Reproduction in Domestic Animals

Reprod Dom Anim 43 (Suppl. 2), 245–251 (2008); doi: 10.1111/j.1439-0531.2008.01169.xISSN 0936-6768Fertilization and Early Embryonic Development in the Porcine Fallopian TubeK-P Bru¨ssow 1 ,JRátky 2 and H Rodriguez-Martinez 31 Department of Reproductive Biology, FBN Research Institute for the Biology of Farm Animals, Dummerstorf, Germany; 2 Department of Biology ofReproduction, Research Institute for Animal Breeding and Nutrition, Herceghalom, Hungary; 3 Division of Reproduction, Faculty of VeterinaryMedicine and Animal Science, Swedish University of Agricultural Sciences (SLU), Uppsala, SwedenContentsFertilization and early embryo development relies on acomplex interplay between the Fallopian tube and thegametes before and after fertilization. Thereby the oviduct,as a dynamic reproductive organ, enables reception, transportand maturation of male and female gametes, theirfusion, and supports early embryo development. This paperreviews current knowledge regarding physiological processesbehind the transport of boar spermatozoa, their storage inand release from the functional sperm reservoir (SR), and ofthe interactions that newly ovulated oocytes play within thetube during their transport to the site of fertilization.Experimental evidence of an ovarian control on spermrelease from the SR is highlighted. Furthermore, the impactof oviductal secretion on sperm capacitation, oocyte maturation,fertilization and early embryo development isstressed.IntroductionThe oviduct (synonyms Fallopian tube, salpinx, uterinetube) firstly described by Gabriel Fallopius in 1561, wasconsidered a simple connection between the ovary andthe uterus for a long time. Today, the oviduct isregarded as one of the most dynamic reproductiveorgans, whose functional aspects are not yet fullyunderstood (Rodriguez-Martinez et al. 2001). The oviductprovides a favourable environment for spermatozoa,enabling their transport and ensuring beneficialconditions during storage while preparing them forfertilization; as well as oocytes, making ovum pick-upand transport to the site of fertilization possible, whileensuring their final maturation. Both fertilization andearly embryonic development take place within theoviduct. This paper reviews physiological processesbehind the transport of boar spermatozoa, their storagein and release from the functional sperm reservoir (SR),and of the interactions that newly ovulated oocytes playduring their transport to the site of fertilization. Someaspects are highlighted, such as experimental evidencefor an ovarian influence on sperm release from the SRand the relevance of oviductal secretion on spermcapacitation, oocyte maturation, fertilization and earlyembryo development.The OviductThe porcine oviduct is approximately 25 cm in length(Bru¨ ssow 1985) and it is anatomically divided into threemain segments, e.g. the infundibulum, the ampulla andthe isthmus. Connecting areas, i.e. the terminal section(ostium), the ampulla-isthmic-junction (AIJ) and theutero-tubal-junction (UTJ) are also distinguished. Thehistoarchitecture of the Fallopian tube is simple, witha non-glandular mucosa (endosalpinx), covered with alining epithelium with secretory and ciliated cells,a double-layered smooth muscle (myosalpinx) and acovering serosa (mesosalpinx). Towards the ostium, thethickness of the internal, circular muscle becomesthinner; the longitudinal mucosal plicae gain complexityand the number of ciliated cells considerablyincreases (Rodriguez-Martinez et al. 2001; Yaniz et al.2006). This histoarchitecture builds tubal compartmentswith apparently different roles, all with optimal environmentwith regards to pH, osmotic pressure, nutrients,specific secretory products and signal molecules(reviewed by Rodriguez-Martinez 2007). Thus, preparationof gametes, fertilization and early embryonicdevelopment are supported and regulated by theoviduct.Sperm Transport and the Tubal SpermReservoirAfter deposition of spermatozoa in the cervix by matingor AI, a sperm subpopulation is rapidly transportedthrough the uterus, whereas the majority is eliminatedfrom the uterine lumen (Rodriguez-Martinez et al.2005). Spermatozoa that ascended the uterus in the firstphase of sperm transport colonize the UTJ and thecaudal isthmus (>10 4 spermatozoa), a segment thatacts as a functional pre-ovulatory sperm reservoir,temporarily arresting spermatozoa (up to 30 h) and,presumably, activating them at a given time (Rodriguez-Martinez et al. 2005). In the SR, most spermatozoamaintain normal ultrastructure and viability (Rodriguez-Martinezet al. 1990; Mburu et al. 1997). Severalconcerted factors are thought to explain the formationof the functional SR, including the narrowed lumen(Hunter 1984), viscous mucus (Johansson et al. 2000),lower temperature (Hunter and Nichol 1986), localenzymatic and ionic milieu (Rodriguez-Martinez et al.1991), selective binding of spermatozoa to the epithelium(Fazeli et al. 1999), and specific tubal fluid components(Tienthai et al. 2004), all which primarily leadto sperm quiescence.The sequential release of a restricted number ofspermatozoa from the SR towards the AIJ ensuresfertilization of oocytes within a time window, even ifovulation lasts over a longer interval. The periovulatoryprogression of spermatozoa is suggested to be a complexand concerted process including opening of the lumenby a decrease in the hormonally-driven endosalpingealoedema, dissolution of the hyaluronan (HA)-richÓ 2008 The Authors. Journal compilation Ó 2008 Blackwell Verlag