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???displayArticle.abstract??? Thyroid hormones (THs) induce metamorphosis in amphibians, causing dynamic changes, whereas mammalian newborns undergo environmental transition from placenta to open air at birth. The similarity between amphibian metamorphosis and the mammalian perinatal periods has been repeatedly discussed. However, a corresponding developmental gene expression analysis has not yet been reported. In this study, we examined the developmental gene expression profiles in the brain and liver of Xenopus tropicalis during metamorphosis climax and compared them to the respective gene expression profiles of newborn rodents. Many upregulated genes identified in the tadpolebrain during metamorphosis are also upregulated in the rodent brain during the first three postnatal weeks when the TH surge occurs. The upregulation of some genes in the brain was inhibited in thyroid hormone receptor α (TRα) knockout tadpoles but not in TRβ-knockout tadpoles, implying that brain metamorphosis is mainly mediated by TRα. The expression of some genes was also increased in the liver during metamorphosis climax. Our data suggest that the rodent brain undergoes TH-dependent remodeling during the first three postnatal weeks as observed in X. tropicalis during the larva-to-adult metamorphosis.
25430089 A Grant-in-Aid for Scientific Research from the Ministry of Education, Culture, Sports, Science and Technology, Japan, 26440057 A Grant-in-Aid for Scientific Research from the Ministry of Education, Culture, Sports, Science and Technology, Japan
Figure 1
Developmental expression of neural tissueâ€related genes in the X. tropicalis brain. qRTâ€PCR was conducted using total cellular brain RNA and geneâ€specific primers (Supporting Information Table S2). The relative mRNA expression level of the indicated gene to EFâ€1α mRNA is presented. Data are expressed as mean ± SD (biological replicate number = 5–7)
Figure 2
Developmental expression of synapseâ€related genes in the X. tropicalis brain. qRTâ€PCR was conducted using total cellular brain RNA and geneâ€specific primers (Supporting Information Table S2). The relative mRNA expression level of the indicated gene to EFâ€1α mRNA is presented. Data are expressed as mean ± SD (biological replicate number = 5–7)
Figure 3
Expression of neural tissueâ€related and synapseâ€related genes in the brain of NF stage 61 wildâ€type and TRâ€knockout tadpoles. Total cellular RNA was extracted from brains of NF stage 61 wildâ€type, TRαâ€knockout, and TRβâ€knockout tadpoles, and qRTâ€PCR was conducted using geneâ€specific primers (Supporting Information Table S2). The relative mRNA expression level of the indicated gene to EFâ€1α mRNA is presented. Data are expressed as mean ± SD. Biological replicate numbers of wildâ€type, TRαâ€knockout, and TRβâ€knockout brain samples are five, five, and four, respectively. Statistical significance by comparison of TRαâ€knockout tadpoles with wildâ€type and TRβâ€knockout tadpoles were assessed using the Tukey's test. *p < 0.05, **p < 0.01
Figure 4
Developmental expression of albumin and urea cycle enzyme genes in liver of X. tropicalis. qRTâ€PCR was conducted using total cellular liver RNA and geneâ€specific primers (Supporting Information Table S2). The relative mRNA expression level of the indicated gene to EFâ€1α mRNA is represented. Data are expressed as mean ± SD (biological replicate number = 4–6)
Figure 5
Developmental expression of TRα and TRβ genes in the brain and liver of X. tropicalis. qRTâ€PCR was conducted using total cellular brain and liver RNAs and geneâ€specific primers (Supporting Information Table S2). The relative mRNA expression level of the indicated gene to EFâ€1α mRNA is presented. Data are expressed as mean ± SD. The biological replicate numbers are 5–7 (a, b) and 4–6 (c, d)
Supplementary Figure 1. Expression of neural tissue-related genes in the brains of stage-61 wild-type and
TR-knockout tadpoles. Total cellular RNA was extracted from brains of NF stage-61 wild-type, TRα knockout,
and TRβ knockout tadpoles, and qRT-PCR was conducted using gene-specific primers (Table S2 in Supporting
Information). The relative mRNA expression level of the indicated gene to EF-1α mRNA is presented. Data are
expressed as mean ± SD. Biological replicate numbers of wild-type, TRα-knockout, and TRβ-knockout brain
samples are five, five, and four, respectively.
Supplementary Figure 2. Developmental expression of albumin and urea cycle enzyme genes in liver
of R. catesbeiana. qRT-PCR was conducted using total cellular liver RNA and gene-specific primers (Table
S2 in Supporting Information). Tadpoles were staged according to the Nieukoop and Faber method. The
relative mRNA expression level of the indicated gene to EF-1α mRNA is represented.
