Transcriptional Profiling of the Megabladder Mouse - A Unique Model of Bladder Dysmorphogenesis

Recent studies in our lab have identified a mutant mouse model of obstructive nephropathy designated mgb for megabladder. Homozygotic mgb mice (mgb-/-) develop lower urinary tract obstruction in utero due to a lack of bladder smooth muscle differentiation. This defect is the result of a random transgene insertion into chromosome 16 followed by a translocation of this fragment into chromosome 11. In an effort to identify potential gene targets affected in mgb mice, we performed transcriptional profiling on embryonic day 15 (E15) mgb-/- bladders using both a Chromosome 11/16 Custom GeneChip Array and the Affymetrix Mouse Genome 430 2.0 GeneChip. This analysis identified no definitive mis-expressed gene targets on chromosome 11. In contrast, mgb-/- mice significantly over-expressed a cluster of gene products located on the translocated fragment of chromosome 16 including urotensin II-related peptide (Urp), which was shown to be preferentially over-expressed in developing mgb-/- bladders. Immunohistochemical studies indicated that the spatial distribution of Urp was altered in mgb-/- bladders, while biochemical studies suggested a potential role for Urp in modifying smooth muscle cell phenotype in vitro. Pathway analysis of mgb microarray data showed dysregulation of at least 60 gene products associated with the differentiation of smooth muscle. In conclusion, the results of this study indicate that the molecular pathways controlling normal smooth muscle development are severely altered in mgb-/- bladders, and provide the first evidence that Urp may play a critical role in bladder smooth muscle development.

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