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Gene expression, function, and diversity of Nkx2-4 in the rainbow trout, Oncorhynchus mykiss

Youji Uemae1, Joe Sakamoto2, Yoshie Hidaka2

  • 1Department of Biological Science, Graduate School of Science, Shizuoka University, Ohya 836, Shizuoka City, Shizuoka 422-8529, Japan.

General and Comparative Endocrinology
|July 23, 2014
PubMed

Insights

Rainbow trout Nkx2-4 transcription factors show distinct roles in gene regulation. Nkx2-4a and Nkx2-4b activate thyroglobulin gene transcription, while Nkx2-4c has ovarian and thyroid functions.

Area of Science:

  • Developmental Biology
  • Molecular Endocrinology
  • Comparative Genomics

Background:

  • Nkx2 homeodomain transcription factors regulate crucial developmental processes and cell specification.
  • NKX2-1 is vital for thyroid function in mammals, but Nkx2-4 functions remain largely uncharacterized.
  • Understanding Nkx2-4 isoforms in fish can provide insights into conserved and divergent roles of this gene family.

Purpose of the Study:

  • To identify and characterize rainbow trout Nkx2-4 isoforms (Nkx2-4a, -b, and -c) from thyroid tissue.
  • To investigate the transcriptional properties and DNA-binding capabilities of these isoforms.
  • To determine the tissue-specific expression patterns of Nkx2-4 isoforms in rainbow trout.

Main Methods:

  • Identification of Nkx2-4 cDNAs from rainbow trout thyroid tissue.
  • Dual luciferase reporter assays to assess transcriptional activation of the rat thyroglobulin (TG) promoter.
  • Electrophoretic mobility shift assays (EMSA) to evaluate DNA-binding affinity to the TG promoter.
  • RT-PCR and in situ hybridization histochemistry to analyze mRNA tissue distribution.

Main Results:

  • Three rainbow trout Nkx2-4 isoforms (Nkx2-4a, -b, -c) were identified, sharing high amino acid similarity.
  • Nkx2-4a and Nkx2-4b significantly activated the TG promoter, while Nkx2-4c showed minimal activity despite binding the promoter.
  • Nkx2-4a and Nkx2-4b mRNAs were abundant in the thyroid and weakly in the testis; Nkx2-4c mRNA was found in the ovary and thyroid.

Conclusions:

  • Rainbow trout Nkx2-4a and Nkx2-4b likely play a significant role in regulating thyroglobulin gene transcription.
  • Nkx2-4c may possess distinct functions in the ovary and thyroid, potentially due to specific amino acid variations.
  • This study elucidates isoform-specific functions of Nkx2-4 transcription factors in a teleost model, contributing to the understanding of thyroid development and gene regulation.
Keywords:
Nkx2-1Nkx2-4OvaryRainbow troutTTF-1Thyroid transcription factor

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