Aberrant expression of developmentally important signaling molecules in cloned porcine extraembryonic tissues

Early embryonic losses are common in cloned embryos in the current cloning system. However, the reasons for embryonic losses in early developmental stages of cloned embryos remain unclear. To elucidate the cause of early defective development in cloned embryos, two porcine clones including extraembryonic tissues were obtained at 26 days of gestation. The expression of various molecules in developmentally important signaling pathways, including Notch, hedgehog (Hh), receptor tyrosine kinase (RTK), Janus kinase/signal transducer and activator of transcription (JAK/STAT), wingless related (Wnt), and transforming growth factor-β (TGF-β), was then examined in the extraembryonic tissues. Western blot analysis showed that the expression of key molecules involved in the Notch, Hh, RTK, and JAK/STAT signaling pathways was down-regulated, whereas most Wnt and TGF-β signaling pathway molecules were upregulated in cloned extraembryonic tissues compared to normal extraembryonic tissues. These results indicate that unbalanced coordination of signaling pathways might impair the early development of cloned embryos postimplantation, thereby resulting in embryonic losses during the first trimester.