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Xenopus laevis survives seasonal droughts by entering a hypometabolic state known as aestivation. One of the mechanisms employed by X. laevis to mitigate aestivation-induced tissue atrophy is gene regulation of pro-survival proteins. We further expand on the role of anti-apoptotic signaling in X. laevis by investigating the effect of signal transducer and activator of transcription (STAT) signaling on downstream anti-apoptotic genes in control and dehydrated liver and skeletal muscle of X. laevis. Herein, we found that STAT signaling is differentially regulated between tissues. STAT3 signaling in the liver and STAT5 signaling in skeletal muscle lead to the selective upregulation of downstream anti-apoptotic proteins. Additionally, pro-apoptotic STAT1 signaling is found to be attenuated in both tissues during dehydration stress. Overall, our results indicate an important role for anti-apoptotic proteins during dehydration stress and their contribution in mitigating aestivation-induced atrophy.
FIGURE 1. Relative protein expression of phosphorylated STAT transcription factors, p‐STAT1Tyr701, p‐STAT2Tyr690, p‐STAT3Tyr705, p‐STAT3Ser727, p‐STAT5Tyr694, and p‐STAT6Tyr641, in (a) liver tissue and (b) skeletal muscle tissue during control (c), medium (MD), and high‐dehydration (HD) conditions of Xenopus laevis. Data are mean ± SEM (n = 4 independent trials), with asterisks denoting values determined to be statistically significantly (p < 0.05) different from control values by a one‐way analysis of variance (ANOVA) with Dunnett's post‐hoc test.
FIGURE 2. Relative protein expression in X. laevis nuclear extracts of (a) p‐STAT3Tyr705 and p‐STAT3Ser727 of control and HD liver, and (b) p‐STAT5Tyr694 from control, MD, and HD skeletal muscle. Data are mean ± SEM (n = 4 independent trials), with asterisks denoting values determined to be statistically significantly (p < 0.05) different from control values by either (a) Student's t‐test or (b) a one‐way ANOVA with Dunnett's post‐hoc test.
FIGURE 3. Relative nuclear DNA binding of (a) p‐STAT3Tyr705 in liver and (b) p‐STAT5Tyr694 in skeletal muscle of control and HD X. laevis as determined by an enzyme‐linked immunosorbent assay (ELISA). Data are mean ± SEM (n = 4 independent trials), with asterisks denoting values determined to be statistically significantly (p < 0.05) different from control values by Student's t‐test.
FIGURE 4. Electrophoretic mobility shift assay (EMSA) of nuclear X. laevis liver extract in control and HD, showing a shift from low molecular weight unbound probes to the higher molecular weight p‐STAT‐DNA complex. The probe was designed to bind both p‐STAT3 and p‐STAT5.
FIGURE 5. Relative mRNA transcript levels of STAT3 and STAT5 downstream targets, bcl‐2 and mcl‐1, in (a) liver and (b) skeletal muscle of control, MD, and HD X. laevis. Data are mean ± SEM (n = 4 independent trials), with asterisks denoting values determined to be statistically significantly (p < 0.05) different from control values by a one‐way ANOVA with Dunnett's post‐hoc test.
FIGURE 6. Relative protein expression of the STAT downstream targets, total Bcl‐2, p‐Bcl‐2Thr56, p‐Bcl‐2Ser70, and Mcl‐1 in (a) liver and (b) skeletal muscle of control, MD, and HD X. laevis. Data are mean ± SEM (n = 4 independent trials), with asterisks denoting values determined to be statistically significantly (p < 0.05) different from control values by a one‐way ANOVA with Dunnett's post‐hoc test.
