Glomerulogenesis and Histomorphometeric in Mus musculus Embryo

In mammals, the kidneys originate in an embryo from the mesoderm through three excretory organs, namely: Pronephros, Mesonephros, and Metanephros. After the formation of Metanephros is completed, the kidneys begin to form nephrogenesis through mesenchymal cells located at the tip of the ureteric bud, that contribute in the formation of glomerulus and Renal tubules. The stages of glomerulus formation in the embryo of albino mice at the age of 14 to 19 days of gestation were studied. It was obtained after the sacrifice of the expectant mother and the kidneys were excised from the embryos and fixed using Aqueous Bouin's solution, Microscopic slices with a thickness of 6 microns were then made in a paraffin method and were photographed by a camera for microscopic imaging. Histological measurements were performed on them using the program IMAGE J program and analyzed statistically using the SPSS program. Results of the current study showed the presence of five stages of glomerulus formation, namely, the renal vesicle, which represents the first stage in the formation of the nephron and glomerulus. This is followed by the Comma shape stage, S-shaped stage, Capillary loop stage and finally the Mature glomerulus. This is surrounded by a capsule, known as Bowman’s capsule being part of the Malpighian or Renal corpuscle. The statistical analysis showed that there were significant differences between the average diameters of the glomerular development stages, and that the mature glomerulus was larger in diameter than the rest of the stages. The study aims to determine the stages of glomerulus formation and histologically measure its diameter in the embryo of a Mus musculus .


Histological study
The results of the current study of the kidney in the Mus musculus embryo showed five stages in the formation of the glomerulus, which are as follows:-

Renal vesicle stage
In the kidney of the Mus musculus embryo at 14 day of gestation, it appears that the mesenchymal cells located at the tip of the ureteric bud transformed into a closed V-shaped structure with a central cavity known as the renal vesicle. It also appears that it is composed of a row of cells with oval nuclei located at the superficial part of the renal cortex (3-1). [11] noted that the formation of a glomerulus requires the occurrence of segmentation and morphological changes in the renal vesicle, which is the first epithelial structure to arise from the mesenchymal cell. Thus, it suffers on its lower side from invagination to form a vascular cleft ( Fig. 3-1). It also represents the primitive form of the glomerulus [12].

Comma shaped stage
In the kidney of the Albino mice embryo, a comma-like shape appeared. This represents the second stage of the formation of the glomerulus, which arises from the invagination of the renal vesicle and is divided into two regions: the proximal and distal segment, between which the vascular cleft lies. This corresponds to what was found [13]. This form consists of Parietal cells [14] Figure (3-2).

S-Shaped stage
At this stage, the shape of the glomerulus in the kidney of the Mus musculus embryo was in the form of a letter S-shape (3-3) consisting of three segment, an upper called the proximal segment, located near the capsule, lined with columnar tissue, and a lower representing the distal segment lined with cuboidal tissue between them located Median curve. [11] confirmed in his study that the three segments play an important role in the formation of the glomerulus and renal tubule. He found the parietal layer of Bowman's capsule and the visceral epithelium arise from the Proximal segment (upper segment), while the proximal tubule, the Henle loop and the distal tubule, arise from Median segment. As for the distal segment(Lower), it connects the renal tubules to the collecting tubule. At this stage, cells begin to migrate to a vascular cleft called the endothelial cell, arises from stem cells known as Angioblast, to form glomerular capillaries [15].

Capillary loop stage
In the kidney of the mice embryo, invagination appeared in a letter S shape at its lower segment while its cuboidal cells turned into flat. Then, it appeared in the shape of the letter C. Its edges are lined with flatting cells and it reaches the endothelial cell to form glomerular capillaries to settle in the previously formed vascular cleft (Figure 3-4). [16] indicated in his study that these capillaries undergo rapid changes, including the appearance of the glomerular capillary system, differentiation of the presumptive endothelium cells to Malpighian corpuscle, and the formation of renal arteries and veins.

Mature Glomerulus
The mature glomerulus can be distinguished in the area of the cortex as being surrounded by Bowman's capsule, It is formed of the following two continuous layers of epithelium: an external or parietal layer of Bowman's capsule which is formed of simple squamous epithelium surrounded by reticular fibres and an internal or visceral layer which is adherent to the glomerular blood capillaries the visceral layer of the Bowman's capsule is formed of modified simple squamous cells known as podocytes or glomerular epithelial cells.these cells facilitate the passage of glomerular filtrate to the capsular space ). It appears as being composed of two layers: a parietal layer consisting of squamous epithelium and a layer surrounding the glomerulus known as the visceral layer. While the space between the two layers is called Bowman's space Figure (3)(4)(5). In embryos 18 and 19 day of gestation, the juxtaglomerular apparatus, as well as the macula densa, were observed ( Fig. 3-6). [12] indicated that the first three stages can be observed near the surface of the cortex, while the last two stages can be observed deep in the cortex area. Although the stages of Glomerulogenesis are different, they can be seen in all Mus musculus embryos from the age of 14 to 19 days of gestation. This was confirmed by [17], and it is also consistent with what was stated by [12]. That show the development of kidney in human fetus at 14 week gestation. The results of the statistical analysis showed that there were significant differences in the diameters of the stages of glomerulus development at the significance level of (P≤ 0.05). Table (

Conclusions
The glomerulogenesis considered one of the main developmental processes in the kidney of embryo ,that occur after formation of Metanephros, Mesenchymal cell is contribute in happening that ،This study showing five stage for Development glomerulus represented by Renal vesicle, Comma shape stage, S-shape stage, Capillary loop stage, and finally the mature glomerulus, and make statistical analyze for diameters to every stage, This study explain the important role in glomerulogenesis during the life of the embryo.

Ethical Clearance
Ethics of scientific research were carried out in accordance with the international conditions followed in dealing with laboratory animals, and included animal health, husbandry and care for it, and providing appropriate conditions for it in terms of food, and appropriate methods were  adopted in dealing with it when experimenting, and this is consistent with the instructions of the Iraqi Ministry of Health and Environment.