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Mol. Cell. Biol., Aug 1996, 4495-4503, Vol 16, No. 8
A Dupressoir and T Heidmann
Intracisternal A-particle (IAP) sequences are endogenous retrovirus- like
mobile elements, or retrotransposons, present at 1,000 copies in the mouse
genome. These elements transpose in a replicative manner via an RNA
intermediate and its reverse transcription, and their transposition should
therefore be tightly controlled by their transcription level. To analyze
the in vivo pattern of expression of these retrovirus-like elements, we
constructed several independent transgenic mice with either a complete IAP
element marked with an intron or with the IAP promoter, or long terminal
repeat (LTR), alone controlling the expression of a lacZ reporter gene with
a nuclear localization signal. For all transgenic lines analyzed, IAP
expression as determined by reverse transcription-PCR analysis was found to
be essentially restricted to the male germ line. Furthermore, in situ 5-
bromo-4-chloro-3-indolyl-beta-D-galactopyranoside (X-Gal) staining of all
organs disclosed specific beta-galactosidase-positive blue cells only
within the testis, found as patches along the seminiferous tubules and
often organized as assemblies of 2, 4, 8, or 16 cells. Histochemical
analyses of tissues from 13.5-day-old embryos to adults demonstrated that
this LTR activity is restricted to gonocytes and premeiotic
undifferentiated spermatogonia. Finally, analysis of the methylation status
of both transgenes and endogenous IAP LTRs demonstrated identical patterns,
with methylation in somatic tissues and hypomethylation in the testis.
Transgenic mice therefore reveal an intrinsic, highly restricted IAP
expression which had escaped detection in previous global Northern (RNA)
blot analyses and with possible strong biological relevance, as IAP
activation specifically within the germ line might be a way to generate
diversity at the evolutionary level without being deleterious to
individuals.
Copyright © 1996, American Society for Microbiology
Germ line-specific expression of intracisternal A-particle retrotransposons in transgenic mice
Unite de Physicochimie et Pharmacologie des Macromolecules Biologiques, Institut Gustave Roussy, France.
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