J Multi Dent Res. 2022;8(2):57–60 Journal of Multidisciplinary Dental Research Original Article Morphological Study on Development of Vascular Endothelium in Chick Embryo Yaiko Hara 1, ∗ 1 Department of Anatomy, Tsurumi University School of Dental Medicine, 2-1-3 Tsurumi-ku, 230-8501, Yokohama, Japan ARTICLE INFO Article history: Received 05.07.2022 Accepted 28.07.2022 Published 27.12.2022 ∗ Corresponding author. Yaiko Hara hara-yaiko@tsurumi-u.ac.jp https://doi.org/ 10.38138/JMDR/v8i2.22.29 ABSTRACT Te vascular endothelium and hematopoietic stem cells are believed to derive from common progenitor cells called hemangioblasts. However, morphological study on the development of vascular endothelial cell has been scarce. Te present study is intended to provide more morphological explanation of the diferentiation process of the hemangioblast. We performed histological observation, using 10 four-day-old chick embryos. Afer fxation with 4% concentration paraformaldehyde, hematoxylin eosin staining, toluidine blue staining and immunostaining were performed in that order for observation of morphological changes of the detected cells. Blood corpuscles were aggregated in the dorsal aorta and the heart (that had been observed to beat in its preparation). Some red blood cells showed immunoreactivity to both anti-Flk-1(VEGFR2) and anti- CD31 antibody. Additionally, some blood cells had small vacuoles in the cytoplasm, and they fused to form one larger vacuole ultimately a balloon-like shape that was connected to endothelial cells. Tese cells were present in close proximity to the vascular endothelium. We reveal that some of the early embryonic blood cells diferentiate into vascular endothelial cells. Keywords: Vasculogenesis; Angiogenesis; Hemangioblasts; Vascular endothelial cells 1 INTRODUCTION Tere have been a lot of studies about the development of vascular endothelium (1–3) , and vasculogenesis and angio- genesis are two commonly known developmental processes. Angiogeneisis is known to be a process of sprouting of new capillaries from pre-existing blood vessels while vasculoge- nesis is a process of de novo formation of primitive vascular networks by diferentiation, expansion (4,5) , and coalescence. Vasculogenesis is also known to be involved in angiogenesis during the progression of periodontal disease (6) and tumor growth (7,8) , but their detailed morphological study has been scarce. Both mechanisms might establish the rapid development of the blood circulating system in early embryonic stage. Tere is increasing evidence that hematopoietic cells and endothelial cells might be derived from the common pre- cursor cells which is called hemangioblasts (9) . It is thought that the hemangioblasts are derived from mesodermal cells and that they diferentiate into blood-cell lineages or the endothelial cells (10) . However, it is morphologically not clear how the hemangioblast diferentiates into the vascular endothelial cell. Our previous histological study (11) reported that some blood corpuscles diferentiate into endocardial endothelial cells. Te endocardial endothelium is a monolayer of epithelium that is continuous to the vascular endothelium. Terefore, the formation of vascular endothelium and heart endocardium is believed to follow the same developmental process (12,13) and more morphological explanation is needed concerning this diferentiation process. Here we report histological analysis of how the red blood cells change their form to vascular endothelial cells. 2 MATERIALS AND METHODS In this study, twenty fertilized eggs were used. According to Hamburger and Hamilton stages (14) , white leghorn chick embryos staged 4 were incubated at 38 ◦ C under 80% humidity. Te embryos were explanted from yolk sac together with surrounding area vasculosa and whole bodies were fxed with 4% paraformaldehyde solution for both light-microscopic and electron-microscopic observations. Our experiments were approved by the Ethical Committee © 2022 Published by International Dental Educationists’ Association (IDEA). Tis is an open access article under the CC BY license (https://creativecommons.org/licenses/by/4.0/) 57