomic responses to sediment stress across location and morphology in reef-building corals

Anthropogenic activities increase sediment suspended in the water column and deposition on reefs can be largely dependent on colony morphology. Massive and plating corals have a high capacity to trap sediments, and active removal mechanisms can be energetically costly. Branching corals trap less sediment, but are more susceptible to light limitation caused by suspended sediment. Despite deleterious effects of sediments on corals, few studies have examined the molecular response of corals with different morphological characteristics to sediment stress. To address this knowledge gap, this study assessed the transcriptomic responses of branching and massive corals in Florida and Hawai{square}i to varying levels of sediment exposure. Gene expression analysis revealed a molecular responsiveness to sediments across species and sites. Differentially Gene Expression (DEG) followed by Gene Ontology (GO) enrichment analysis identified that branching corals had the largest transcriptomic response to sediments, in developmental processes and metabolism, while significantly enriched GO terms were highly variable between massive corals, despite similar morphologies. Comparison of DEGs within orthogroups revealed that while all corals had DEGs in response to sediment, there was not a concerted gene set response by morphology or location. These findings illuminate the species specificity and genetic basis underlying coral susceptibility to sediments.

bioinformatics↗

bioRxiv2022

Characterization of a sperm motility signaling pathway in a gonochoric coral suggests conservation across sexual systems

Many marine invertebrates liberate their gametes into the water column broadcast spawning, where fertilization hinges upon the successful activation of sperm motility. Here, we investigated the molecular mechanisms underpinning sperm motility in the broadcast spawning coral Astrangia poculata. We found that cytosolic alkalinization activates the pH-sensing enzyme soluble adenylyl cyclase (sAC), followed by motility, in A. poculata sperm. In addition, we show for the first time in any cnidarian that sAC activity is required to activate protein kinase A (PKA) in sperm, and that PKA activity is required for the initiation of sperm motility. Ultrastructures of A. poculata sperm displayed morphological homology to other gonochoric cnidarians, and investigation of cnidarian proteomes revealed that sAC, the central signaling node in the sperm motility pathway, demonstrates broad structural and functional conservation across a diversity of cnidarian species. Ultimately, these results suggest that the role of sAC signaling in sperm motility is conserved between sperm from gonochoric and hermaphroditic corals, which is surprising given their morphological dissimilarities. This study also offers insight into the evolution of the mechanisms controlling metazoan sperm motility. Summary statementFor broadcast spawning marine invertebrates, the initiation of sperm motility is essential for fertilization. Here, we provide evidence for conservation of a sperm motility pathway across sexual systems in corals.

physiology↗