Cystic Fibrosis Mouse Model

General Husbandry of CF Rats

Production of CF rats

The first CF rat model was created using gene targeting through zinc finger nucleases (ZFNs) in fertilized eggs. Additional models have been developed using ZFN and CRISPR technologies to knock out Cftr or introduce CF-relevant mutations. Once the mutations are introduced, CF rats are produced by breeding rats carrying one mutated Cftr allele, or heterozygous rats, and are born at the expected Mendelian ratio (1:2:1). CF male and female rats are not typically used for breeding. Although some CF female rats can produce offspring, the number of pups per litter is usually quite reduced (3 pups on average), and pups must be fostered for survival. CF male rats are completely infertile, because of the loss of the vas deferens due to the absence of Cftr.

Maintenance

CF rats are prone to intestinal obstruction leading to death. There are several different ways to alleviate intestinal obstruction through diet. The most effective way is to use laxative (colyte) in their drinking water. Additionally, CF rats have sensitive teeth, which require softened food and monthly trimming. These diet additives must be given throughout the course of their lifetime, from weaning on.

Disease Manifestations

Intestinal Disease

The most severe CF manifestation in rats is intestinal obstruction leading to death. This intestinal obstruction is due to a buildup of luminal mucus making it harder and harder for the movement of intestinal contents. The majority of death from intestinal obstruction occurs between 30 - 45 days of life, after rats start eating solid chow and are weaned from the dam. As mentioned above, this incidence of this obstruction can be reduced through addition of laxatives to the drinking water.

Growth

CF rats have reduced growth rates that begin shortly before weaning age. CF rats range from 10% to 50% of their littermates' weights depending on age and sex. The origin(s) of this reduced growth in CF rats is incompletely understood but may be due to decreased IGF-1 concentrations in the CF animals.⁴

Pulmonary Disease

Pulmonary disease in the CF rat have been shown to be progressive in nature, with some manifestations appearing early, and others delayed up to 6 months of age, and are detailed in Birket, et al, 2018.⁵ Airway pH is hyperacidic in the CF rat beginning at 1 month of age. Airway hydration is abnormal, with decreased airway surface liquid and increased solid content of the airway.

Submucosal gland development is delayed, only becoming hypertrophic in the CF rat large airways by 6 months of age. Correspondingly, intracellular mucus staining does not become abnormal until 6 months of age. These changes correlate with delayed mucus transport rates and increased hyperviscosity in situ in the large airways.

To date, CF rats primarily have been kept in a clean-living environment, and deaths due to pulmonary manifestations have been minimal.

Reproductive Dysfunction

Male: CF knockout male rats have been reported to have an intact vas deferens and/or epididymis at birth, with involution and atresia of both structures occurring between birth and 4 days of life.⁶ Consequently, CF knockout male rats are infertile and do not reproduce. The F508del male rats present with either a normal phenotype or absence of one or two vas deferens.²

Female: Abnormalities to the reproductive tract of CF female rats have not been studied. CF female rats are capable of reproduction; however, their litters tend to be much smaller than normal (~3 rats/litter), and the dams are not nutritionally sound enough for the pups to grow. Fostering is necessary for the pups and the dam to survive the lactation period.

Hepatic Disease

CF rats have not been observed to have hepatic disease at a young age. ¹ Hepatic manifestations in the older rats have not been studied.

Pancreatic Disease

There has been no evidence for exocrine pancreatic insufficiency in CF rats. Pancreatic pathology has been observed in older CF mice (at least 6 months of age) with progressive obstruction of the small ducts and acini. However, there is no data to date on whether this progression leads to exocrine pancreatic destruction with further aging.

Other Manifestations

Upper and lower incisors of CF rats are chalky white compared to the yellow/orange of their littermates. The difference in color can be detected at around 4 weeks of age and is thought to be due to abnormal enamel development in CF rats. Additionally, both upper and lower incisors must be trimmed on a routine basis to prevent malocclusion. This manifestation is useful for verifying that the rat is CF in combination with any genotyping that is completed.

CF rat strain	Mutation	Reference	Availability
Cftr^tm1sage	16bp deletion in exon 3	[1]	A
Cftr^KO	1bp insertion in exon 3	[2]
Cftr^F508del	F508del	[2]

1.	Tuggle KL, Birket SE, Cui X, et al. Characterization of defects in ion transport and tissue development in cystic fibrosis transmembrane conductance regulator (CFTR)-knockout rats. PLoS One 2014;9:e91253.
2.	Dreano E, Bacchetta M, Simonin J, et al. Characterization of two rat models of cystic fibrosis-KO and F508del CFTR-Generated by Crispr-Cas9. Animal Model Exp Med. 2019 Nov 25;2(4):297-311.
3.	CFTR Rat Models Core, Cystic Fibrosis Research Center, University of Alabama at Birmingham
4.	Stalvey MS, Havasi V, Tuggle KL, et al. Reduced bone length, growth plate thickness, bone content, and IGF-I as a model for poor growth in the CFTR-deficient rat. PLoS One 2017;12:e0188497.
5.	Birket SE, Davis JM, Fernandez CM, et al. Development of an airway mucus defect in the cystic fibrosis rat. JCI Insight 2018;3.
6.	Plyler ZE, Birket SE, Schultz BD, et al. Non-obstructive vas deferens and epididymis loss in cystic fibrosis rats. Mech Dev 2018.

Cystic Fibrosis Rat Model

General Characteristics

The Cystic Fibrosis Model

General Husbandry of CF Rats

Disease Manifestations

Available Strains

Contact for Information or Questions about this Model

References and Reviews