Reproduction in Domestic Animals

Reprod Dom Anim 43 (Suppl. 2), 280–287 (2008); doi: 10.1111/j.1439-0531.2008.01175.xISSN 0936-6768Endocrine Regulation of the Establishment of Spermatogenesis in PigsKC Caires, JA Schmidt, AP Oliver, J de Avila and DJ McLeanWashington State University, Pullman, Washington, USAContentsSomatic and germ cell maturation precedes the start ofspermatogenesis and is coordinated, so efficient spermatogenesiswill occur in the adults. The present study was conductedto evaluate endocrine regulation of germ and somatic cellhomeostasis in the neonatal boar testis associated with theestablishment of spermatogenesis. Testis tissue obtained from3-, 5-, 7- and 14-day-old piglets were ectopically xenograftedonto castrated, immunodeficient nude mice. Grafts wereremoved 22 weeks later and evaluated for growth and theestablishment of spermatogenesis. Recipient mouse testosteronebiosynthesis and follicle-stimulating hormone (FSH)concentrations were also assayed. Testis tissue graft growthwas significantly greater in testis grafts from 3-day donortissue when compared to all other ages; 5-, 7- and 14-day-olddonor tissue weights were not significantly different atremoval. Follicle-stimulating hormone concentrations inrecipient mice supporting testis grafts from 5-, 7- and14-day-old donor tissues did not differ and were similar tonormal physiological levels in age-matched, intact nude mice.Serum FSH levels were significantly lower in recipient micesupporting testis grafts from 3-day-old donor tissue. Radioimmunoassayand biological assay indicated no differences intestosterone production by testis tissue grafts of varyingdonor age. Porcine testis tissue obtained from 3-, 5-, 7- and14-day-old neonatal boars were all capable of producinground and elongate spermatids after 22 weeks of grafting, buttestis grafts from 14-day-old donors had a significantlygreater (eightfold) percentage of seminiferous tubules withspermatids compared to all other donor ages (p < 0.05).Cryopreservation did not affect the ability of testis tissuegrafts to grow, produce testosterone or establish spermatogenesiswhen compared to controls (p < 0.05). Collectively,these data demonstrate intrinsic differences in the biologicalactivity of germ and somatic cell populations during neonatalboar testis development associated with the establishment ofspermatogenesis.IntroductionSpermatogenesis is an organized process requiring manysystemic and local factors (Zirkin 1998; Parvinen andVentela 1999) and includes all cellular transformationsthat occur within the seminiferous epithelium leading tothe production of mature spermatozoa in the seminiferoustubule of the testis. Yet, germ cell interactionswith nearby Sertoli cells are necessary for germ cells toundergo mitosis, meiosis and spermiogenesis (Russellet al. 1990). Furthermore, it is believed that Sertoli cellscontribute to the process of spermatogonial stem cell(SSC) renewal (McLean 2005), allowing for continualproduction of sperm during a male’s adult life span.Leydig and Sertoli cells also account for the majority oftestosterone and oestrogen synthesis in the male (Waiteset al. 1985), and secrete factors exerting negative feedbackon the pituitary gland; both processes promotingnormal male fertility (Padmanabhan and Sharma 2001;Plant and Marshall 2001).The majority of information about the cell biologyassociated with spermatogenesis has been gained withthe use of rodent models and as a result, there remains ageneral lack of knowledge regarding testis developmentand sperm production in livestock. Further, due to thecomplexity involved with germ cell differentiation, mostresearch investigating testis biology is often restricted toin vitro studies. Although insightful, the intimate relationshipbetween Sertoli cells and germ cells are oftenlost, and cell lines can mutate during culture. Ectopictestis tissue xenografting is a procedure whereby smallpieces of testicular parenchyma from a donor animal aregrafted under the skin of an immunodeficient nudemouse. This technique maintains interactions betweengerm and somatic cells in the grafted tissue and thusprovides a biological assay for the establishment ofspermatogenesis in a variety of species (Honaramoozet al. 2002; Oatley et al. 2004). Additionally, multiplestudies have demonstrated that testis tissue xenograftsare representative of in vivo testis development (Schmidtet al. 2006; Zeng et al. 2006).The onset of puberty is commonly associated with thecompletion of the first wave of spermatogenesis in avariety of species (Amann 1970). It is known that Sertolicell number established before puberty determines adulttestis size (Russell 1993; Sharpe et al. 2000) and maturespermatogenic capacity (Orth et al. 1988) in variousmammalian species. Puberty in most domestic pigbreeds occurs around 20 weeks of age (Lunstra et al.1986) and researchers have investigated the establishmentof the spermatogenesis in the post-natal boar testisfrom 1 month of age to adulthood (Lunstra et al. 2003;McCoard et al. 2003; Almeida et al. 2006), but little isknown about relationships between somatic and germcells in the neonatal testis. Although porcine Sertoli cellsstill express markers of proliferating cells around4 months of age (Klobucar et al. 2003), several reportssuggest the importance of Sertoli cell proliferation in theboar testis during the first 2 weeks of life and neonatally(McCoard et al. 2001, 2003). This represents severalcandidate physiological stages in development that maygovern the spermatogenic capacity of the mature boartestis.Porcine Sertoli cell numbers increase fourfold duringthe first 2 weeks of neonatal life, and this represents animportant time for Sertoli cell homeostasis, thus wehypothesized that testicular tissue from 14-day-oldboars would have the greatest ability to establish andsupport spermatogenesis following grafting when comparedto other donor ages. We also predicted that nodifferences in testis graft androgen biosynthesis orÓ 2008 The Authors. Journal compilation Ó 2008 Blackwell Verlag