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Ontogenetic pattern of thyroid hormone receptor expression in the human testis
E A Jannini1, A Crescenzi, N Rucci
1Department of Experimental Medicine, University of L'Aquila, Italy.
The Journal of Clinical Endocrinology and Metabolism
|September 22, 2000
Summary
Thyroid hormone receptors (TRs) alpha1 and alpha2 are present in human testes, with TRalpha2 levels consistently higher than TRalpha1. TRbeta is undetectable, and TRalpha expression is concentrated in Sertoli cells during development.
Area of Science:
- Endocrinology
- Reproductive Biology
- Molecular Biology
Background:
- Thyroid hormone nuclear receptors (TRs) play crucial roles in development and metabolism.
- Specific TR isoform expression patterns in the human testis are not fully elucidated.
- Understanding TR distribution is vital for comprehending thyroid hormone action in testicular function.
Purpose of the Study:
- To investigate the spatiotemporal distribution of TRalpha1, TRalpha2, and TRbeta mRNA in human testicular tissue.
- To determine the developmental expression profile of TR isoforms in the fetal and adult human testis.
- To identify the specific cell types expressing TRs within the human testis.
Main Methods:
- Northern blot analysis to detect mRNA expression levels.
- Semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) for isoform-specific quantification.
- In situ hybridization to localize TR mRNA within testicular tissue.
Main Results:
- Both TRalpha1 and TRalpha2 isoforms were detected in the human testis, with TRalpha2 consistently expressed at higher levels than TRalpha1 across all ages.
- TRalpha1 expression significantly decreased from fetal development to adulthood, becoming faintly detectable in adults.
- TRbeta mRNA was undetectable in testicular tissue at all developmental stages studied, confirmed by both Northern blot and PCR.
Conclusions:
- The human testis exclusively expresses TRalpha isoforms, with TRbeta being absent.
- TRalpha1 and TRalpha2 are localized within Sertoli cells, particularly during fetal and prepubertal stages.
- The observed developmental changes in TRalpha isoform expression suggest a critical window for thyroid hormone action in testicular development, potentially explaining conditions like pre-pubertal hypothyroidism-induced macroorchidism.