Biochemical bases of growth variation during development: a study of protein turnover in pedigreed families of bivalve larvae (Crassostrea gigas)

Ocean Acidification Alters Developmental Timing and Gene Expression of Ion Transport Proteins During Larval Development in Resilient and Susceptible Lineages of the Pacific Oyster (Crassostrea gigas)

Ocean acidification (OA) adversely impacts initial shell formation of bivalve larvae. Despite many studies observing large differences in developmental success between distinct genetic populations of bivalves exposed to OA, few studies have investigated the molecular mechanisms that enable resilient larvae to build their initial shell in aragonite-undersaturated conditions. This knowledge is key to their ecological and economical conservation. Herein, we used a genetic-selection program for Crassostrea gigas to produce a resilient and susceptible larval lineage to OA. The resilient and susceptible larvae were sampled every 3 h over a 24-h period in aragonite-undersaturated and control conditions. The susceptible lineage failed to develop a larval shell in aragonite-undersaturated conditions, whereas 52% of the resilient lineage developed to D-larvae by 24 h post fertilisation. We measured the expression of 23 genes involved in initial shell formation by RT-qPCR, which revealed significant genotype-by-time and environment-by-time interactions for the transcription of these genes. Aragonite-undersaturated conditions upregulated a single gene encoding a protein involved in ion transport, Na⁺ K⁺ ATPase, in both the resilient and susceptible lineage. These results were corroborated by a second experiment involving 25 pair-mated C. gigas families exposed to aragonite-undersaturated and control conditions. Our findings indicate C. gigas have a fixed capacity to modulate expression of genes involved in initial shell formation in response to OA. Thus, phenotypic differences to OA between the resilient and susceptible lineage are likely explained by other cellular processes, such as bioenergetics or protein translation.

A biomimetic natural sciences approach to understanding the mechanisms of ageing in burden of lifestyle diseases

The worldwide landscape of an ageing population and age-related disease brings with it huge socio-economic and public healthcare concerns across nations. Correspondingly, monumental human and financial resources have been invested in biomedical research, with a mission to decode the mechanisms of ageing and how these contribute to age-related disease. Multiple hallmarks of ageing have been identified that are common across taxa, highlighting their fundamental importance. These include dysregulated mitochondrial metabolism and telomeres biology, epigenetic modifications, cell-matrix interactions, proteostasis, dysregulated nutrient sensing, stem cell exhaustion, inflammageing and immuno-senescence. While our understanding of the molecular basis of ageing is improving, it remains a complex and multifactorial process that remains to be fully understood. A key aspect of the shortfall in our understanding of the ageing process lies in translating data from standard animal models to humans. Consequently, we suggest that a 'biomimetic' and comparative approach, integrating knowledge from species in the wild, as opposed to inbred genetically homogenous laboratory animals, can provide powerful insights into human ageing processes. Here we discuss some particularities and comparative patterns among several species from the animal kingdom, endowed with longevity or short lifespans and unique metabolic profiles that could be potentially exploited to the understanding of ageing and age-related diseases. Based upon lessons from nature, we also highlight several avenues for renewed focus in the pathophysiology of ageing and age-related disease (i.e. diet-microbiome-health axis, oxidative protein damage, adaptive homoeostasis and planetary health). We propose that a biomimetic alliance with collaborative research from different disciplines can improve our understanding of ageing and age-related diseases with long-term sustainable utility.

Different protein metabolic strategies for growth during food-induced physiological plasticity in echinoid larvae

Food-induced morphological plasticity, a type of developmental plasticity, is a well-documented phenomenon in larvae of the echinoid echinoderm, Dendraster excentricus A recent study in our lab has shown that this morphological plasticity is associated with significant physiological plasticity for growth. The goal of the current study was to measure several aspects of protein metabolism in larvae growing at different rates to understand the mechanistic basis for this physiological growth plasticity. Larvae of D. excentricus were fed rations of 1000 algal cells ml^-1 (low-fed larvae) or 10,000 algal cells ml^-1 (high-fed larvae). Relative protein growth rate was 6.0 and 12.2% day^-1 for low- and high-fed larvae, respectively. The energetic cost of protein synthesis was similar for the two treatments at 4.91 J mg^-1 protein synthesized. Larvae in both treatments used about 50% of their metabolic energy production to fuel protein synthesis. Mass-specific rates of protein synthesis were also similar. Large differences in mass-specific rates of protein degradation were observed. Low-fed larvae had relatively low rates of degradation early in development that increased with larval age, surpassing those of high-fed larvae at 20 days post-fertilization. Changes in protein depositional efficiency during development were similar to those of larval growth efficiency, indicating that differences in protein metabolism are largely responsible for whole-organism growth plasticity. Low-fed larvae also had alanine transport rates that were 2 times higher than those of high-fed larvae. In total, these results provide an explanation for the differences in growth efficiency between low- and high-fed larvae and allow for a more integrated understanding of developmental plasticity in echinoid larvae.

Differing thermal sensitivities of physiological processes alter ATP allocation

Changes in environmental temperature affect rate processes at all levels of biological organization. Yet the thermal sensitivity of specific physiological processes that affect allocation of the ATP pool within a species is less well understood. In this study of developmental stages of the Pacific oyster, Crassostrea gigas, thermal sensitivities were measured for growth, survivorship, protein synthesis, respiration and transport of amino acids and ions. At warmer temperatures, larvae grew faster but suffered increased mortality. An analysis of temperature sensitivity (Q ₁₀ values) revealed that protein synthesis, the major ATP-consuming process in larvae of C. gigas, is more sensitive to temperature change (Q ₁₀ value of 2.9±0.18) than metabolic rate (Q ₁₀ of 2.0±0.15). Ion transport by Na⁺/K⁺-ATPase measured in vivo has a Q ₁₀ value of 2.1±0.09. The corresponding value for glycine transport is 2.4±0.23. Differing thermal responses for protein synthesis and respiration result in a disproportional increase in the allocation of available ATP to protein synthesis with rising temperature. A bioenergetic model is presented illustrating how changes in growth and temperature affect allocation of the ATP pool. Over an environmentally relevant temperature range for this species, the proportion of the ATP pool allocated to protein synthesis increases from 35 to 65%. The greater energy demand to support protein synthesis with increasing temperature will compromise energy availability to support other essential physiological processes. Defining the trade-offs of ATP demand will provide insights into understanding the adaptive capacity of organisms to respond to various scenarios of environmental change.

Effects of seawater salinity and pH on cellular metabolism and enzyme activities in biomineralizing tissues of marine bivalves

Molluscan shell formation is a complex energy demanding process sensitive to the shifts in seawater CaCO₃ saturation due to changes in salinity and pH. We studied the effects of salinity and pH on energy demand and enzyme activities of biomineralizing cells of the Pacific oyster (Crassostrea gigas) and the hard-shell clam (Mercenaria mercenaria). Adult animals were exposed for 14 days to high (30), intermediate (18), or low (10) salinity at either high (8.0-8.2) or low (7.8) pH. Basal metabolic cost as well as the energy cost of the biomineralization-related cellular processes were determined in isolated mantle edge cells and hemocytes. The total metabolic rates were similar in the hemocytes of the two studied species, but considerably higher in the mantle cells of C. gigas compared with those of M. mercenaria. Cellular respiration was unaffected by salinity in the clams' cells, while in oysters' cells the highest respiration rate was observed at intermediate salinity (18). In both studied species, low pH suppressed cellular respiration. Low pH led to an upregulation of Na⁺/K⁺ ATPase activity in biomineralizing cells of oysters and clams. Activities of Ca²⁺ ATPase and H⁺ ATPase, as well as the cellular energy costs of Ca²⁺ and H⁺ transport in the biomineralizing cells were insensitive to the variation in salinity and pH in the two studied species. Variability in cellular response to low salinity and pH indicates that the disturbance of shell formation under these conditions has different underlying mechanisms in the two studied species.

Differential responses to ocean acidification between populations of Balanophyllia elegans corals from high and low upwelling environments

Ocean acidification (OA), the global decrease in surface water pH from absorption of anthropogenic CO₂ , may put many marine taxa at risk. However, populations that experience extreme localized conditions, and are adapted to these conditions predicted in the global ocean in 2,100, may be more tolerant to future OA. By identifying locally adapted populations, researchers can examine the mechanisms used to cope with decreasing pH. One oceanographic process that influences pH is wind-driven upwelling. Here we compare two Californian populations of the coral Balanophyllia elegans from distinct upwelling regimes, and test their physiological and transcriptomic responses to experimental seawater acidification. We measured respiration rates, protein and lipid content, and gene expression in corals from both populations exposed to pH levels of 7.8 and 7.4 for 29 days. Corals from the population that experiences lower pH due to high upwelling maintained the same respiration rate throughout the exposure. In contrast, corals from the low upwelling site had reduced respiration rates, protein content and lipid-class content at low pH exposure, suggesting they have depleted their energy reserves. Using RNA-Seq, we found that corals from the high upwelling site upregulated genes involved in calcium ion binding and ion transport, most likely related to pH homeostasis and calcification. In contrast, corals from the low upwelling site downregulated stress response genes at low pH exposure. Divergent population responses to low pH observed in B. elegans highlight the importance of multi-population studies for predicting a species' response to future OA.