Enhancer adoption by an LTR retrotransposon generates viral-like particles, causing developmental limb phenotypes.

Area of Science:

• Genomics
• Developmental Biology
• Molecular Biology

Background:

• Transposable elements (TEs) are mobile genetic sequences present in mammalian genomes.
• TE silencing is essential to prevent genome instability and insertional mutations.
• The role of TE activation in disease without direct gene disruption remains unclear.

Purpose of the Study:

• To investigate if TE activation can cause disease by affecting gene regulation.
• To explore the mechanism by which TE insertions impact embryonic development.

Main Methods:

• Analysis of LTR retrotransposon insertion upstream of the Fgf8 gene in mice.
• Investigation of co-expression patterns between the TE and Fgf8 during development.
• Assessment of viral-like particle (VLP) assembly and its effect on cell apoptosis.
• Rescue experiments by mutating the retrotransposon coding sequence.

Main Results:

• Failure to silence an LTR retrotransposon near the Fgf8 gene led to their co-expression in developing mouse embryos.
• VLP assembly in Fgf8-expressing cells induced apoptotic cell death in developing limbs.
• This resulted in limb malformations analogous to human ectrodactyly.
• Mutating the retrotransposon coding sequence rescued the observed phenotype.

Conclusions:

• TE insertions can be integrated into local genomic regulatory networks.
• VLP production by TEs in post-implantation embryos can lead to developmental abnormalities.
• This study reveals a novel mechanism of TE-induced disease independent of direct gene disruption.