THYROID-HORMONE REGULATION OF GERM CELL-SPECIFIC EF-1-ALPHA EXPRESSION DURING METAMORPHOSIS OF XENOPUS-LAEVIS

In situ hybridization was used to follow the distribution of the mRNAs encoding the somatic form of elongation factor 1 alpha (EF-1 alpha S) and the germinal counterparts of this factor, thesaurin a and EF-1 al pha O, throughout metamorphosis in the gonads of Xenopus laevis tadpol es. EF-1 alpha S mRNA is detected before metamorphosis in both the som atic and germ cells of the gonads. In contrast, thesaurin a and EF-1 a lpha O mRNAs are first detected in spermatogonia and oogonia at stages 60-62, corresponding to the climax of metamorphosis and to the peak o f circulating thyroid hormone. To determine whether thyroid hormone, t he instigator of metamorphosis, is involved in regulating the expressi on of the germinal gene EF-1 alpha O, Xenopus XTC cells were transfect ed with an EF-1 alpha O promoter sequence inserted in front of the luc iferase reporter gene. Addition of T3 to the cell culture medium induc ed a dose-dependent increase in transcription from the EF-1 alpha O pr omoter. This effect was enhanced when the construct was cotransfected with an expression vector for a Xenopus thyroid hormone receptor. Our data show that germ cells switch from a somatic to a germ-cell specifi c mode of expression during metamorphosis Furthermore, this switch app ears to be induced by thyroid hormone.