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one human year is equivalent to 18.25 and 50.34 rabbit days in the adult and post-senescence phases,
[34]
respectively . Thus, for most NDDs, the lifespan of rabbits is long enough for the observation of disease
progression.

PRODUCTION OF GENOME-MODIFIED RABBIT DISEASE MODELS VIA CRISPR-CAS
SYSTEM
The production of disease models that recapitulate the pathological features of human disease is an
important approach to investigating the pathogenesis of the disease. Artificially induced disease models can
exhibit clinical features of some NDDs. For instance, hydroxydopamine, 1-methyl-4-phenyl-1,2,3,6-
[47]
tetrahydropyridine, rotenone, and paraquat are commonly used in the induction of Parkinson’s disease .
However, many NDDs are caused by pathological mutation of the disease-related gene, and an induction
model cannot fully recapitulate the whole pathological pathway of diseases caused by genetic disorders .
[1]
Therefore, to elucidate the whole pathogenesis process of neuron degeneration, the production of animal
models that carry pathological mutations that mimic human disease is necessary.

With the development of gene-editing tools, efficient and accurate genome modification has become
achievable. To date, various genome-edited rabbits have been constructed, as shown in Table 2. In 2013, the
CRISPR-Cas9 system was harnessed for efficient targeted genome editing in eukaryotic cells [99,100] . Moreover,
with the further development of research on CRISPR-Cas systems, the CRISPR-Cas systems and their
derivates can facilitate targeted gene knockout (KO), knockin (KI), activation, suppression, and single-base
substitution. Presently, various genome editing tools based on CRISPR-Cas systems are widely used in
multiple species, including non-human primates, large non-primate animals, rodents, and rabbits [101-103] .

[101]
The first CRISPR-Cas-mediated gene KO in rabbits was successfully generated in 2014 [Table 2];
however, full-length gene KO can only recapitulate diseases caused by loss of function. To mimic diseases
caused by gain-of-function mutation due to point mutation, more accurate gene manipulation is needed.
Furthermore, more than 50,000 disease-causing mutations in humans are point mutations; therefore, a
novel system that can mediate single base substitution is needed. Since 2017, the development of cytosine
and adenine base editing systems can facilitate efficient C to T and A to G base substitutions, which can
facilitate precise gene manipulation . Such systems were identified as having ideal editing efficiency in
[104]
rabbits [Table 2]; the efficiency of cytidine base editor (CBE) and adenine base editor (ABE) in rabbits after
co-microinjection of base editor mRNA and sgRNA are 53%-88% and 44%-100%, respectively . The
[90]
following refinement of base editors has overcome or reduced the limitations of PAM sequences and the
incidence of bystander activities [92,105] . At this stage, base editing systems are capable of inducing disease
causative missense and nonsense mutations in rabbits to generate disease models.

Although base editing systems can induce four transversion mutations, it is impossible for such systems to
induce the other eight transversion mutations. Moreover, the generation of bystander mutations cannot be
completely avoided when there are multiple C or A in the editing window. Importantly, conventional gene
editing systems cannot induce efficient single base or oligonucleotide insertions and deletions. Therefore, it
is hard to generate disease models with fragment shift mutations. Fortunately, the development of prime
editing systems solved such problems in 2019. The system, which is based on the target binding capacity of
the CRISPR-Cas9 system and the retro-transcription activity of retrotrancripsase, can facilitate the whole
genome “search and replace” activity in organisms. Prime editor was successfully used in generating a Tay-
Sachs disease (TSD) rabbit model in 2021 [Table 2], which is a model of neurological disease generated by
prime editor-mediated four base insertion .
[98]