Evidence for Placental Abnormality as the Major Cause of Mortality in First-Trimester Somatic Cell Cloned Bovine Fetuses1

Abstract

The production of cloned animals is, at present, an inefficient process. This study focused on the fetal losses that occur between Days 30-90 of gestation. Fetal and placental characteristics were studied from Days 30-90 of gestation using transrectal ultrasonography, maternal pregnancy specific protein b (PSPb) levels, and postslaughter collection of fetal tissue. Pregnancy rates at Day 30 were similar for recipient cows carrying nuclear transfer (NT) and control embryos (45% [54/120] vs. 58% [11/19]), although multiple NT embryos were often transferred into recipients. From Days 30-90, 82% of NT fetuses died, whereas all control pregnancies remained viable. Crown-rump (CR) length was less in those fetuses that were destined to die before Day 90, but no significant difference was found between the CR lengths of NT and control fetuses that survived to Day 90. Maternal PSPb levels at Days 30 and 50 of gestation were not predictive of fetal survival to Day 90. The placentas of six cloned and four control (in vivo or in vitro fertilized) bovine pregnancies were compared between Days 35 and 60 of gestation. Two cloned placentas showed rudimentary development, as indicated by flat, cuboidal trophoblastic epithelium and reduced vascularization, whereas two others possessed a reduced number of barely discernable cotyledonary areas. The remaining two cloned placentas were similar to the controls, although one contained hemorrhagic cotyledons. Poor viability of cloned fetuses during Days 35-60 was associated with either rudimentary or marginal chorioallantoic development. Our findings suggest that future research should focus on factors that promote placental and vascular growth and on fetomaternal interactions that promote placental attachment and villous formation.

First cloned swamp buffalo produced from adult ear fibroblast cell

“…Serum starvation may often result in reduced cell survival and increased DNA fragmentation, which in turn cause subsequent high embryonic loss after nuclear transfer (Shi et al, 2007). In bovine nuclear transfer, Hill et al (2000) recorded 50% to 60% loss of cloned pregnancies by day 100; these rates are comparable to the loss rates encountered in the current study.…”

“…Buffaloes that were pregnant on day 30 but not on day 45 or day 90 were considered to have undergone embryonic mortality or foetal mortality (FM), respectively (Vecchio et al, 2007). In nuclear transfer, first trimester losses of more than 50% are common for nuclear transfer pregnancy in cattle, sheep and goats (Hill et al, 2000). This study recorded FM of ∼50%, whereas the proportion of late gestation losses between day 90 and calving reached 91.7%.…”

“…In animals derived from cloning or in vitro culture procedures, a high incidence of placental abnormalities is found during both early and late gestation (Hill et al, 2000). Buffaloes that were pregnant on day 30 but not on day 45 or day 90 were considered to have undergone embryonic mortality or foetal mortality (FM), respectively (Vecchio et al, 2007).…”

“…Our results demonstrate that the frozen buffalo ear skin fibroblast cells could support the development of matured oocytes into the embryos, and the subsequent establishment of pregnancy to full term. It has been reported that factors such as age, type and treatment of donor cells, as well as embryo culture methods influence survival rates in the first trimester, and neonatal viability at term (Hill et al, 2000).…”

Bovine conceptus of Bos indicus produced by somatic cell nuclear transfer and parthenogenesis present morphological variations since the blastocyst stage

“…Changes in these embryos are morphological and chromosomal, leading to abnormal gene expression (Gjorret et al, 2005;Zhou et al, 2008). It is believed that these abnormalities and placental dysfunction are the main causes of embryonic loss in the embryonic period (Hill et al, 2000;Talbot et al, 2000;Maddox-Hyttel et al, 2003;Tveden-Nyborg et al, 2005;Alexopoulos et al, 2008).…”