Peculiarities of morphogenesis of the urinary system of the laboratory mouse

The process of initiation and formation of the urinary system is similar among mammals. Experimental models using the laboratory mouse serve as an effective tool for elucidating the mechanisms of urinary tract development, since analogous studies on human embryos are associated with serious methodological and bioethical limitations. An important region that ensures the functioning of the upper and lower parts of the urinary system is the ureterovesical junction. In the definitive state, it performs the function of a physiological valve that provides unobstructed unidirectional urine passage. The study of its formation is fundamental for understanding the etiology of anomalies in this region. The aim of the study was to determine the main regularities and chronological sequence of prenatal ontogenesis of the ureterovesical junction in the laboratory mouse. The study was performed on 15 series of histological sections of laboratory mouse embryos. The material was obtained from the collection of the Department of Histology, Cytology and Embryology of Bukovinian State Medical University. A complex of morphological research methods was applied (morphometry, microscopy, three-dimensional computer reconstruction, and statistical analysis). In the early stages of mammalian development, the mesonephric (Wolffian) ducts open into the cloaca, which separates into the caudal part of the hindgut and the urogenital sinus, the primordium of the urinary bladder and urethra. This period covers days 10–15 of gestation (stages E10.5–14.5) in the laboratory mouse, corresponding to weeks 4–8 of gestation in humans. The caudal part of the mesonephric duct is the anlage of the upper urinary tract. In the laboratory mouse, at stage E10.5–11.5, the cranial part of the ureteric bud connects with the renal mesenchyme and forms the renal collecting system, whereas the caudal part of the ureteric bud differentiates into the ureter. During E10.5, the ureters connect with the urinary bladder via the common nephric duct. By stage E14.5, the ureters have separated from the mesonephric ducts and fused with the structures of the urinary bladder, in particular with the anlage of Lieutaud's trigone. Thus, the normal architectonics of the intramural segment and ureteral orifice in the laboratory mouse directly depends on coordinated remodeling of the common nephric duct through local apoptosis at stage E11–E13. Differentiation of the ureter from the mesonephric duct and its connection with the urinary bladder in the laboratory mouse are ensured by a sequence of morphological transformations: apoptosis of the common nephric duct at stage E11–E12, fusion of the epithelial layers of the ureter and urinary bladder at stage E13, and accelerated growth of the urogenital sinus during E12–E14. Received: 9.02.2026 | Revised: 1.04.2026 | Accepted: 20.04.2026