Abstract
Pancreatic insufficiency (PI) when left untreated results in a state of malnutrition due to an inability to absorb nutrients. Frequently, PI is diagnosed as part of a larger clinical presentation in cystic fibrosis or Shwachman–Diamond syndrome. In this study, a mouse model for isolated exocrine PI was identified in a mouse line generated by a transgene insertion. The trait is inherited in an autosomal recessive pattern, and homozygous animals are growth retarded, have abnormal immunity, and have reduced life span. Mice with the disease locus, named pequeño (pq), exhibit progressive apoptosis of pancreatic acinar cells with severe exocrine acinar cell loss by 8 wk of age, while the islets and ductal tissue persist. The mutation in pq/pq mice results from a random transgene insertion. Molecular characterization of the transgene insertion site by fluorescent in situ hybridization and genomic deletion mapping identified an approximately 210-kb deletion on Chromosome 3, deleting two genes. One of these genes, Serpini2, encodes a protein that is a member of the serpin family of protease inhibitors. Reintroduction of only the Serpini2 gene by bacterial artificial chromosome transgenic complementation corrected the acinar cell defect as well as body weight and immune phenotypes, showing that deletion of Serpini2 causes the pequeño phenotype. Dietary supplementation of pancreatic enzymes also corrected body size, body weight, and immunodeficiency, and increased the life span of Serpini2-deficient mice, despite continued acinar cell loss. To our knowledge, this study describes the first characterized genetic animal model for isolated PI. Genetic complementation of the transgene insertion mutant demonstrates that Serpini2 deficiency directly results in the acinar cell apoptosis, malabsorption, and malnutrition observed in pq/pq mice. The rescue of growth retardation, immunodeficiency, and mortality by either Serpini2 bacterial artificial chromosome transgenic expression or by pancreatic enzyme supplementation demonstrates that these phenotypes are secondary to malnutrition in pq/pq mice.
Highlights
The ability to ectopically express novel genes in the mouse genome via introduction of transgenic sequences has proved to be a valuable tool in the study of mammalian development and disease
Fluorescent in situ hybridization (FISH) analyses of metaphase spreads from three pequeno animals using the p3pTVA construct as a probe were performed
We concluded that the pequeno phenotype is due to a homozygous mutation that is linked to the transgene insertion and that the phenotype is inherited in an autosomal recessive pattern, as the heterozygotes had no apparent manifestations
Summary
The ability to ectopically express novel genes in the mouse genome via introduction of transgenic sequences has proved to be a valuable tool in the study of mammalian development and disease. In approximately 5% of the transgenic lines produced, an insertional mutation at the genomic integration locus occurs [1]. Often the insertion of the transgene is accompanied by a loss of surrounding genomic sequences and, dependent on the location of nearby coding and regulatory sequences, will produce an observable phenotype. We have been able to take advantage of such a transgene insertion/deletion event to identify and characterize a mouse model of pancreatic insufficiency (PI). The most common genetic disorder that exhibits PI is cystic fibrosis (CF), as 95% of patients with CF have pancreatic acinar cell loss, with fatty cell replacement and interstitial fibrosis [2]. Patients present with PI due to pancreatic acinar cell loss, and have clinical manifestations of short stature, neutropenia, pancytopenia and predisposition to acute myelogenous leukemia [3]
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