Thyrotropin-releasing hormone precursor: characterization in rat brain

Area of Science:

• Neuroendocrinology
• Molecular Biology
• Genetics

Background:

• Thyrotropin-releasing hormone (TRH) is a key regulator of the hypothalamic-pituitary-thyroid axis.
• The precise precursor and processing of mammalian TRH have not been fully elucidated.

Purpose of the Study:

• To characterize the precursor protein of mammalian thyrotropin-releasing hormone (TRH).
• To investigate the cellular localization of TRH precursor gene expression in the rat brain.

Main Methods:

• Screening of a rat hypothalamic lambda gt11 library using an antiserum against a synthetic TRH prohormone peptide.
• Nucleotide sequencing of immunopositive complementary DNA (cDNA).
• In situ hybridization to rat brain sections.

Main Results:

• The nucleotide sequence encoded a 29,247-molecular weight protein containing five copies of the TRH sequence (Gln-His-Pro-Gly) flanked by paired basic amino acids.
• Potential cleavage sites suggest the generation of additional non-TRH peptides.
• In situ hybridization localized pre-proTRH cDNA expression to neurons in the parvocellular division of the paraventricular nucleus.

Conclusions:

• Mammalian TRH is derived from a larger precursor protein through posttranslational processing.
• The precursor's ability to generate multiple TRH copies likely amplifies hormone production.
• TRH precursor gene expression is concentrated in specific hypothalamic neurons, consistent with immunohistochemical findings.