Gene expression of immune and neuroendocrine-related genes and biometric data of small-spotted catshark embryos (Scyliorhinus canicula) after six days of exposure to deoxygenation and hypoxia.

Description

The global oxygen inventory has been declining worldwide, primarily due to climate change. However, the effects of low oxygen levels on shark neuroendocrinology and immunology are not understood. This study investigated the neuroendocrine response and immune competence of the head and trunk tissues of early (EE; before pre-hatching) and late embryos (LE) of small-spotted catshark (Scyliorhinus canicula) under six days of deoxygenation (DO; 93% O2 of air saturation) and hypoxic conditions (26% O2). Catshark embryos were resilient to DO, showing only minor changes in gene expression for melanotransferrin and a 10% decline in survival. Under hypoxia, growth remained unaffected; however, survival decreased by 31%, exceptionally in LE, highlighting inadequate adaptive responses. The developmental stage affected the expression of stress and immune response genes, pointing to critical developmental shifts in response mechanisms. The EE stage showed a greater stress response under hypoxia compared to LE, with several immune and neuroendocrine genes upregulated, while hypoxia-inducible factor 1 alpha levels decreased. The energy demands associated with coping with hypoxia compromised immune and endocrine functions, raising concerns about long-term species survival under climate change. These findings highlight the need for further research on sharks' resilience to environmental challenges and the interactions of metabolic pathways. Here we show the gene expression (expressed as 2^ΔΔCT) of immune and neuroendocrine-related genes in head and trunk samples of early (EE) and late embryos (LE), and biometric data of small-spotted catshark (Scyliorhinus canicula) after six days of exposure to deoxygenation (air saturation = 93%) and hypoxia (air saturation = 26%).

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The embryo wet mass was recorded using a Sartorius balance (CPA225D, Germany). The total length was measured (from the tip of the snout to the tip of the tail) to calculate Fulton's condition factor (K), which was determined using the total mass (g) divided by the total length (cm) cubed × 100. The embryo was dissected into two parts: head from the tip of the head to the end of the gills (H), and trunk region (organs; O) from the pectoral to the anal fin (excluding gills). The developmental status of each embryo in the different treatment regimens was assessed according to the scale of  Musa et al (2018) under-candling and was confirmed visually after euthanasia. EE and LE were selected, and stage four was used as the cut-off (pre-hatching). Results of qPCR expression in head and trunk samples of early (EE) and late embryos (LE) of small-spotted catshark (Scyliorhinus canicula; ncontrol = 11, nDO = 10, nHypoxia = 13) after six days of exposure to deoxygenation (DO; air saturation = 93%) and hypoxia (air saturation = 26%) were normalized using the geometric mean of ribosomal protein L13 (RPL13) and S29 (RPS29) and normalized data were expressed as 2^ΔΔCT. A – iron metabolism (meltf – melanotransferrin, fer - ferritin heavy chain, fch – ferrochelatase); B – innate immune genes (lys – lysozyme G-like, tnfr - tumor necrosis factor receptor SF1A associated via death domain, perf1 - perforin 1, irf2 - interferon regulatory factor 2, ifn – interferon gamma-like, nfkrf – nuclear factor kappa B (NFKB) repressing factor); C – neuroendocrine genes (tshr – TSH receptor, thrb – thyroid hormone receptor beta, pomc – proopiomelanocortin a, tpo – thyroid peroxidase, gh - growth hormone, ghr – growth hormone receptor, mchr1,2 – melanin-concentrating hormone receptors 1 and 2), and D - hypoxia-related genes (hif1a – hypoxia-inducible factor 1 alpha).

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