# Histogenesis of the Uterine Horn in the Domestic Cat (Felis silvestris catus): LM, TEM, and SEM Study

## TL;DR

This study examines how the uterine horns in domestic cats develop before birth, using advanced microscopy techniques to track tissue changes from early to late pregnancy.

## Contribution

The study provides a detailed histological timeline of uterine horn development in cats, revealing when key structures like the endometrium and myometrium begin to form.

## Key findings

- Tissue differentiation in the uterine wall begins around day 33 of gestation in domestic cats.
- The endometrium and myometrium start forming between 42 and 51 days post-conception and continue developing until birth.
- Full maturation of the uterine wall, including gland development and epithelial remodeling, occurs after birth.

## Abstract

This study investigates the prenatal development of the domestic cat’s uterine horns, originating from the paramesonephric (Müllerian) ducts. The aim was to describe the histodifferentiation of the uterine wall, focusing on the structural advancement of the endometrium and myometrium at birth. This study analyzed 60 fetal specimens aged 28–63 days post-conception using light, scanning, and transmission electron microscopy. Research has shown that tissue differentiation in the wall of the domestic cat’s uterine horns begins in the mid-prenatal period, i.e., around day 33 of gestation. The formation of the endometrium and myometrium in the uterine horns begins slightly later, i.e., between 42 and 51 days post-conception, and continues until the end of pregnancy. By birth, the uterine wall possesses all the layers found in adults, though full maturation, including gland development and epithelial remodeling, occurs postnatally. These findings provide critical insights into feline reproductive physiology and have broader implications for comparative embryology and veterinary diagnostics. Given the domestic cat’s significance in human society, understanding its reproductive development enhances veterinary care and supports future research on developmental disorders across species.

This study employs light microscopy, scanning electron microscopy, and transmission electron microscopy to describe the morphological changes occurring during the development of the domestic cat’s uterine horns, originating from the uterine segments of paramesonephric ducts (uPD). Comprehensive observations conducted on 60 specimens aged 28–63 days post-conception (p.c.) revealed that the formation of the endometrium and myometrium in the uterine horns begins around day 33 p.c., initiated by mesenchymal differentiation. During endometrial development, fibroblasts align first in perpendicular and then in oblique columns. The subdivision of the lamina propria into basal and functional layers becomes evident shortly before birth, with the functional layer remaining flat until the end of the prenatal period. The endometrial epithelium transforms from a simple columnar to a pseudostratified structure, undulating by day 63 p.c. Myometrial formation commences with the differentiation of myoblasts, which are arranged in a circular pattern. By the end of gestation, these myoblasts differentiate into smooth muscle cells, organizing into distinct inner circular and outer longitudinal sublayers. Although the fundamental layered architecture of the uterine wall is established before birth, its full maturation—including gland formation, epithelial transformation, and further development of the myometrium—continues postnatally.