Cystic Fibrosis Sheep Model

General Characteristics

Lifespan: 10-12 years

Gestation time: 142-152 days

Number of lambs: 1-2 lambs

Age to sexual maturity: Ewes, 7-9 months; Rams 7-8 months

Adult weight: Ewes, 68-90 kg; Rams, 100-124 kg

Breed: American Romney

Sheep

The Cystic Fibrosis Model

The first cystic fibrosis (CF) sheep model was published in 2018.1The model was generated using CRISPR/Cas9 gene editing of sheep fetal fibroblasts that were subsequently reprogrammed and used to clone the CF sheep (Figure 1). Cystic fibrosis sheep shared a similar clinical presentation with human CF patients including intestinal obstruction, pancreatic dysfunction, liver biliary fibrosis, and male infertility.

General Husbandry of CF Sheep

Production of CF sheep

The CF sheep was created by using CRISPR/Cas9 gene editing and somatic cell nuclear transfer (SCNT or cloning), a common approach for production of large animal models.2First, small insertions or deletions (indels) were introduced into Exon 2 and Exon 11 of the sheep CFTR gene in sheep fetal fibroblast cells. Subsequently, these cells were used for cloning to produce CFTR null lambs. Cystic fibrosis sheep can also be produced by breeding sheep carrying one mutated CFTR allele (i.e., heterozygous CFTR+/- sheep), and affected offspring are born at the expected Mendelian ratio (1:2:1).

Sheep Production

Figure1

Maintenance

The homozygous (CFTR-/-) sheep model is characterized by severe intestinal obstruction at birth (meconium ileus [MI]) that requires euthanasia soon after birth (within 48 hours). Therefore, this model can be primarily used for understanding prenatal development of CF pathology and symptoms and the development of prenatal therapeutic approaches. Current efforts are underway to genetically modify the CF sheep to correct the intestinal obstruction phenotype.

Disease Manifestations

 

Intestinal Disease

Extensive intestinal obstruction is present in all CFTR-/- lambs. This severe abnormality leads to early death of the lambs. The obstruction is caused by accumulation of mucus in the colon or aboral small intestine that leads to obstruction in the jejunum, ileum, or spiral colon. Excessive intestinal or colonic mucus accumulation is first detectable during gestation when the fetus is around 80 to 100 days.

 

Pulmonary Disease

Sheep lungs are grossly normal in the CFTR-/- lambs. The absence of detectable disease in this organ is not unexpected as lung pathology develops mainly after birth in humans.

 

Pancreatic Disease

Pancreatic hypoplasia is present in both CFTR-/- (73%) and CFTR+/- (60%) sheep. Pancreatic fibrosis is evident in 40% of the CFTR-/- animals, while not observed in  CFTR+/- animals, and thus, it is considered a phenotype resulting from loss of CFTR function.

 

Hepatic Disease

The gallbladder in 80% of the animals is hypoplastic and half to one third of the expected size. Intrahepatic cholestasis, and/or portal fibrosis and biliary hyperplasia, resembling biliary fibrosis is present in 86% the CFTR-/- lambs.

 

Male Genital Duct Dysfunction

All CFTR-/- males lack grossly visible or histologically detectable vas deferens. All CFTR+/- male lambs had normal male genital ducts. It is expected that CFTR-/- males will be infertile.

Available Strains

CFTR+/-

CFTR-/- timed pregnancies

*Cells are also available from animals upon request

Contact for Information or Questions about this Model

e-mail: irina.polejaeva@usu.edu

References and Reviews

1. Fan, Z., et al., A sheep model of cystic fibrosis generated by CRISPR/Cas9 disruption of the CFTR gene. JCI Insight, 2018. 3(19).
2. Polejaeva, I., et al., Livestock in biomedical research: history, current status and future prospective. Reproduction, Fertility and Development, 2016. 28(2): p. 112-124.
3. Cooney, A.L., et al., Cystic Fibrosis Gene Therapy: Looking Back, Looking Forward. Genes (Basel), 2018. 9(11).
4. Semaniakou, A., et al., Animal Models in the Pathophysiology of Cystic Fibrosis. Front Pharmacol, 2019. 9:1475.