Angiotensin-(1-7) plays an important role in regulating spermatogenesis in Trachemys scripta elegans under salinity stress

Impact of environmental salinity on the MAPK-NFAT5 pathway in Trachemys scripta elegans and its role in osmoregulaton

Globally, sea level rise (SLR) leads to salinization of coastal freshwater, in where organisms might be affected and in turn promote osmoregulation and adaptation in response to freshwater salinization. Trachemys scripta elegans a freshwater turtle species, exhibits remarkable tolerance to varying salinity environments, yet the underlying regulatory mechanisms remain poorly understood. This study aimed to elucidate the molecular mechanisms of osmoregulation in this species based on previous RNA-seq data. Our findings revealed that when exposed to 5 PSU (5 ‰) and 15 PSU (15 ‰) salinities, the turtles exhibited increased concentrations of ions (Na+, K+) and urea in urine, along with elevated osmotic pressures in both plasma and urine. Additionally, the protein levels of aquaporins (AQPs) and transporters of ions and organic osmolytes in the kidney were upregulated in saline water. Notably, the transcriptional level of the hypertonic regulator NFAT5 was significantly elevated, accompanied by an increase in phosphorylated NFAT5 levels in the nucleus of renal tubular epithelial cells. Furthermore, we observed upregulated phosphorylated levels of MAPKs in saline water. The use of MAPK inhibitors effectively blocked the transcription of NFAT5 and osmoregulatory target genes. Collectively, these results suggest that T. scripta elegans activates the MAPK-NFAT5 signaling pathway to modulate osmotic pressure in adaptation to saline water environments. Our study provides valuable insights into the osmoregulatory responses of aquatic organisms to saline environments and aids in understanding the adaptability of organisms inhabiting coastal areas facing rising sea levels.

Effect of Salinity Stress on Gut-Brain-Gonad Axis in the Red-Eared Slider (Trachemys scripta elegans)

The red-eared slider (Trachemys scripta elegans) can adapt to brackish water, which can endanger its biodiversity. Spermatogonial stem cells (SSCs) are essential for establishing and maintaining spermatogenesis and are regulated by the gut-brain-gonad axis. However, the effect of salinity on SSCs is unclear. We investigated the influence of salinity stress on the composition of the gut microbiota in T. s. elegans to determine whether it regulates SSC self-renewal and differentiation via the gut-brain-gonad axis. Three salinity groups (0‰, 5‰, and 10‰) were used in this study, and samples were obtained after 6 months of feeding. The mRNA expression of self-renewing genes (GFRα-1, RAS, and ERK) and meiotic initiation genes (RARα, NRG3, and ERBB4) in SSCs decreased with increasing salinity, indicating that salinity affects renewal and differentiation. In addition, harmful bacteria such as Enterococcus and Clostridium were increased in the S10 group, and lower levels of g_norank_f_Eubacteriaceae were negatively associated with γ-aminobutyric acid (GABA), whereas higher Turicibacter levels were positively associated with GABA levels, resulting in increased GABA content in the S5 group. The results show that salinity affects the secretion of neurotransmitters in the brain and negatively regulates the synthesis of reproductive hormones by changing the composition of intestinal microorganisms and metabolites, which affect SSC function. In conclusion, salinity influences the reproductive ability of T. s. elegans through the gut-brain-gonad axis. This study provides a new perspective for understanding the adaptation of T. s. elegans to brackish water.

Embryonic development and transcriptomic analysis in red-eared slider Trachemys scripta elegans under salinity stress

The elevated salinity in freshwater causes a serious threat to the survival and reproduction of freshwater organisms. The effect of salinity on embryonic development of freshwater turtles is little known. In this study, we investigated the embryonic morphology and underlining mechanism of red-eared slider (Trachemys scripta elegans) in different salinities incubated environment (2.5 ppt and 5 ppt). Results showed that salinity caused various forms of malformed embryos, including brain hypoplasia, eye defects, skeletal dysplasia, deformities of carapace, plastron, limb in the embryo. Severely, salinity could lead to embryos decease. Transcriptome analysis showed that differentially expressed genes induced by salinity primarily enriched in development pathways, metabolism pathways, disease pathways as well as cell processes through KEGG enrichment analysis. In addition, in early and middle embryonic developmental stages, the mRNA expression of apoptotic genes (p38 and bax) significantly increased, whereas anti-apoptotic gene bcl-2 decreased in salinities incubated environment. These findings demonstrated that salinity inhibited the process of embryonic development and damaged organogenesis of turtles through promoting apoptotic pathways.