52 GREATER PHENOTYPIC VARIABILITY IN CLONED CATTLE FETUSES FROM ONE CELL LINE THAN CONTEMPORARY HALF-SIBS GENERATED BY ARTIFICIAL INSEMINATION OR IN VITRO EMBRYO PRODUCTION

Abstract

The cloning of cattle by somatic cell nuclear transfer (NT) is associated with considerable variation in developmental abnormalities. Some of this variation may be due to the cell types/lines used and the specific production and culture methods for NT embryos. Fetal and placental development were studied in 24 pregnancies generated by NT (Wells et al., 2003 Theriogenology 59, 45–59) from a granulosa cell line. The controls consisted of 11 and 14 pregnancies resulting from in vitro-produced embryos (IVP) and artificial insemination (AI), respectively. All fetuses shared the same Friesian sire; oocytes for the derivation of NT or IVP embryos were obtained from abattoir-derived ovaries of Friesian cows. Morphometric measurements were made on the fetuses, fetal membranes, fluid volumes and placentomes at Days 50, 100 and 150 of gestation after slaughter. Pairwise comparisons of within group variances between the treatment groups were made using the F-test. The pregnancy loss from AI or embryo transfer to Day 150 was ∼40% for the AI and IVP groups. However, 60% of NT embryos transferred had been lost by Day 150. NT fetal weights at Day 100 were more variable than for the AI (P < 0.001) and IVP (P < 0.05) groups. The NT crown-rump lengths were also more variable compared with the IVP (P < 0.05) but not the AI group. At Day 100, NT heart (P < 0.01), kidney (P < 0.01) and liver (P < 0.05) weights were more variable compared with the AI group; both liver (P < 0.05) and kidney (P < 0.01) weights were similarly more variable in the Day 150 NT group. Part of this variability may be due to disproportionate organ growth in NT fetuses. Increased variability was most evident in the utero-placental tissues. At Day 50, the total fetal membrane weights were more variable in the NT compared with the AI (P < 0.001) but not the IVP group. The Day 50 IVP membrane weights were also more variable (P < 0.05) than for the AI group. The greater variability of the Day 150 NT membrane weights, when compared with AI (P < 0.05) or IVP (P < 0.01), could be due partly to greater variation in the allantoic and amniotic fluid volumes. Placentome numbers were significantly lower in the surviving Day 100 NT pregnancies but the weights of the total maternal caruncular tissue of the placentomes were significantly higher and more variable in the NT group (P < 0.05 for both AI and IVP). Placentome numbers in surviving NT pregnancies at Day 150 were similar to the controls. However, the total caruncle weights in both the NT and IVP groups were more variable when compared with the AI group (P < 0.05 for both). Thus, there is greater variability in fetal membrane and placental development in NT and, to a certain extent, IVP fetuses, when compared with the AI group. The increased variability within this NT group suggests that epigenetic effects arising from incomplete reprogramming of the donor genome and embryo culture can override genetic traits to a certain extent. Supported by FRST C10X0018.