Histol Histopathol (1999) 14: 991 -1000 Histology and 001 : 10.14670/HH-14.991 Histopathology http://www.hh.um.es From Cell Biology to Tissue Engineering Invited Review The prepubertal testis: a quiescent or a silently active organ? R.Rey Endocrin e Research Un it (CEDIE-CONICET), R. Gutierrez Children Hospital, Buenos Aires, Argentina Summary. T he develo pme nt of the testi s is play an essential role in th e development of th e other characterised by dramatic changes between birth and popul at ion, th e germ cel\s, fro m which the spermatozoa adulthood. The most conspicuous changes take pl ace arise. The interstitia l ti ssue contains a testi s-specific during puberty, when the semin iferous tubule diameter component, the Leydig cel\s which produce androgens, increases sig nificantl y owing to an important proli­ a nd a no n-s pecif ic o ne, ma inl y re prese nted by fera tion of germ cells, giving rise to sperm atozoa, and to connecti ve tissue. The two testicular compartments are the development of a tubular lumen; in the interstitial functionall y interdependent: androgens are essential fo r tissue characteristic Leydig cells appear and secrete high Serto li cell matu ratio n and for spermatogenesis, and levels of testosterone. T hese pubertal changes of the Leydig cell development and functi on are modul ated by testis can be detected clinicall y since th ey result in seminiferous tubule-secreted factors. testi cul ar volume and serum and rogen level increments. The development of the testes, from the time of their The pre pubert al testis has c1assical\ y been defined as a di ffe re n t ia ti o n in th e foe tus until adulthood , is quiescent organ. However, since adequate stereological characteri sed by dramatic morphological and functional methods fo r mi croscopic analysis are available, it has c ha nges. These c ha nges w iII be bri e fl y descri bed been shown that the male gonad triplicates its volume hereafter as an introductio n to the discussion of one be tween birth and the onset of puberty. Sertoli cells and particular peri od of the postnatal development of the sperm atogoni a proli ferate intensely; this is critical fo r male gonad: the prepubertal period. th e developme nt of qu a n titat ive ly no rma l adult sperm atogenesis. Semini ferous tu bule volume increases Differentiation and development of the testis owing to an increment in tubul ar length, not diameter. Sertoli cell s a re a lso f unc ti o na ll y acti ve during The foetal period chil dhood: they produce high amounts of anti-Mulleri an horm o ne during the w ho le prepubert a l pe ri od, and In the human foetus, a thickening of the coelomic in hibin B until the age of 2-4 years. A nti-Mulleri an epithelium covering the anterior surface of th e meso­ hormone and inhibin seem to playa role as modulators nephros on each side of the body represents the anl agen of th e proliferati on and diffe rentiati on of Leydig cell of th e gonads. Although th e sex is determined by th e precursors. chromosomal complement (46,XY or 46,XX) resulting at th e time of fe rtilisati on, the male or female gonads Key words: Childhood, androgens, A nti-M ull erian cannot be distinguished at the microscopic level before hormone, Sertoli cell s, inhibin the end of the 7th week; by then, in the male foe tus, the expression of the S RY (Sex-determining Region of the Y chromosome) gene results in th e differenti ation of the Introduction gonad along the testi cul ar pathway (Berta et aI. , 1990; Sinclair et aI. , 1990). Other autosomal genes are also The testes are composed of two morphologically and implicated in gonadal diffe rentiatio n: WT-1 (Wilm 's functionall y di ffe rent compartments: th e seminife rous Tumour 1) (Kreidberg et ai. , 1993) and SF-1 (Steroido­ tubules, where the male gamete is produced, and th e genic Factor 1) (Luo et ai. , 1994) are essential fo r the intersti tia l tissue, respons ib le fo r the secre ti o n of development of the urogenital ridge, while mutations or androgens. The seminife rous tu bules contain two distinct deletions of SOX-9 (SRY HMO-box, gene 9) (Foster et cel\ populati ons: the Sertoli cells are somatic cells which a I. , 1994) or other putati ve genes located on the short arm of chromosome 9 (Bennett et ai. , 1993) and on the Offprint requests to: Dr . Rodollo Rey , Centro de Investigaciones long arms of chromosomes 7 (Seller et aI. , 1997) and 10 Endocrinol6gicas, Hospital de Ninos, Gallo 1330, (1425) Buenos Aires, (Wilkie e t a I. , 1993) result in abno rm al testi cul ar Argentina. Fax: +54- 11·4963-5930. e- mai l: [email protected] .ar diffe rentiation. 992 Prepubertal testis: a quiescent organ? The first morphologically identifiable event in Pelliniemi et aI., 1996). Testos terone secretion is testicular differentiation is the development of the Sertoli essential for the virilisation of the Wolffian ducts, which cells, which aggregate to form the seminiferous cords differentiate to form the internal male gonaduct, and of that will be colonised by the primordial germ cells the external genitalia. travelling from the stalk of the allantois. By the end of the 7th week, Sertoli cells begin to synthesise anti­ The postnatal period Mullerian hormone (AMH) (Fig. 1), the first Sertoli-cell specific protein expressed by the foetal gonad (Tran et The aspect of the adult testis is significantly different aI., 1977; Josso et aI., 1993). AMH, also known as from that of the gonad in the new-born (Fig. 3). The Mullerian inhibiting substance (MIS) (Lee and Donahoe, most notorious changes take place in the seminiferous 1993), is responsible for the regression of the Mullerian tubule compartment, where Sertoli cells show morpho­ ducts, which differentiate to form the uterus and logical maturation (Fig. 4) and spermatogenesis reaches Fallopian tubes in the female (Fig. 2). Soon afterwards, complete development. Spermatogenesis is a complex Sertoli cells begin to express other specific markers, like process, involving mitotic and meiotic divisions and SGP-2 or c1usterin (Taketo, 1991). The immature aspect diffe rentiation of germ cells, through which th e of Sertoli cells does not change during the remaining undifferentiated diploid germ cells give rise to haploid foetal life. spermatozoa. As a result of the proliferation of germ Primordial germ cells, or gonocytes, express a cells and of the maturation of Sertoli cells, the membrane-bound receptor known as c-kit, of vital seminiferous tubules acquire a lumen and dramatically importance for germ cell migration to the gonad (Orth et increase their diameter. In the interstitial tissue, Leydig aI., 1997) and for their adhesion to Sertoli cells (Pesce et cells differentiate from mesenchymal precursors. The aI., 1997), which express the c-kit ligand (Rossi et aI., mature male gonad has an intense secreting capacity and 1991; Tajima et aI., 1991), known as Steel Factor. Once produces high quantities of androgens, inhibin, activin, harboured in the sex cords, where they occupy a central and androgen-binding protein, which have been used as position surrounded by Sertoli cells, the gonocytes markers of adult testicular function. proliferate vigorously until late foetal life (Huckins and Most of the aforementioned changes take place Clermont, 1968), but they do not enter meiosis. during puberty: in a period of 4 to 6 years, the testicular In the interstitial tissue, Leydig cells differentiate during the 8th week of foetal life. The presence of an LH/hCG receptor capable of binding placental hCG on Leydig cell membrane is essential for further develop­ ment and multiplication of foetal Leydig cells (Kremer et aI., 1995; Laue et aI., 1995), which reach peak numbers between weeks 16 and 24; thereafter, Leydig cell number progressively decreases until birth (Codesal et aI., 1990). As soon as they differentiate, Leydig cells begin to express steroidogenic enzymes involved in testosterone biosynthesis, as well as other peptides that are secreted and might playa role in paracrine or endocrine regulatory mechanisms (for review, see . '- Fig. 2. Hormonal regulation of sex differentiation. Anti -Mullerian hormone, secreted by Sertoli cells and acting through a membrane­ bound receptor, inhibits the development of Mullerian ducts, which give ,.- .. ,. .. rise to the Fallopian tubes, uterus and upper part of the vagina in the .. ~ . " .. _ . ~"" . t. ...'4; :6\ i: female foetus. Testosterone, produced by Leydig cells and acting j"";""" ~_ ' '; ~/1''r. .' ~ :,..v . :~... ",- _ ,'.~ through the intracellular androgen receptor, induces the development of 'r ' ",. Wolffian ducts to form the epididymis, vas deferens and seminal vesicle. I . - ~ ---- Transformation of testosterone to dihydrotestosterone (DHT), which also Fig. 1. Localisation of anti-Mullerian hormone (AMH) expression by in binds to the same androgen receptor, is essential for the virilisation of situ hybridisation using a digoxigenin-Iabelled riboprobe in an 8 week­ the urogenital sinus and external genitalia (Reproduced with permission old male foetus gonad. The slide was slightly counterstained with from: Rey R and Picard JY, Embryology and endocrinology of genital hematoxylin, Sertoli cells in the seminiferous cords express AMH development. Bailliere's Clinical Endocrinology and Metabolism 1998; intensely. x 50 12:17-33) . 993 Prepubertal testis: a quiescent organ? volume grows from 1-2 cm3 to 20-25 cm3, the However, the use of morphometric techniques to study seminiferous tubule diameter increases from -50,um to small quantitative changes in testicular histology and the -250 ,urn, and serum testosterone levels that are almost analysis of non-traditional testicular markers have shown undetectable in the prepubertal boy reach adult levels.