Evaluation of Gestational Deficiencies in Cloned Sheep Fetuses and Placentae1

Abstract

Sheep fetal development at 35 days of gestation was examined following natural mating, in vitro production (IVP) of fertilized embryos, or somatic cell nuclear transfer (NT). Five crossbred (Blackface x Black Welsh) and four purebred (Black Welsh) fetuses and their associated placentae produced by natural mating were morphologically normal and consistent with each other. From 10 ewes receiving 21 IVP embryos, 17 fetuses (81%) were recovered, and 15 of these (88%) were normal. The NT fetuses were derived from two Black Welsh fetal fibroblast cell lines (BLW1 and 6). Transfer of 21 BLW1 and 22 BLW6 NT embryos into 12 and 11 ewes, respectively, yielded 7 (33%) and 8 (36%) fetuses, respectively. Only three (43%) BLW1 and two (25%) BLW6 NT fetuses were normal, with the rest being developmentally retarded. The NT fetal and placental deficiencies included liver enlargement, dermal hemorrhaging, and lack of placental vascular development reflected by reduced or absent cotyledonary structures. Fibroblasts isolated from normal and abnormal cloned fetuses did not differ in their karyotype from sexually conceived fetuses or nuclear donor cell lines. Our results demonstrate that within the first quarter of gestation, cloned fetuses are characterized by a high incidence of developmental retardation and placental insufficiency. These deficiencies are not linked to gross defects in chromosome number.

Developmental arrest of scNT‐derived fetuses by disruption of the developing endometrial gland as a result of impaired trophoblast migration and invasiveness

“…Most placentas from sheep at day 30 after scNT embryo transfer display avascularization and hypovascularization (De Sousa et al, 2001) effects that are also observed in our studies with pigs. To confirm the data, the level of angiogenic-related molecules such as VEGF, ANG-1 and -2, VEG-FRI, VEGF-RII, and TIE-2 mRNA was determined in control and scNT placentas by real-time RT-PCR (Fig.…”

Massive dysregulation of genes involved in cell signaling and placental development in cloned cattle conceptus and maternal endometrium

“…Thus, multiple lines of experimental evidence have led to the conclusion that EET is the origin of the developmental pathologies in placentation of SCNTderived clones (17,(22)(23)(24)(25)(26). Therefore, study of the communication between cloned conceptuses and the endometrium should yield important insights into the mechanisms underlying average losses of ∼60% of cloned embryos before implantation and 80% of fetuses within the first trimester of gestation (27,28).…”

Placental function in development and disease

“…Initial studies had described only the placenta in those rare pregnancies that made it to term. In cattle and sheep, the term placenta in clones is characterised by a reduced number of cotyledons, hydroallantois and hypertrophy of remaining placentomes (Hill et al 1999;De Sousa et al 2001). Interestingly, the maternal caruncles are also underdeveloped, implying that primary fetoplacental defects indirectly affect the mother also (Hashizume et al 2002).…”