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STRUCTURAL STUDY OF THE DIFFERENTIATION Ahmed Mohammed. Sulaiman 1*and Mahjop Ezendah 2. 1 Anatomy, and 2 Physiology Departments, Faculty of Medicine, University of Tripoli/ Tripoli Libya. ـــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ ABSTRACT BACKGROUND: Development of foregut is still controversy, both and , are taking origin from the cephalic part of foregut. AIM OF THE WORK: To study formation of anterior part of digestive system has been studied in an animal model, which allowing more specimens at different stages to be examined. In this study we have focused on development of the most cephalic part of the foregut, as it is a place of many congenital anomalies. MATERIAL AND METHODS: In this study CBA inbred strain mouse embryo has been used, particular attention was directed to the embryo ages 9.5 to 11 days. Males were introduced to female’s cages at 12.00 noon and removed at 4.00 Pm, then females which shows vaginal plugs were regarded as pregnant and were isolated, and that day regarded as (day 0) of embryonic development starting from 2.00 pm. The pregnant uterus was dissected and embryos examined for staging using Theiler staging [1] as a reference, and embryos processed for . RESULTS: In Theiler stage 14 (9 d.p.c), the epithelial lining of the ventral aspect of foregut just below the 4th pharyngeal pouch, is thickened and form a multicellular, but the dorsal aspect is thin and formed of one cell layer. In Theiler stage 15 (9.5 d.p.c), at the same area, the main even is the appearance of the respiratory primordium. At stage 16 (10 d.p.c), trachio-esophageal sulcus is formed, and at Theiler stage 17 there were a complete fusion of the two endodermal ridges and separation of foregut into trachea anterior and esophagus posterior. CONCLUSION: In our view, the endodermal ridges which occur as a result of proliferation of the epithelial lining of the laryngotracheal sulcus play a fundamental role in the process of foregut separation and its normal development into oesophagus and trachea, and there was no place for the concept of ascending tracheo- oesophageal septum. KEYWORDS: Foregut, Esophagus, Trachea, septum, sulcus, pharyngeal pouch. * Corresponding author: Dr Ahmed M. Sulaiman, Anatomy and department, Faculty of Medicine, University of Tripoli, Tripoli, Libya. Email. [email protected]. Mobile: 00218926628237 INTRODUCTION and the foregut represents what is called the The most cephalic part of foregut formed tracheo-esophageal septum[7, 10 ]. as a result of cephalocaudal and lateral folding Two longitudinal ridges formed of the embryo, which will differentiate and give tracheoesophageal ridges these ridges then fuse rise the many structures such as esophagus and and separates the primitive foregut into trachea trachea, and stomach [2, 3] , the ventrally and esophagus dorsally [11] . The lung differentiation of this part of gut, is very bud is soon divided into right and left , complicated and still there is no clear picture during this process many factors are involved about the mechanism involved, despite many including transforming growth factor-beta attempts to resolve this (TGFβ), Osr1, which will regulate the branching [ u, 5] . process [12, 13, 14] and Bmp 4, SOX2, noggin As early as the fourth week in ,play essential roles in the separation of the development, the esophagus of the human esophagus from neighboring respiratory embryo is merely a sphincter or constricted part system[15] , the upper end of the sulcus remains of the primitive foregut between the pharynx fixed at the level of the first cervical vertebrae, and stomach [6] . smooth muscle and vascular endothelium The epithelial lining of this part of the gut actively differentiate from mesenchymal shows clear evidence of high mitotic activity, progenitors during lung and esophagus very early in development [7, 8] especially its development [16], other Study performed in ventral aspect, which will differentiate to give chicken embryos show, no evidence for lateral rise to certain structures including the thyroid, foregut ridges inside the undivided foregut[17], , esophagus, and lung bud. and the formation of the early lung bud as well The development of esophagus started as an as the process of separation of trachea and outgrowth from the ventral wall of the foreguts esophagus remains unclear and the true [9],when it expand caudally the mesenchymal embryologic investigations are extremely rare in tissue trapped between the descending lung bud this field. 66 | P a g e

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Over all theories can be divided into four main pharyngeal pouch still few Cells thick on ventral groups [ 18 ] , intraembryonic pressure; aspect. (Star) x 280 mag. epithelial occlusion; differential growth; and vascular occlusion, based on analysis of anomalous TE development in adriamycin exposed rat embryos theory has been described [18 ] that failure of the tracheal bud to develop normally from the primitive foregut is the main event which leads to the tracheo-esophageal anomalies, As the proximal part of the primitive foregut develops primarily into a trachea rather than an esophagus. MATERIAL AND METHODS In this study CBA inbred strain mouse embryo has been used, particular attention was directed to the embryo ages 9.5 to 10.5 days. The animals were housed at a room temperature Figure 2: Theiler stage 15 (9.5 d.p.c), T.S. just of about 23Cº in cages with food and water below the 4th pharyngeal pouch. Note the supply and artificial lighting, the period of respiratory primordium( Arrow) X 280 Mag. darkness started at 12.00 noon and ended with 15 hours of light. Males were introduced to females cages at 12.00 noon and removed at 4.00 Pm, and females which shows vaginal plugs were regarded as pregnant and were isolated , and that day regarded as ( day0) of embryonic development starting from 2.00 pm. At room temperature , embryos were harvested at different ages, during which the female were killed by carbon dioxide inhalation followed by cervical dislocation, the pregnant uterus was dissected and conceptuses removed to a dish containing fresh Hank’s buffer Figure 3: Midsagittal section at stage 16 (10 solution, then the membranes removed and d.p.c).Note development of trachio-esophageal embryo examined for staging using Theiler sulcus (arrow) x 200 mag. staging system [1] as a reference, and only embryos corresponding to the developmental age were collected for the study, and processed for histology embedded in wax and cut in 7 µm sections , then were stretched on glycerine-albunen precoated slides stained using Haematoxylin and Eosin. RESULTS

Figure u: Theiler stage 17 (10.5 d.p.c).T.S at the cranial end of the trachio-esophageal sulcus. Note the of the two ridges are not completely fused (arrow) oesophageal (g) and trachea (T), note tracheo -esophageal septum (arrow) x 200

Figure 1: Theiler stage 14 (9 d.p.c) At this stage mag. the epithelial lining of the foregut below the 4th

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differentiation and mechanism of separation of the lung bud or mechanism involved in the formation of the bronchial tree and the close proximity of the larynx and lung primordium adds to the complexity and results in another controversy regarding the level of separation of the lung and larynx , Smith et al [ 7 ] , Katharine et al [ 10] , and Marshall [ 19 ] . From this study the first evidence of the lung bud appears at stage 14, which corresponds to 9 days’ post coitus (9 d.p.c), Theiler [1], and this stage corresponding to stage 11 in human, at

Figure 5 : T.S at stage 17 (10.5 d.p.c) at the this stage the lung bud appears in the level of caudal end of tracheo-esophageal form of an epithelial thickening on the ventral sulcus. Note the complete fusion of the two aspect of the foregut (fig.1), and this finding endodermal ridges (arrow) x 200 mag. agrees with Zaw-Tun [11], Sanduo et al [ 21], Sutliff et al [22] and O’Rahilly [ 23] in this study we found that endodermal ridges on the inside lateral wall of the primitive foregut involved in the process of foregut separation, and as these ridges increase in size they eventually meet in Midsagittal plane with agreement with Smith et al [ 7 ] . The epithelial lamina results from proliferation of the epithelium which lines the lateral wall of the laryngeal sulcus in agreement with Sanduo et al [ 9 ] , and not as a result of a pressure exerted by the arytenoid selling on the wall of the laryngeal sulcus as maintained by Zaw-Tun et al [ 11] and O’Rahilly et al [ 23, ] sever Figure 6: T.S at stage 18 (11 d.p.c) T.S below narrowing of the esophageal lumen occurred at the tracheo-esophageal sulcus. Note complete the level of tracheal bifurcation fig .7 in separation of the foregut into esophagus (g) , agreement with the finding of most other and trachea (B) X200 mag. studies, and at this point the trachea and esophagus are very close to each other, but there was no evidence of complete occlusion of the esophagus lumen at any of the stages studied. CONCLUSION This study, demonstrated that as early as nine days post coitus (9 d.p.c), stage 14 in mice which corresponding to stage 11 in endodermal ridges appears on the inside lateral wall of foregut, these epithelial ridges showed increase in mitotic activity, till they meet in mid-sagittal plane at stage 18 ( 11 d.p.c) Mesenchymal tissue located between the cephalic part of foregut and newly formed lung diverticulum, Figure 7: stage 18 (11 d.p.c) T.S at level of the marks the point where the endodermal ridges carina(arrow), note the two broncho-pulmonary started to fuse in the process of dividing the buds (B) and narrowed esophagus (star) x 200 cephalic part of foregut into esophagus mag. posteriorly and trachea anterior. DISCUSSION REFERENCES As for more than three centuries there was [1] Theiler K. The mouse, development and agreement that the lung bud originated from the normal stages from fertilization to u weeks of ventral aspect of the foregut] Metzger et al [u] age. 1972. Springer-Verlag, Berlin. , Smith et al [ 7 ] , and Zaw-Tun et al [ 11] but [2] Williams AK, Quan QB, Beasley SW. there was no agreement regarding its further Three-dimensional imaging clarifies the process 68 | P a g e

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of tracheoesophageal separation in the rat. J noggin and Bmps. Differentiation. 2006; Pediatr Surg. 2003; 38(2):173-7. 74(7):422-37. [3] Fausett SR, Klingensmith J. [16] Kumar ME, Bogard PE, Espinoza FH, Compartmentalization of the foregut tube: Menke DB, Kingsley DM, Krasnow MA. developmental origins of the trachea and Mesenchymal cells. Defining a mesenchymal esophagus. Wiley Interdiscip Rev Dev Biol. progenitor niche at single-cell resolution. 2012 Mar-Apr; 1(2):184-202. Science. 2014; 346 (6211):1258810. [4] Metzger R, Wachowiak R, Kluth D. [17] Metzger R, Wachowiak R, Kluth D. Embryology of the early foregut. Pediatr Surg. Embryology of the early foregut. Semin Pediatr 2011 ; 20(3):136-44. Surg. 2011; 20(3):136-44. [5] Kluth, D., Fiegel, H. The embryology of the [18] Merei J, Kotsios C, Hutson JM, Hasthorpe foregut. Semin Pediatr Surg. 2003: 3-9. S. Histopathological study of esophageal atresia [6] O’Rahilly, R. and Muller, F. Respiratory and tracheoesophageal fistula in an animal and alimentary relations in staged human model. Pediatr Surg. 1997; 32(1):12-14. embryos. New embryological data and [19] Marshall Flint, J.): The development of the congenital anomalies. . 1906; Am. J. Anat., 6: 1–137. Ann.Otol.Rhinol.Laryngol. [20] Smith, E.L. The early development of 1984; 93:421-429. trachea and esophagus in relation to atresia of [7] Smith, E.L. The early development of the the esophagus and tracheoesophageal fistula. trachea and esophagus in relation to atresia of 1957; Contr. Embryol.36:41-57. esophagus and tracheoesophageal fistula. [21] Sanduo, J.R and Mateu, J.M.D. The Contr.Embryol. 1957; 36:41-57. laryngeal primordium and epithelial lamina. A [8] Sutliff, K.S and Hutchins, G.M. Septation new interpretation. 1990; J. Anat. 171:207-222. of the respiratory and digestive tracts in human [22] Sutliff, K.S. and Hutchins, G.M. Separation embryos: Crucial role of the tracheo- of respiratory and digestive tracts in human oesophageal sulcus. Anat. Rec. 1994; (23): 237- embryos: Crucial role of tracheo-esophageal 248. sulcus. 1994; Ana. Rec.238: 237-248. [9] Sanduo, J.R and Mateu, J.M.D. The [23] O’Rahilly, R. and Muller, F. laryngeal primordium and epithelial lamina. A Developmental staged in human embryos. 1987; new interpretation. J. Anat. 1990; 171: 207-222. Carnegie, Inst. Wash. Publication.637. [10] Katharine S. Sutliff, Dr. Grover M. Hutchins. Septation of the respiratory and digestive tracts in human embryos, Crucial role of the tracheoesophageal sulcus .Anatomical record. 1994; 238 (2): 237–247. [11] Zaw-Tun, H.A. The tracheo-oesophageal septum fact or fantasy? Origin and development of the respiratory primordium and esophagus. Acta Anat.1982; 114: 1-21. [12] Serra, R, Relton, Pelton, R.W. and Moses, H.L TGFβ1 inhibits branching morphogenesis and Nmyc expression in lung bud organ cultures. Development .1994; 120(8): 2153-61. [13] Bellusci S, Grindley J, Emoto H, Itoh N, Hogan BL. 10 (FGF10) and branching morphogenesis in the embryonic mouse lung. Development. 1997; 124(23):4867- 78. [14] Han L , Xu J , Grigg E , Slack M , Chaturvedi P , Jiang R , Zorn AM. Osr1 functions downstream of Hedgehog pathway to regulate foregut development. Dev Biol. 2017; 427(1):72-83. [15] Que J, Choi M, Ziel JW, Klingen smith J, Hogan BL.Morphogenesis of the trachea and esophagus: current players and new roles for

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