DEVELOPMENT AND REGENERATIVE ABILITY OF BLADDER IN THE TRANSGENIC EPIDERMAL GROWTH-FACTOR RECEPTOR GENE KNOCKOUT MOUSE

Purpose: During embryogenesis we have previously shown that urothelium is essential for normal bladder growth and development. Urothelial gr owth may be mediated by peptides of the epidermal growth factor family , since the epidermal growth factor receptor is expressed in bladder u rothelium and epidermal growth factor has been shown to induce deoxyri bonucleic acid synthesis and migration of urothelial cells in vitro, B ladders from transgenic mice in which the epidermal growth factor rece ptor gene has been knocked out were used to examine the possible role of epidermal growth factor in bladder growth and development, detrusor neoformation and bladder regeneration. Materials and Methods: Whole b ladders from transgenic knockout mice 0 to 10 days old were surgically implanted into the ''subdetrusor'' space of adult athymic nude rat ho sts. After 10 days the dome of the host rat bladder was resected with the distal half of the transplanted knockout mouse bladder, Augmentati on cystoplasty was then performed on the host rat bladder using acellu lar tissue matrix with a portion of the acellular matrix sutured direc tly to the transplanted knockout mouse bladder; The animals were sacri ficed 2 or 3 weeks postoperatively. To test the ability of knockout bl adder tissue to regenerate into the transplanted matrix species specif ic Hoechst dye was used to determine whether the cells within the acel lular matrix were of host (rat) or transplant (knockout mouse) origin, Immunocytochemical analysis was used to assess muscle neoformation. C ontrols consisted of wild-type mouse bladders from the same litter. Si nce epidermal growth factor receptor knockout mice usually die in the neonatal period, the role of the epidermal growth factor receptor sign aling pathway in long-term muscle development was evaluated by transpl anting knockout and wild-type control bladders under the renal capsule of athymic nude mouse hosts. These mice were sacrificed 30 days later and muscle development was assessed using immunocytochemical analysis . Results: Histologically the transplanted acellular tissue matrix in the experimental and control animals appeared the same, containing wel l differentiated urothelial and smooth muscle cells that had migrated into the transplanted matrix. Staining with species specific Hoechst d ye revealed that urothelial and smooth muscle cells transplanted from the knockout and wild-type mouse bladders invaded and regenerated in t he transplanted matrix. There was no apparent difference in the amount of knockout or control mouse tissue in the transplanted matrix. Also, the long-term renal capsule transplants revealed no difference in the amount of smooth muscle in the epidermal growth factor receptor knock out and wild-type bladders. Conclusions: Signaling through the epiderm al growth factor receptor pathway is not necessary for normal bladder development or bladder regeneration after injury.