Comparative analysis of two newly established Cre rat lines, NeuN-Cre and Thy1-Cre, for neurological research.

Background: The Cre/loxP system is most popular in mice, but its application in rats has largely lagged far behind. The rat is vital laboratory animal, especially in toxicological and neurological studies. Generating genetic tools to manipulate neurons in rats could benefit neurological research.

Methods: Using the CRISPR/Cas9 system, we inserted a Cre cassette into endogenous Thy1 and NeuN loci. Thy1-Cre rats featured a downstream P2A-linked insertion, while NeuN-Cre was inserted at the transcriptional start site. The Cre activity was assessed by crossing with a Cre reporter (Rosa26^imCherry) rat and through analyzing mCherry expression patterns. The specificity of cell type was further confirmed by immunofluorescence with NeuN antibody. Phenotypic consequences were assessed by crossing with ND1^LSL rats to deplete ND1, followed by monitoring weight/survival and conducting motor function tests.

Results: We generated two neuron-specific rats (Thy1-Cre and NeuN-Cre), which exhibited high neuron-specific Cre expression in brain and spinal cord with minor leakage in other tissues. Thy1-Cre showed minor leakage in spleen, lung and kidney while NeuN-Cre showed minor leakage in spleen and kidney. ND1^Thy1-Cre and ND1^NeuN-Cre rats both showed decreased body weights and survival times. The ND1^NeuN-Cre rats died within two weeks, while ND1^Thy1-Cre rats lived longer with impaired motor function.

Conclusions: We successfully generated two neuron-specific NeuN-Cre and Thy1-Cre rats, and systemically analyzed their expression pattern.