Direct Comparison of Constitutive Rax-Cre Transgenic Drivers That Activate in the Mouse Embryonic Eye Field.

Area of Science:

• Developmental biology
• Genetics
• Ophthalmology

Background:

• The Rax/Rx gene is crucial for early eye development, with its expression progressively restricted.
• Constitutive Cre recombinase mouse lines, Rx3-Cre and Rax-Cre BAC Tg, are utilized by vision researchers to study Rax/Rx gene function.
• Understanding the precise Cre activity of these lines is essential for accurate lineage tracing in ocular development.

Purpose of the Study:

• To directly compare the prenatal ocular and extraocular Cre activities of Rx3-Cre and Rax-Cre BAC transgenic mouse lines.
• To evaluate the utility of these Cre drivers for studying embryonic and postnatal eye development.
• To inform the use of these tools in modeling congenital eye diseases.

Main Methods:

• Mating Rx3-Cre or Rax-Cre BAC transgenic male mice with Cre-dependent lineage tracer Ai9/tdTomato mice.
• Evaluating live and fixed tissue expression at multiple developmental stages, from optic vesicle onward.
• Imaging of whole embryos and immunolabeled cryosectioned material.

Main Results:

• Rx3-Cre recapitulates endogenous RAX expression but shows unexpected Cre activity in periocular mesenchyme and potential germline expression.
• Rax-Cre BAC driver accurately recapitulates endogenous RAX expression in the embryonic and postnatal eye, with minor unexpected limb expression.
• Both lines demonstrate Cre activity in optic vesicle-derived tissues.

Conclusions:

• A systematic analysis of Rx3-Cre and Rax-Cre BAC drivers during eye development is provided.
• These Cre drivers are valuable for recapitulating severe congenital eye diseases.
• Lineage reporting and littermate controls are strongly recommended when using conditional targeting strategies for optic vesicle-derived tissues.