-210 Nottingham - Nottingham eTheses - The University of Nottingham

deacetylases (HDACs). Trichostatin A (TSA) is a type of HDAC inhibitors. A
significant improvement in development has been reported in mice (Rybouchkin et
al., 2006), cattle (Zhang et al., 2007), and pigs (Zhao et al., 2009).
1.4.2.2.2 Treatment of donor cells with cell extracts
Epigenetic modification can be induced prior to SCNT by treatment of donor cells
with cell extracts. Rathbone et al. (2010) reported a method using permeabilised
ovine fetal fibroblasts pretreated with a cytoplasmic extract produced from germinal
vesicle (GV) stage Xenopus laevis oocytes. This was the first to report the birth of
live offspring and an increase in cloning efficiency following pretreatment with
transspecies extracts.
1.5 Problems specific to porcine cloning: asynchrony
between oocytes
Porcine oocyte maturation in vitro period is prolonged as compared to other farm
animal species and is characterised by a high level of asynchrony between oocytes.
On reaching MII, development is arrested and oocytes begin ageing. During meiotic
arrest nuclear status does not change, however, cytoplasmic changes occur when the
culture period is prolonged (Kikuchi et al., 1995). Spontaneous oocyte activation was
observed in porcine oocytes aged in vivo (Yanagimachi and Chang, 1961). Hunter
(1967) suggested that porcine oocytes aged in vivo resulted in abnormal fertilisation
and failure in the subsequent development of the embryos. Abnormalities of
development were also recorded in oocytes aged in vitro (Sato et al.,
1979). In
addition, ageing oocytes are characterised by a reduction in MPF activity (Kikuchi et
al., 1995). Therefore, although oocytes may be arrested at MII, the biochemical status
and developmental competence of each may differ and this may affect development
following SCNT.
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