Renal hypodysplasia (RHD) is a congenital disease that results in abnormally small and dysplastic kidneys. RHD is associated with chronic renal failure since the excretory portion does not differentiate properly and renal tubules progressively distend due to decreased filtration efficiency. Genes directing dysmorphogenetic events in RHD remain obscure. This project utilizes a radiation induced mutation in the 3H1 mouse called Brachyrrhine (Br) that inherits RHD as an autosomal semidominant trait. The overall goal of this project is to determine the genetic basis of RHD using Br as a model. Previously, Br was mapped to the distal portion of murine chromosome 17 (chr17). The first specific aim of this project is to undertake a high resolutioin microsatellite linkage analysis of distal chrl 7 to isolate a 100 - 500 kilobase region utilizing a large back cross mouse DNA sample followed by an in silico analysis of the candidate gene region using Celera and Sanger Gene Discovery databases.
The second aim i s to screen renal tissues of mutant and normal embyos at gestational days 13 and 14 for candidate gene expression using Northern blot analysis. It is expected that a gene deletion will be identified since the mutant phenotype and inheritance pattern is consistent with a radiation induced doubled stranded break and segment deletion. If a deletion is indicated, renal mRNA expression patterns in the mutant will be compared to corresponding normal renal tissue using RT-PCR and in situ hybridization, while associated protein analysis will utilize immunohistochemical methods.
Specific aim 3 will sequence each exon in the candidate region using 3H1+/'+ and Br/Br DNA samples. Thus, the mutation in 3H1 Br will be determined even if a deletion is not found in Specific Aim 2. Additional methods will be utilized including SSCP and heteroduplex analysis to identify mutations in exons that may have been missed. As a result of this project, the gene responsible for RHD in 3H1 Br/Br mice will be identified. This sequence will be subjected to a mouse-human homology search and it is likely that a corresponding human gene will be identified since distal murine chr17 shares a high degree of sequence affinity with human chr 2p21.1.
