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Anuran amphibians undergo major physiological and immunological changes following metamorphosis. Genes of the major histocompatibility complex (MHC) code for receptors important for vertebrate adaptive immunity. We used qPCR to measure skinMHC expression in six different ontological stages of Ranaornativentris (n = 10 per stage); normalized MHC class I and II expression at the mRNA level was significantly higher in stage 28 (mid-larval) compared to stages 24/25 (early-larval) tadpoles. Subsequent transcriptomic analyses of three tadpole (early-, mid-, and late-larval) stages of R.ornativentris and model species Xenopus tropicalis focused on mRNA expression of immune-related genes in the skin. Normalized expression of most MHC class I and II transcripts in both species were significantly higher in mid- and late-larval stages compared to early-larval stage. In addition, gene ontology (GO) analyses of differentially expressed transcripts revealed several immune-related GO terms that were significantly upregulated from the mid-larval stage. Our study provides evidence that both MHC class I and II is expressed during development in both R.ornativentris and X. tropicalis.
Figure 1. Overview of Rana ornativentris and Xenopus tropicalis samples used for qPCR and transcriptome analyses in this study. a R. ornativentris stage approximations based on Tahara [19,20]. b X. tropicalis stage approximations based on Nieuwkoop and Faber [23]. Full stage approximations in Table S1. Images of frogs in all figures are not to scale (source: Q. Lau for R. ornativentris, Nieuwkoop and Faber (1994) via Xenbase for X. tropicalis).
Figure 2. Boxplot of (A) MHC class I and (B) MHC class II expression in mRNA of Rana ornativentris tadpoleskin during six ontological stages and other samples: stage 24/25 body, and adult skin and spleen. MHC expression values from qPCR were normalized by the GAPDH control gene and log-transformed for normality (log-normalized). * p < 0.05, *** p < 0.0001.
Figure 3. Venn diagrams of gene ontology (GO) terms enriched in skin of early- (E), mid- (M) and late- (L) larval stages from (A) Rana ornativentris and (B) Xenopus tropicalis. Number of immune-related enriched GO terms are in black (full list in Tables S5 and S6), and total number of enriched GO terms belonging to the ‘biological process’ parent category are in grey and also represented by circle sizes. Examples of enriched immune-related GO terms are listed in comparisons between stages (full list in Tables S5 and S6).
Figure S1. Gel electrophoresis following PCR amplification of GAPDH, MHC class I, and MHC class II from early-, mid-, and late-larval stages of Xenopus laevis and X. tropicalis tadpoleskin cDNA samples (n =3 per stage per species).
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