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Molecular and Cellular Biology, March 2001, p. 1833-1840, Vol. 21, No. 5
Institut National de la Santé et de la
Recherche Médicale U397, Endocrinologie et Communication
Cellulaire, Institut Fédératif de Recherche Louis Bugnard,
C.H.U. Rangueil, 31403 Toulouse Cedex 04,1
Centre de Biologie du Développement, UMR 5547,
Université Paul Sabatier, 31062 Toulouse Cedex
04,3 and Institut de Pharmacologie
et Biologie Structurale du Centre National de la Recherche
Scientifique, 31077 Toulouse Cedex 04,2 France
Received 11 September 2000/Returned for modification 6 November
2000/Accepted 5 December 2000
The expression of c-myc proto-oncogene, a key regulator
of cell proliferation and apoptosis, is controlled at different
transcriptional and posttranscriptional levels. In particular, the
c-myc mRNA contains an internal ribosome entry site (IRES)
able to promote translation initiation independently from the classical
cap-dependent mechanism. We analyzed the variations of
c-myc IRES activity ex vivo in different proliferating cell
types, and in vivo in transgenic mice expressing a bicistronic dual
luciferase construct. c-myc IRES efficiency was compared to
that of encephalomyocarditis virus (EMCV) IRES under the same
conditions. The c-myc IRES was active but with variable
efficiency in all transiently transfected cell types; it was also
active in the 11-day- old (E11) embryo and in some tissues of the E16
embryo. Strikingly, its activity was undetected or very low in all
adult organs tested. In contrast, EMCV IRES was very active in most
cell types ex vivo, as well as in embryonic and adult tissues. These
data suggest a crucial role of IRES in the control of c-myc
gene expression throughout development, either during embryogenesis
where its activity might participate in cell proliferation or later on,
where its silencing could contribute to the downregulation of
c-myc expression, whose deregulation leads to tumor formation.
0270-7306/01/$04.00+0 DOI: 10.1128/MCB.21.5.1833-1840.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
c-myc Internal Ribosome Entry Site
Activity Is Developmentally Controlled and Subjected to a Strong
Translational Repression in Adult Transgenic Mice
*
Corresponding author. Mailing address: Institut
National de la Santé et de la Recherche Médicale U397,
Endocrinologie et Communication Cellulaire, Institut
Fédératif de Recherche Louis Bugnard, C.H.U. Rangueil,
31403 Toulouse Cedex, France. Phone: 33 (5) 61 32 21 42. Fax: 33 (5) 61 32 21 41. E-mail: pratsac{at}rangueil.inserm.fr.
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