Red-eared Slider Turtle Trachemys Scripta Research Articles

Adenosine Monophosphate-Activated Protein Kinase Signaling Regulates Lipid Metabolism in Response to Salinity Stress in the Red-Eared Slider Turtle Trachemys scripta elegans.

Aquatic animals have developed various mechanisms to live in either hyperionic or hypoionic environments, and, as such, not many species are capable of surviving in both. The red-eared slider turtle, Trachemys scripta elegans, a well-known freshwater species, has recently been found to invade and inhabit brackish water. Herein, we focus on some of the metabolic adaptations that are required to survive and cope with salinity stress. The regulation of the adenosine monophosphate (AMP)-activated protein kinase (AMPK), a main cellular “energy sensor,” and its influence on lipid metabolism were evaluated with a comparison of three groups of turtles: controls in freshwater, and turtles held in water of either 5‰ salinity (S5) or 15‰ salinity (S15) with sampling at 6, 24, and 48 h and 30 days of exposure. When subjected to elevated salinities of 5 or 15‰, AMPK mRNA levels and AMPK enzyme activity increased strongly. In addition, the high expression of the peroxisome proliferator activated receptor-α (PPARα) transcription factor that, in turn, facilitated upregulation of target genes including carnitine palmitoyltransferase (CPT) and acyl-CoA oxidase (ACO). Furthermore, the expression of transcription factors involved in lipid synthesis such as the carbohydrate-responsive element-binding protein (ChREBP) and sterol regulatory element-binding protein 1c (SREBP-1c) was inhibited, and two of their target genes, acetyl-CoA carboxylase (ACC) and fatty acid synthase (FAS), were significantly decreased. Moreover, exposure to saline environments also increased plasma triglyceride (TG) content. Interestingly, the content of low-density lipoprotein cholesterol (LDL-C) and total cholesterol (TC) in plasma was markedly higher than the control in the S15 group after 30 days, which indicated that lipid metabolism was disrupted by chronic exposure to high salinity. These findings demonstrate that activation of AMPK might regulate lipid metabolism in response to salinity stress through the inhibition of lipid synthesis and promotion of lipid oxidation in the liver of T. s. elegans. This may be an important component of the observed salinity tolerance of these turtles that allow for invasion of brackish waters.

Dmrt1 induces the male pathway in a turtle species with temperature-dependent sex determination.

The molecular mechanism underlying temperature-dependent sex determination (TSD) has been a long-standing mystery; in particular, the thermosensitive genetic triggers for gonadal sex differentiation are largely unknown. Here, we have characterized a conserved DM domain gene, Dmrt1, in the red-eared slider turtle Trachemys scripta (T. scripta), which exhibits TSD. We found that Dmrt1 has a temperature-dependent, sexually dimorphic expression pattern, preceding gonadal sex differentiation, and is capable of responding rapidly to temperature shifts and aromatase inhibitor treatment. Most importantly, loss- and gain-of-function analyses provide solid evidence that Dmrt1 is both necessary and sufficient to initiate male development in T. scripta Furthermore, the DNA methylation dynamics of the Dmrt1 promoter are tightly correlated with temperature and could mediate the impact of temperature on sex determination. Collectively, our findings demonstrate that Dmrt1 is a candidate master male sex-determining gene in this TSD species, consistent with the idea that DM domain genes are conserved during the evolution of sex determination mechanisms.

A timecourse analysis of systemic and gonadal effects of temperature on sexual development of the red-eared slider turtle Trachemys scripta elegans

Temperature dependent sex determination (TSD) is the process by which the environmental temperature experienced during embryogenesis influences the sex of an organism, as in the red-eared slider turtle Trachemys scripta elegans. In accord with current paradigms of vertebrate sex determination, temperature is believed to exert its effects on sexual development in T. scripta entirely within the middle third of development, when the gonad is forming. However, whether temperature regulates the transcriptome in T. scripta early embryos in a manner that could influence secondary sex characteristics or establish a pro-male or pro-female environment has not been investigated. In addition, apart from a handful of candidate genes, very little is known about potential similarities between the expression cascade during TSD and the genetic cascade that drives mammalian sex determination. Here, we conducted an unbiased transcriptome-wide analysis of the effects of male- and female-promoting temperatures on the turtle embryo prior to gonad formation, and on the gonad during the temperature sensitive period. We found sexually dimorphic expression reflecting differences in steroidogenic enzymes and brain development prior to gonad formation. Within the gonad, we mapped a cascade of differential expression similar to the genetic cascade established in mammals. Using a Hidden Markov Model based clustering approach, we identified groups of genes that show heterochronic shifts between M. musculus and T. scripta. We propose a model in which multiple factors influenced by temperature accumulate during early gonadogenesis, and converge on the antagonistic regulation of aromatase to canalize sex determination near the end of the temperature sensitive window of development.

Distribution and characteristics of endogenous digestive enzymes in the red-eared slider turtle, Trachemys scripta elegans

Distribution and properties of the main digestive enzymes including protease and amylase, from stomach, pancreas and the anterior, middle and posterior intestine of the adult red-eared slider turtle Trachemys scripta elegans were studied at various pHs and temperatures. The optimum temperature and pH for protease in stomach, pancreas and the anterior, middle and posterior intestine were 40 degrees C, 2.5; 50 degrees C, 8.0; 50 degrees C, 7.0; 50 degrees C, 8.0; and 50 degrees C, 8.5; respectively. The optimum temperature and pH for amylase in stomach, pancreas and anterior, middle and posterior intestine were 40 degrees C, 8.0; 30 degrees C, 7.5; 40 degrees C, 7.0; 50 degrees C, 8.0; and 50 degrees C, 8.0; respectively. Under the optimum conditions, the order of protease activity from high to low was of pancreas, stomach and the anterior, posterior and middle intestine; the activity of amylase in descending order was of anterior intestine, pancreas, posterior intestine, middle intestine and stomach.

Sequence and expression analysis of WT1 and Sox9 in the red-eared slider turtle, Trachemys scripta.

Temperature-dependent sex-determination (TSD) is a phenomenon that has been characterized at the ecological, morphological, and endocrinological levels in some reptilian species. We have begun to investigate TSD at the level of molecular development by cloning, sequencing, and analyzing the expression of two genes, WT1 and Sox9, in the red-eared slider turtle Trachemys scripta. We obtained almost full-length cDNA clones for WT1 and Sox9 that were greater than 73% identical to the human homologues at the nucleotide level. WT1 was expressed in urogenital tissue at all developmental stages examined (Yntema stages 12-20) at incubation temperatures that produce males (26 degrees C) or females (32 degrees C). Sox9 was also expressed throughout these same stages, but some differences were observed. At both 26 degrees C and 32 degrees C Sox9 was expressed in the mesonephroi and the undifferentiated gonads until Yntema stage 20, when only the gonad from the 26 degrees C embryos expressed a high level. In addition, there were two transcripts of Sox9 at all stages, but the relative proportion of the two transcripts differed at the two temperatures. Although the similarities in gene expression between a TSD species and other species with genotypically determined sex probably reflect the common features of organogenesis, differences may illustrate unique mechanisms for TSD.