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A New Mouse Model for Cystinuria

The ICF Interview with Dr. Jay Tischfield of Rutgers University

June 13, 2006

(ICF) Dr Tischfield, Your lab has recently developed a population of mice that mimic the clinical manifestation of human cystinuria.

What is a "mouse model", and how was this population of cystinuric mice created?

(Dr. Tischfield) "A mouse model is a genetic replica (e.g., the same gene is defective as in humans) of a human disease. Sometimes, but not always, the clinical picture is the same of similar to the situation in humans. We used the methodology of gene targeting in cultured mouse embryonic stem cells (ESCs) to produce what are commonly known as "knockout" mice. We designed a targeting construct (a piece of DNA) based on the sequence of the mouse SLC3A1 gene. This is the mouse counterpart of the gene that is defective in Type I human cystinuria. The targeting construct was designed so that it would recombine with the SLC3A1 gene in the ESCs and replace part of the gene with a bacterial gene for antibiotic resistance. The result was ESCs with one copy of the SLC3A1 gene that was rendered defective. The "targeted" ESC's were mixed with normal mouse embryonic cells and surgically implanted in the uterus of a hormonally treated mouse. Some newborn mice that arose from these mixed early embryos were chimeric in that some parts of their bodies were derived from the targeted ESCs. We eventually found a male that produced sperm that contained the targeted SLC3A1 gene, and his offspring were mated to each other to produce mice in which both copies of the SLC3A1 gene were defective (i.e., genetic homozygotes for the defective gene). These mice had their urine tested and their kidneys and bladders were examined for stones."

(ICFs) In what way are these mice genetically similar to humans, causing them to form cystine stones?

(Dr. Tischfield) "The homozygous SLC3A1 gene "knockout" mice excrete cystine (including crystals) and dibasic amino acids in the urine. At 4 months of age, there are few cystine stones in the kidney, but there is massive stone accumulation in the bladder. Our initial studies suggest that SLC3A1 knockout mice mimic the causation and clinical manifestations of human cystinuria type I."

(ICF) What was your interest and motivation in developing a mouse model for cystinuria?

(Dr. Tischfield) "We have spent the past 20 years studying the molecular genetics of another (much rarer than cystinuria) human inborn error of metabolism known as APRT deficiency. This disease is characterized by kidney stones composed of a substance called DHA. This compound is quite different from cystine. About a decade ago, we produced a mouse model for APRT deficiency, using methods similar to those used for the cystinuric mouse. The "APRT knockout" had kidney stones similar to those observed in the human disease and other features (e.g., gender bias toward males) were noted. These mice could also be effectively treated with drugs used to treat the human disorder. We have spent the past few years studying the nature of kidney tissue injury by DHA crystals and this has progressed to a molecular study of altered gene expression in affected kidneys. APRT deficiency is different in some respects from the most common kidney diseases and we wanted to produce another mouse model to contrast with it. We chose cystinuria because it is relatively common and the stones are quite different from DHA stones. Also, we thought a cystinuria knockout could have clinical research utility."

(ICF) What does having a mouse model for cystinuria mean for the future of basic disease and pharmaceutical research related to cystinuria?

(Dr. Tischfield) "Our knockout mice will be used to study whether or not there is tissue injury, as reflected by changes in gene expression, in kidneys of affected animals. It is likely that the situation is similar to the human disease. On an immediately practical level, the mice could be used for research on drugs that might be helpful in treating cystinuria."

(ICF) What is the next step for this population of mice? (Is your group planning on conducting further research with them, or are they being sent out to other research groups?)

(Dr. Tischfield) "We are planning further research on the pathology of cystinuric mice and changes in gene expression that result from the disorder. We are willing to collaborate with other groups who may wish to study other aspects of the disease in these mice. The project is already collaborative, since the anatomical and pathological studies were done by Sharon Bledsoe and Dr. Andrew P. Evan of Indiana University School of Medicine."

(ICF) How does this mouse population differ from the 2 existing models published by Schlueter and Nunes in 2 separate articles for the September-2003 issue of Human Molecular Genetics?

(Dr. Tischfield) "The Nunes publication described mice with defects in the SLC7A9 gene, a defect similar to non Type I human cystinuria. This is not the most common form of cystinuria in the US.

The Schlueter paper describes mice treated with a powerful mutagen.
This is a shotgun approach, but several mice were identified as having impaired renal function. Study of one mouse showed a nucleotide replacement in the SLC3A1 gene. Apparently, this mutation abolishes most of the activity in the gene.

Our knockout is made quite differently and the clearly knocked out part of the genesis the most common region of the gene affected in humans.
Whether there are other differences remains to be seen."

(ICF) On behalf of the ICF, I thank you for sharing your time and knowledge.


Dr. Jay Tischfield is a Professor of Genetics & Chair (Professor of Pediatrics and Psychiatry, Robert Wood Johnson Medical School, UMDNJ) in the Department of Genetics/Human Genetics Institute at Rutgers University in Piscataway, New Jersey. Among many areas of research, Dr. Tischfield studies adenine phosphoribosyltransferase (APRT) deficiency, an inherited kidney stone-forming disease that makes cystinuria look common! Dr. Tischfield was also one of our honored presenters at the 2006 ICF Cystinuria Symposium in Chicago. Our continuing thanks to you for your support and your research.

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