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Gen Comp Endocrinol. 2014 Sep 15;206:193-202. doi: 10.1016/j.ygcen.2014.07.007. Epub 2014 Jul 19.

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

Author information

1
Department of Biological Science, Graduate School of Science, Shizuoka University, Ohya 836, Shizuoka City, Shizuoka 422-8529, Japan.
2
Integrated Bioscience Section, Graduate School of Science and Technology, Shizuoka University, Ohya 836, Shizuoka City, Shizuoka 422-8529, Japan.
3
Department of Biology, Faculty of Science, Shizuoka University, Ohya 836, Shizuoka City, Shizuoka 422-8529, Japan.
4
Department of Life Science, School of Agriculture, Meiji University, 1-1-1 Higashi-mita, Kawasaki, Kanagawa 214-8571, Japan.
5
Department of Biological Science, Graduate School of Science, Shizuoka University, Ohya 836, Shizuoka City, Shizuoka 422-8529, Japan; Integrated Bioscience Section, Graduate School of Science and Technology, Shizuoka University, Ohya 836, Shizuoka City, Shizuoka 422-8529, Japan; Department of Biology, Faculty of Science, Shizuoka University, Ohya 836, Shizuoka City, Shizuoka 422-8529, Japan. Electronic address: sbmsuzu@ipc.shizuoka.ac.jp.

Abstract

Nkx2 homeodomain transcription factors are involved in various developmental processes and cell specification: e.g. in mammals, NKX2-1 is essential for thyroid-specific gene expression and thyroid morphogenesis. Among Nkx2 proteins, information is still very limited for Nkx2-4. In the present study, we have identified three distinct cDNAs encoding Nkx2-4 isoforms (Nkx2-4a, -b, and -c) from the rainbow trout thyroid tissue, and characterized their transcriptional properties. The trout Nkx2-4 proteins were all predicted to conserve three characteristic domains: the tinman-like amino terminal decapeptide, the NK2 homeodomain, and the NK2-specific domain, and also share 75-89% amino acid similarity. It was shown by dual luciferase assay that Nkx2-4a and Nkx2-4b, but not Nkx2-4c, significantly activated transcription from a cotransfected rat thyroglobulin (TG) promoter. An electrophoretic mobility shift assay indicated that all the Nkx2-4 isoforms could bind to the TG promoter, implying that the faint transcriptional activity of Nkx2-4c might result from some critical amino acid substitution(s) outside the homeodomain. RT-PCR analysis revealed similar tissue distribution patterns for Nkx2-4a and Nkx2-4b mRNAs. Both mRNAs were expressed abundantly in the thyroid, and weakly in the testis. On the other hand, Nkx2-4c mRNA was detected in the ovary as well as in the thyroid. The expression sites of Nkx2-4c mRNA were localized, by in situ hybridization histochemistry, to the ovarian granulosa cells and to the thyroid follicular cells. The results suggest that in the rainbow trout, Nkx2-4a and Nkx2-4b might play a major role in TG gene transcription whereas Nkx2-4c might have some functions in the ovary as well as the thyroid.

KEYWORDS:

Nkx2-1; Nkx2-4; Ovary; Rainbow trout; TTF-1; Thyroid transcription factor

PMID:
25051213
DOI:
10.1016/j.ygcen.2014.07.007
[Indexed for MEDLINE]

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