Increased Cdx protein dose effects upon axial patterning in transgenic lines of mice
Stephen J Gaunt1, Deborah Drage, Richard C Trubshaw
1Department of Development and Genetics, The Babraham Institute, Babraham, Cambridge, UK. stephen.gaunt@bbsrc.ac.uk
Abstract:
To investigate the link between Cdx protein concentration and axial patterning in embryos, we made lines of mice OE1, OE2 and OE4 that overexpress each of the Cdx genes Cdx1, Cdx2 and Cdx4, respectively. The lines carry Cdx transgenes under the transcriptional control of their own promoter/enhancer elements. Transgenic embryos show Cdx transcription at 8.5 to 8.7 days within normal spatial domains for Cdx expression (primitive streak/tailbud), yet, overall, they contain elevated levels of Cdx proteins. Increased doses of Cdx proteins result in homeotic shifts in vertebral types along most of the vertebral column, with transformations being most obvious within the cervical region. Most of the shifts are anterior-to-posterior transformations and the anterior limits of these are commonly skull/vertebra 1 (v1) for OE1, v1/v2 for OE2 and v7 for OE4. OE embryos display anterior shifts in the expression of a Hoxa7/lacZ reporter within neural, paraxial and lateral plate mesoderm tissues. Hoxa7/lacZ expression commences at the normal time in OE1 and OE4 embryos. OE2 embryos display a forward shift in the gradient of Cdx2 protein along the axis, suggesting that a Cdx morphogen gradient model could account, at least in part, for the homeotic shifts in vertebral types. OE mice display additional defects: forelimb deficiencies in OE1, multiple tail axes, vertebral mis-alignments and axial truncations in OE2.
Insights
Altering Cdx gene expression in mice embryos significantly impacts axial patterning, causing homeotic shifts in vertebral types. This suggests Cdx proteins play a crucial role in establishing embryonic body plans.
Area of Science:
- Developmental Biology
- Genetics
- Embryology
Background:
- Caudal-type homeobox (Cdx) genes are critical regulators of embryonic axial patterning.
- Understanding the precise role of Cdx protein concentration in determining vertebral identity is essential.
Purpose of the Study:
- To investigate the relationship between Cdx protein levels and the development of axial structures in mouse embryos.
- To determine how overexpression of Cdx1, Cdx2, and Cdx4 affects vertebral identity and patterning.
Main Methods:
- Generation of transgenic mouse lines (OE1, OE2, OE4) overexpressing Cdx1, Cdx2, and Cdx4, respectively.
- Analysis of Cdx gene transcription and protein levels in transgenic embryos.
- Assessment of homeotic shifts in vertebral types and expression patterns of developmental reporters like Hoxa7/lacZ.
Main Results:
- Overexpression of Cdx genes led to elevated Cdx protein levels and homeotic shifts in vertebral types, particularly in the cervical region.
- Anterior-to-posterior transformations were observed, with anterior limits varying based on the specific Cdx gene overexpressed.
- Anterior shifts in Hoxa7/lacZ reporter expression indicated altered patterning along the neural, paraxial, and lateral plate mesoderm.
- A forward shift in Cdx2 protein gradient in OE2 embryos supported a morphogen gradient model for axial patterning.
Conclusions:
- Cdx protein concentration directly influences homeotic shifts in vertebral identity during embryonic development.
- A Cdx morphogen gradient model may partially explain the observed vertebral transformations.
- Cdx gene manipulation can lead to additional developmental defects, including limb deficiencies and axial abnormalities.
