There are species differences in the junction between the uterine tube (isthmus) and uterine horn, and the role played by the UTJ is affected by different factors, which greatly vary among mammals. In the present work, the cattle’s UTJ and camel’s UTJP were investigated by histological and histomorphometric examination as a fundamental knowledge for further biotechnological and clinical application. This study indicated that the morphology and histology within the cattle’s UTJ and camel’s UTJP differ depending on their functions.
In the present work, the UTJP exists in camels and is completely absent in cattle. Similarly, UTJP was previously reported in dromedary camel5,12-14. However, the details regarding its morphology and morphometry are lacking. Dromedary camel’s UTJP has a conical shape directed from the base of the oviduct toward the uterine lumine, it has a pale yellowish color, 0.5± 0.2 cm height, and 0.3±0.1 cm width. The luminal area, luminal epithelial density, and the thickness of tunica muscularis is higher in camel UTJP than that of cattle UTJ. Moreover, camels UTJP possess a higher number of uterine folds, high folds height, higher epithelium height, and higher fold area compared to cattle UTJ. This unique feature is attributed to the formation of primary, secondary, and occasionally tertiary folds. This difference compared with other mammals could be related to the regional function. In the dromedary camel, the function of the uterotubal junction papilla is lacking.
Furthermore, in cattle’s UTJ, the mucosa consists of primary folds lined with ciliated and non-ciliated simple columnar epithelium, and the submucosa enriched with simple tubular glands open directly into the lumen. These results are consistent with that previously reported in cattle21. Several species indicate increased ciliogenesis under the influence of estradiol22, and non-ciliated cells may have the ability to transform into ciliated cells following estradiol treatment23. Whereas, in the dromedary camel’s UTJP, the mucosa consists of primary, secondary, and tertiary folds lined with ciliated and non-ciliated pseudostratified columnar epithelium, and the submucosa showed no endometrial glands. Similarly, the uterotubal junction in camel is lined by ciliated and non-ciliated pseudostratified columnar epithelium14. In contrast, the oviduct of the camel is lined by ciliated and non-ciliated columnar epithelium13. This variation could be related to regional differences in the or the reproductive status of the camels. Camels are induced ovulatory and follicular waves continue to develop during the breeding season. The height of the lining epithelium increased during the follicular wave in response to the high serum concentrations of estradiol1. High estrogen levels caused an increase in cellular proliferation, uterine epithelial cell secretion, uterine blood flow, and endometrial vascular permeability24.
In addition, in cattle’s UTJ, the tunica muscularis is thin and consists of inner circular and outer longitudinal muscles. While, in the dromedary camel, the tunica muscularis is nearly double the thickness of that of cattle and consists of inner circular and outer longitudinal muscles. The significance of the absence of uterine glands and the thick tunica muscularis of the camel’s UTJP is unknown. The varying thickness of the tunica muscularis between the two species suggests that it is related to the function of this region. Contractions of the tunica muscularis may cause stenosis of the utero-tubal junction resulting in restriction and regulation of the sperm passage towards the isthmus; or descent of oocyte and fertilized zygote to the uterus25. Furthermore, the thick tunica muscularis might serve to provide the peristaltic and anti-peristaltic waves in the isthmus. Peristaltic contractions of these thick muscles together with the movement of the cilia could help in the passage of the early embryo toward the uterus26. Therefore, the thick tunica muscularis camel’s UTJP might play a role in regulating the passage of sperm from the uterus to the oviduct. In addition, it could play a role in the hatching of blastocyst before it descends from the isthmus into the uterine lumine. In Llama, the hatching of the blastocyst in the oviduct is mandatory before they descend to continue to develop in the uterus6. Therefore, the morphological, histological, and morphometric characteristics of the camel’s UTJP might play a significant role in selecting sperm before passage to the oviduct for fertilization, and hatching of the blastocyst might be a mechanical process that occurred during the passage of the blastocyst through the UTJP in dromedary camel.
Furthermore, in this work, in cattle, there were plenty of superficial (SG) and deep uterine glands (DG). The epithelium height, perimeter, and area of SG were significantly higher than DG. However, the density of DG was higher than SG. This increase in superficial endometrial glands might occur due to the reduction in uterine edema of the subepithelial connective tissue layer. Similar results were recorded in buffalo27. In mammals, the UTJ acts as a reservoir for sperm storage in the preovulatory phase because it contains abundant uterine glands. After mating the sperm enters the uterus and aggregate at the terminals of the uterine horns, which clump together and adhere to the ciliated epithelium in the dog to conserve energy until ovulation and the ova entering the ampulla28. Passage of motile sperm through the UTJ is regulated by both the physical constraints of the UTJ opening, resulting in only a privileged population of sperm, and molecular screening of the sperm28,29. The ciliated epithelium of the UTJ has the capability of screening the proteins on the acrosome of the sperm and allowing the passage of selected sperm29. In contrast, the total number of superficial and deep endometrial glands in cows was unchanged between the estrous cycle, but the area of the subepithelial connective tissue layer enlarged at the follicular phase30. In our case, the samples were collected with unknown reproductive history, but it seems that it collected from cyclic animals during the follicular phase of the estrous cycle. In addition, the absence of uterine glands in camel’s UTJP requires further studies on the mechanism of sperm storage before ovulation and screening the different parts of the uterus to localize the area of sperm storage.
In conclusion, this study revealed several interesting morphological and histological features of the camel’s UTJP such as the epithelial lining, absence of glands, and the presence of a thick layer of tunica muscularis might indicate that this part of the oviduct plays a mechanical process in selecting spermatozoa and assisting of blastocyst hatching during their passage through it.
In Conclusion: Camel UTJP is a specialized structure found at the UTJ, several interesting morphological and histological features of the camel UTJP such as the epithelial lining, absence of uterine glands, and the thick tunica muscularis might indicate that this part of the oviduct plays mechanical process in selecting spermatozoa and assist of blastocyst hatching during their passage through it. Further research is needed to fully understand the molecular mechanisms underlying the papillae function, which could have important implications for improving reproduction in camels.