A thyroid-stimulating hormone β subunit (TSHβ) cDNA encoding both signal peptide and mature TSHβ molecule was cloned from a cDNA library constructed from total RNA of the bullfrog (Rana catesbeiana) adenohypophysis. The bullfrog TSHβ mRNA was estimated by Northern blot analysis to be approximately 1 kb. The deduced amino acid sequence showed 40-61% homologies with the sequences of TSH β subunits of other vertebrates. Using the cDNA as a probe, we measured changes in mRNA expression in metamorphosing tadpoles of R. catesbeiana. The TSH β subunit mRNA level increased progressively throughout prometamorphic stages, reaching its maximum at the end of prometamorphosis. The maximum level was maintained throughout early and mid climax, declining at late climax. These results, together with previously obtained data on plasma prolactin and pituitary prolactin mRNA levels, as well as thyroid hormone levels, are discussed in relation to metamorphic changes occurring in the bullfrog larvae. (C) 2000 Academic Press.
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