Morphogenesis of the uterine tube in the European shorthair cat in the prenatal and postnatal period: Light microscopy and three- dimensional reconstruction study

The study aimed to describe the morphogenesis of the domestic cat uterine tube, from the primordial tubal segment of the paramesonephric duct (TsPD) to the mature organ. The specific aims included identifying differences in the rate and way of development of the layers in the wall of the infundibulum, the ampulla, and the isthmus. In the study we conducted light microscopic (LM) observations of the uterine tube wall, and analysis of 3D models, which were used for the first time to visualize the arrangement of the paramesonephric duct and highlight the pattern of the developing mucosal folds. The results revealed the two stages in the prenatal development of the domestic cat uterine tube. The first stage lasts from day 26-44 p.c. (post-conception) and includes the growth of the TsPD. It starts with formation of the TsPD's epithelial tubule in the mesenchyme of the anterior part of the mesonephros. The tubule, surrounded by mesenchyme, elongates posteriorly, and the TsPD can be divided into three sec-tions according to their location and diameter, i.e., anterior, middle, and posterior. The first stage ends with the histodifferentiation of the mesenchyme into loose connective tissue and mucosa formation. The second stage lasts from approximately day 45-63 p.c. and comprises the formation of the proper layers in the uterine tube wall. The pace and pattern of layers' development are specific to each section of the uterine tube, as tissues first differentiate in its anterior part and then continue posteriorly. The mucosal folds appear after day 44 p.c. in the infundibulum, and they become long and branched by the end of the prenatal period. Then, approximately day 48 p.c., the single mucosal folds appear in the ampulla, and at the end, i.e., about day 63 p.c., they become visible in the isthmus. The 3D models revealed the unique spiral-shaped arrangement of the mucosal folds in the ampulla. The tunica muscularis starts to develop ca day 48-51 p.c. in the anterior part of the uterine tube. On approximately day 55 p.c., the circular muscle layer can be distinguished in the ampulla, while in the isthmus, it develops just before birth. The postnatal development of the infundibulum includes the formation of the labyrinth-like system of mucosal folds, whereas in the ampulla and isthmus, branched mucosal folds and the second longitudinal muscle layer develop postnatally. At the end of the prenatal period, the differences in the wall thickness between the individual segments of the uterine tube reflect the proper proportions of the uterine tube wall in the mature female.(c) 2022 The Authors. Published by Elsevier Inc. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).