PARENCHIMA TESTIS IN ONTOGENESIS
BY RADU LIVIU
INTRODUCTION The formation of the contort seminiferous tubules (tubulus seminifer contortus) is multi factorial dependent: first of all it is dependent on the tissue interrelations that determine the phonotype transformations of the primordial structures and second, by the genetic induction factors. The existence of a time and space interval between the genesis of the testis structures and its functional debut imposes the knowledge of the proliferation, migration and assembly processes undergone by the primordial cell populations while changing into structural precursors. Although there have been 159 years since the discovery of the “interstitial endocrine cell” (Endocrinocytus interstitialis) by Franz Leydig (1850) and 144 years since the description of the “support cells” for the spermatogenetic cells (Epitheliocytes sustenans) by Enrico Sertoli (1865), there still are many questions about the genesis of the contort seminiferous tubules precursors: 1. What are the consequences of the germinal cell primordial migration inside the gonad crest? 2. What are the determinants factors of the phenotype transformation undergone by the celomic epithelium from the anterior an internal margin of the mesonephros body? 3. Why are the “primordial germinal cells” visible inside the lecitocel wall only at the three weeks embryo, at quite a distance from the definitive locations – gonad crest? 4. Why the sexual anatomic characteristics appear only after the seventh week of the embryo ante partum life, although the genetic sex is determined during fecundation? 5. What are and how do the “primitive sexual cords” form? 6. When and how do the Leydig interstitial cells form? Are they perennial structures or they have a biphasic evolution? 7. When and how the Sertoli cells form and what is their contribution to “testis cords”? 8. Why do the “testis cords” become “seminiferous tubules” only after puberty? The purpose of this paper is the knowledge of the sexual (testis) cords distribution and of their relations to the mesenchym derived from mesonephros inside gonad crest during their evolution dynamics. The objectives of the paper are bound to the evaluation of the sexual cords structural stages, to the topographic differentiation of the Leydig interstitial cells and to the mesenchym role in straight tubules (rete testis) networking.
MATERIALS AND METHODS Our study has been accomplished on two human embryos aged five and seven weeks respectively, and on four human fetuses aged 12, 16, 24 and 32 weeks. The embryos were completely embedded in paraffin and sectioned along the transverse plane. The testis harvested from fetuses were embedded in paraffin and sectioned along the frontal plane.
RESULTS The analysis of the serried sections made through the five weeks embryo allowed us to evaluate the location and the relations of the gonad crest to the mesonephros and embryo celom (Figure no. 1, A). The micro anatomic study of the fetus testis was achieved on organs harvested from fetuses aged 12, 16, 24 and 32 weeks. At the organ periphery we identified the albuginea tunic and the testis septa (septula testis) that determine compartments inside the medullar of the gonad crest (Figures no. 1C, 2A). When examining with the 10x and 20x objectives we easily identified the sexual cords and their stereo distribution relations to the mesonephros mesenchym migrated inside gonad crest (Figures no. 2 B- D). The sexual (testis) cords have curve trajects and are C, V, U, S, A shaped (Figures no. 2B and 2C). When examining by 20x and 40x one can notice the sexual cords structure: germinal cells, Sertoli cells and lamina limitans (Figures no. 3A-E). Mesenchym around sexual cords forms the “interstitius testis” tat contains Leydig cells (Endocrinolocytus interstitialis) (Figure no. 3G). On the intern side of the testis gonad medullar part, there are rectangular sexual cords (Figure no. 4).
DISCUSSIONS There is a time and space interval between the anatomic evolution of the testis structures and their functional debut. This process is determined by the migration and/or differentiation of the cell populations implemented in the genesis of the seminiferous tubules precursors and of the interstitial connective tissue. The primitive sexual cords develop by the participation of the mesonephros and celomic epithelium cells that migrate to the gonad crest. They are made of sustaining cells that surround completely the germinal cells. The gonad crest that contains mesonephros mesenchym and the primitive sexual cords have two regions: cortical and medullar. After the sixth week of ante partum embryo life the evolution of the gonad crest depends on the embryo sex. There are two factors that determine the sex: TDF (testis determining factor) and SRy (the region on the y chromosome that determines sex). Since the seventh week the cells inside the primitive sexual cords, originating from celom, differentiates only to Sertoli cells (Epitheliocytus sustenans) containing SRy and producing TDF (testis determining factor). The differentiating Sertoli cells organize and form testis sexual cords that also contain germinal cells (Cellulae spermatogenice). At puberty the testis sexual cords get a lumen and differentiate to seminiferous tubules (Tubulus seminifer convolutes et rectus). The mechanism by which the Sertoli cells precursors contact the germinal cells is not elucidated. It is admitted that the relations between the Sertoli cells and primordial germinal cells play an important role in the male sexual cell development. In this way the new mitosis are inhibited until puberty. Equally the Sertoli cells synthesize the anti muller hormone (AMH) that determines the regression of the para mesonephros ducts in male and probably induces the differentiation of Leydig cells from mesenchym. The testosterone secretion by Leydig cells ante partum is controlled initially by the chorionic gonadtrophin secreted by placenta and afterwards by the pituitary gonadtrophins. Another characteristic of the male gonad in humans and mammals is the existence of two Leydig cells generations: the first appears ante partum and is implicated in morph genesis and the second appears at puberty and plays a role in the development and sexual maturing of the individual. The secret of testis development is bound to the synergic gene interaction: SRy, SOX9, WT1 (Wilms’ tumor 1 gene) and the genes for the nuclear receptors (Dax1 and SF1). Testosterone has an important effect on the nervous system. It is considered that testosterone represent a necessary condition of the male sexual orientation as part of the psychosocial behavior. In the absence of testosterone or in the presence of an inactive testosterone by androgen receptor anomaly, the subject presents a feminine psychic orientation. Most of genetic anomalies appeared during sexual differentiation express by a discrepancy between the genetic sex and the phenotype sex. In sexual development pathology there are gonad abnormal geneses at male as well as at female. The most frequent chromosome anomalies in men are: Klinefelter syndrome (abnormal genesis of seminiferous tubules) and the XX man that has hyaline seminiferous tubules, loss of germinal elements and Leydig cells hyperplasia.
CONCLUSIONS 1. Sexual (testis) cords are structures generated by the interactions between the Sertoli cells derived from celom and the germinal stem cells migrated from the gonad crest mesenchym of mesonephros origin. 2. The phenotype transformation of sexual (testis) cords in contort seminiferous tubules takes place at puberty when tubule lumen and spermatozoid differentiation appear. 3. Gonad compartments such as lobules appear after testis septa organization by mesonephros mesenchym differentiation. 4. Leydig interstitial cells differentiate from mesenchym cells probably by Sertoli cells induction and under gonadtrophin control. 5. The knowledge of the male gonad structural particularities during ontogenesis is important in medico-legal anthropology.
Figure no. 1 A. Location and relations of gonad crest at 5 weeks embryo. B. Sexual (testis) cords relations to the mesenchym originated from mesonephros and the differentiation of albuginea at a 12 weeks human fetus. C. Compartments inside gonad crest medulla after the appearance of testis septa and the evolution of mesenchym relations to sexual cords (16 weeks human fetus). 1. Crista mesonefrica; 2. Crista gonadalis; 3. Cavitas peritonealis; 4. Chordae sexuales; 5. Mesenchyma; 6. Albuginea testis; 7. Septula testis. Hematoxiline Eosin stain, Oc. 7
Figure no. 2. A. Sexual (testis) cords groups delimited by primordial septa (24 weeks human fetus). B, C. Sexual cords have variable curve trajects and are implemented in mesonephros mesenchym. D. Rectangular sexual cords deep inside testis medulla region. 1. Septula testis; 2. Chordae sexuales; 3. Mesenchyma; 4. Rectangular sexual cords. Hematoxiline Eosine stain
Figure no. 3. Stages of structural evolution of the testis sexual cords and their relations to mesonephros mesenchym. 1. Cellulae germinalis; 2. Epitheliocytus sustenans; 3. Lamina limitans; 4. Cellulae spaematogenicae; 5. Chordae sexuales; 6. Interstitium testis; 7. Endocrinocytus interstitialis. Hematoxiline Eosine stain
Figure no. 4. Genesis and evolution of the rectangular sexual cords in the medial testis medulla region. Hematoxiline Eosine stain
Bibliography 1. LeMoigne A., Biologie du development, Ed. Masson, Paris, 1995. 2. Pansky B., Embryologie humaine, Ed. Ellipses, Paris, 1986. 3. Hamilton, Boyd and Mossman’s, Human embryology, Ed. Williams and Wilkins Company, Baltimore, 1972. 4. Aslan R.A., Kogan A.B., Gondos B., Testicular development, p. 1950-1955. In: Fetal and Neonatal Physiology, Ed. Plon A.R., Fox W.W., Abman H.S., Ed Saunders 2004