57 DEFECTIVE PLACENTAL VASCULARIZATION AND TROPHISMS IN FULL TERM SOMATIC CELL SHEEP CLONES

Abstract

We report on cloning experiments designed to explore the causes of peri- and post-natal mortality of cloned lambs. A total of 93 blastocysts obtained by nuclear transfer of somatic cells (granulosa cells) were transferred into 41 recipient ewes, and pregnancies were monitored by ultrasound scanning. In vitro-derived, fertilized embryos (IVF; n = 123) were also transferred in order to assess oocyte competence; naturally mated ewes (n = 120) were analyzed as well. Cloned embryos developed to the blastocyst stage and implanted at the same rate as IVF embryos. After Day 30 of gestation, however, dramatic losses occurred, and only 12 out of 93 (13%) clones reached full-term development, compared to 51 out of 123 (41.6%) lambs born from the IVF control embryos. Three full-term lamb clones were delivered stillborn as a result of placental degeneration. A further five clone recipients developed hydroallantois. Their lambs died within 24 h following delivery by Caesarean section; their carcasses displayed degenerative lesions in liver and kidney resulting from the severe hydroallantois. One set of twins was delivered by assisted parturition at Day 150, but died 24 h later due to respiratory distress syndrome. The remaining two clone recipients underwent Caesarean section; the corresponding two lambs displayed signs of respiratory dysfunction and died at approximately one month of age due to a bacterial complication. Blood samples collected from the cloned lambs after birth revealed a wide range of abnormalities indicative of kidney and liver dysfunction. Macroscopical and histopathological examination of the placentae revealed a marked reduction in vascularization, particularly at the apex of the villous processes, as well as a loss of differentiation of the trophoblastic epithelium. Our results strongly suggest that post-mortality in cloned lambs is mainly caused by placental abnormalities.