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10.3.2.1 Examples of Selective Protein Degradation During OET
ELAVL2 Elimination During NSN/SN Transition in Fully Grown Mouse
Oocytes
Elavl2 encodes one of the ARE-binding proteins, which act in the ARE-mediated
mRNA decay or translation control (reviewed in Garneau et al. 2007 ; see also
Chap. 2 ). Mouse oocytes express a short ELAVL2 isoform that acts as a pleiotropic
translational repressor. Elavl2 mRNA is stable during meiotic maturation and is
downregulated after fertilization. In contrast, ELAVL2 protein rapidly decreases
already at the end of the oocyte growth phase, during the NSN/SN transition, which
makes it a rare example of a protein eliminated during Phase 0. Functional analyses
of ELAVL2 suggested that it is important for efficient production of fully grown
oocytes, while its removal during NSN/SN transition might contribute to the acqui-
sition of the developmental competence (Chalupnikova et al. 2014 ). The molecular
mechanism of ELAVL2 degradation remains unclear, but the selectivity of its
destabilization suggests that the ubiquitin-proteasome system is at play.
CPEB Degradation During Meiotic Maturation in Xenopus Oocytes
CPEB is a cytoplasmic polyadenylation element-binding protein, which plays an
important role in coordinated translational control of dormant maternal mRNAs in
Xenopus oocytes (Pique et al. 2008 ) and elsewhere (reviewed in Richter 2007 ; see
also Chap. 2 ). In maturing Xenopus oocytes, CPEB is phosphorylated and degraded
by the ubiquitin-proteasome system, and this degradation facilitates entry into the
second meiotic division (Reverte et al. 2001 ; Mendez et al. 2002 ). CPEB degrada-
tion during meiotic maturation was observed also in mammalian oocytes (Uzbekova
et al. 2008 ; Hodgman et al. 2001 ).
Selectivity of CPEB degradation is mediated by a specific F-box protein
β-TrCP in the SCFβ-TrCP E3 ubiquitin ligase complex, which recognizes a specific
CPEB sequence (Setoyama et al. 2007 ). SCFβ-TrCP binding depends on a specific
phosphorylation in the recognition motif. According to the model, CDC2 and
PLX sequentially phosphorylate CPEB during meiotic maturation and target it for
degradation via SCFβ-TrCP (Setoyama et al. 2007 ).
10.3.2.2 Proteome Dynamics During OET
For decades, proteome analysis during OET had to rely on two-dimensional
(2D) electrophoresis (e.g., Link et al. 2006 ; Tay et al. 2006 ), often combined
with metabolic labeling. Compared to microarray analyses and next-generation
sequencing, proteome studies offer somewhat lower-resolution, but nonetheless
highly interesting, insights into proteome changes during OET. Given the
amount of material required for extensive proteome analysis, the most
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