Regulation of Cell Polarity and RNA Localization in Vertebrate Oocytes - International Review of Cell and Molecular Biology - page 161

A similar role has been described for Dnd1 regulation of its own mRNA in
Xenopus ( Koebernick et al., 2010 ), and it will be interesting to discover
whether Dazl has similar functions.
4.2.2 nos1
Consistent with its well-characterized germline functions in Drosophila ,
nanos1 is also required for PGC formation in both zebrafish and Xenopus .
Inhibition of Nos1 translation using MOs in either species leads to a mis-
migration of PGCs ( Koprunner et al., 2001; Lai et al., 2012 ), followed by
loss through apoptosis. Also similar to Drosophila , Xenopus Nos1 acts as a
translational inhibitor in conjunction with Pum2, and for transcriptional
silencing in PGCs, by directly or indirectly inhibiting C-terminal domain
phosphorylation of RNA pol II ( Lai et al., 2011 ). Interestingly, Nos1 is also
required to repress Vegt translation and destabilize its mRNA, in a PGC-
specific manner ( Lai et al., 2012 ). Thus, the germ plasm-containing cells
in the early blastula and gastrula require Nos1 for migration and survival
as well as to be protected from endoderm specification. It is important to
point out that although nos1 localizes to the mitochondrial cloud in oocytes
of both species, nos1 is not specific to the germ plasm in embryos in zebrafish
( Koprunner et al., 2001 ). Nos1 RNA is uniform initially but then degraded
in somatic precursors through miRNA-mediated degradation. By contrast,
Xenopus nos1 is restricted to the germ plasm and not somatically degraded
( Forristall et al., 1995 ). Nos1 protein is also translated specifically in the germ
plasm, through the use of a RNA-structure-based translational control ele-
ment near the 5 0 -end of the message ( Luo et al., 2011 ). It is not known to
what extent other germ plasm proteins are involved in regulating Nos1
translation in Xenopus .
4.2.3 germes and grip2
Two other germ-plasm-localized mRNAs with potential germline func-
tions are germes and grip2. Germes is a leucine zipper and EF-hand containing
protein that appears novel to Xenopus ( Berekelya et al., 2003, 2007 ). GFP
fusion proteins localize to the germ plasm, and two-hybrid studies suggested
an interaction with dynein light chains ( Berekelya et al., 2007 ). Dominant-
interfering constructs caused a reduction in PGCs and disruptions in germ
plasm morphology, suggesting that Germes may help control overall germ
plasm structure and localization, which would then contribute to defects in
PGC specification, migration, and survival ( Berekelya et al., 2007 ).