Reproduction in Domestic Animals

286 KC Caires, JA Schmidt, AP Oliver, J de Avila and DJ McLeanneonatal boar ages evaluated (Fig. 2e). This suggeststhat testosterone may directly or indirectly regulate thehomeostasis of these cell types in the neonatal boartestis, potentially contributing to the observed donor agevariation in the establishment of spermatogenesis in thegrafting study, and it is known that post-natal testisdevelopment is conserved between grafted and in vivotestis tissue (Oatley et al. 2004; Zeng et al. 2006).Our results demonstrate age-related differences in thepotential of neonatal testis tissue to grow and supportcomplete germ cell differentiation when grafted onimmunodeficient mice. More importantly, these findingsindicate important physiological changes in germ andSertoli cell homeostasis during neonatal testis developmentin the boar, and may explain why previousattempts to increase testis size and sperm productionin boars have been unsuccessful. This conclusion issupported by in vivo evidence (At-Taras et al. 2006,2008), and as a result we suggest future efforts to impactlifetime fertility in boars should occur during the first2 weeks of neonatal life.From an application standpoint, tissue originatingfrom 14-day boar testis resulted in the greatest degree ofgraft germ cell differentiation; this stage in developmentmay be ideally suited for germ line genetic manipulationof cells, potentially facilitating a novel means to producetransgenic boar spermatozoa. Further, as Sertoli cellsprovide an immunoprotective barrier for developinggerm cells, neonatal porcine Sertoli cells have seenincreasing use to encapsulate porcine islet cells prior totransplantation in human patients with diabetes mellitus(Dufour et al. 2003; Valdes-Gonzalez et al. 2007), andthus a better understanding of the basic mechanismsregulating their homeostasis, and survival after transplantationis necessitated. We also demonstrated nodifferences in the ability of cryopreserved and freshlygrafted donor porcine testis tissue to grow, producetestosterone and establish spermatogenesis. Thus, assomatic cell function is restored after freezing, cryopreservationof pre-pubertal testis tissue prior to graftingpresents a novel means for male germ linepreservation. The factors regulating the biologicalactivity of Sertoli and germ cell homeostasis in theneonatal boar testis will be the focus of future experimentsand may provide insights for both agriculturaland biomedical applications.AcknowledgementThis research was supported in part by a graduate research fellowshipprovided by the Seattle Chapter of the Achievement Rewards forCollege Scientists Foundation on behalf of K.C.C.ReferencesAlmeida FF, Leal MC, Franca LR, 2006: Testis morphometry,duration of spermatogenesis, and spermatogenic efficiencyin the wild boar (Sus scrofa). Biol Reprod 75, 792–799.Amann RP, 1970: Sperm production rates. 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