Differential expression of gluconeogenesis-related transcripts in a freshwater zooplankton model organism suggests a role of the Cori cycle in hypoxia tolerance

Transcriptional atlas of Daphnia magna

Transcriptomics studies are more likely to achieve predictive results when they rely on tissue- and cell-specific transcriptional data. Identification of cell types in novel model organisms by their transcriptional profiles is difficult without data on transcriptional differences among major tissues and anatomical features. Here we report the first dataset on tissue- and organ-specific transcriptomics in freshwater plankton crustacean Daphnia magna, reporting markers of embryos, hemocytes, gut, carapace, antennae-2, and head, as well as the remaining carcass. Embryos are the most transcriptionally different from adults' features, with antennae and carapace being the most differentiated among them. We demonstrate that transcriptional markers of embryos vs. adults and of various adult anatomical features can be used to provide validation and functional explanation to published differential expression in response to environmental factors like infection, hypoxia, toxicants, or kairomones; to annotate Daphnia single cell data; and to ask questions about transcriptional diversification within extended gene families.

Impact of hypoxia on glucose metabolism and hypoxia signaling pathways in juvenile horseshoe crabs Tachypleus tridentatus

Marine hypoxia poses a significant challenge in the contemporary marine environment. The horseshoe crab, an ancient benthic marine organism, is confronted with the potential threat of species extinction due to hypoxia, making it an ideal candidate for studying hypoxia tolerance mechanisms. In this experiment, juvenile Tachypleus tridentatus were subjected to a 21-day trial at DO:2 mg/L (hypoxia) and DO:6 mg/L conditions. The experimental timeline included a 14-day exposure phase followed by a 7-day recovery period. Sampling occurred on days 0, 7, 14, and 21, where the period from day 14 to day 21 corresponds to seven days of recuperation. Several enzymatic activities of important proteins throughout this investigation were evaluated, such as succinate dehydrogenase (SDH), phosphofructokinase (PFK), hexokinase (HK), lactate dehydrogenase (LDH), and pyruvate kinase (PK). Concurrently, the relative expression of hexokinase-1 (HK), hypoxia-inducible factor 1-alpha inhibitor (FIH), and hypoxia-inducible factor 1-alpha (HIF-1α), pyruvate dehydrogenase phosphatase (PDH), succinate dehydrogenase assembly factor 4 (SDH), and Glucose-6-phosphatase (G6Pase) were also investigated. These analyses aimed to elucidate alterations in the hypoxia signaling pathway and respiratory energy metabolism. It is revealed that juvenile T. tridentatus initiated the HIF pathway under hypoxic conditions, resulting in an upregulation of HIF-1α and FIH-1 gene expression, which in turn, influenced a shift in metabolic patterns. Particularly, the activity of glycolysis-related enzymes was promoted significantly, including PK, HK, PKF, LDH, and the related HK gene. In contrast, enzymes linked to aerobic respiration, PDH, and SDH, as well as the related PDH and SDH genes, displayed down-regulation, signifying a transition from aerobic to anaerobic metabolism. Additionally, the activity of gluconeogenesis-related enzymes such as PK and G6Pase gene expression were significantly elevated, indicating the activation of gluconeogenesis and glycogenolysis pathways. Consequently, juvenile T. tridentatus demonstrated an adaptive response to hypoxic conditions, marked by changes in respiratory energy metabolism modes and the activation of hypoxia signaling pathways.