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Kroll et al., 2002; Zhao et al., 2001 ). A comparison of the two elements
found that they were similar in size and relative position in the 3 0 -UTR
and contained critical subelements at either end of the sequence
( Bubunenko et al., 2002 ). Also, both LEs are characterized by dense and
overlapping clusters of Igf2bp3- and Ptbp1-binding motifs, suggesting that
this arrangement might be a general signal for the late localization pathway
( Bubunenko et al., 2002; Kwon et al., 2002 ). The overall similarity of vegt
and gdf1 elements suggests that RNP assembly and remodeling steps may also
be generally similar.
Despite these similarities with regard to RNA localization, Vegt protein
is not translated during oogenesis as is Gdf1 but instead is produced follow-
ing oocyte maturation ( Stennard et al., 1999 ). A defined translational control
element for Vegt translation in eggs has not been defined, and it is unclear
whether any of the proteins involved in gdf1 regulation also regulate vegt .In
this case, Vegt translation may not be linked to the completion of localiza-
tion, although it may be linked to delocalization during ovulation.
A maternal RNA-binding protein Rbm38 (Seb4r) has been identified as
a positive regulator of Vegt translation in the prospective endoderm, but
it is not known whether the protein is required during the oocyte-egg tran-
sition ( Souopgui et al., 2008 ).
3.2.3 Localization mechanisms of other late pathway RNAs
RNAs that clearly follow the late pathway include low-density lipoprotein
receptor adaptor protein 1 ( ldlrap1/xarh-alpha ; Zhou et al., 2003 ), zinc finger pro-
tein 36-like 2 ( zfp36l2/tis11d/c3h-3 ; Betley et al., 2002 ), bicaudal C homolog 1
( bicc1/bic-c ; Wessely and De Robertis, 2000 ), which encodes a KH-domain
RNA-binding protein, and velo1 ( Claussen and Pieler, 2004 ), which
encodes a protein similar to zebrafish Buc ( Bontems et al., 2009 ). Ldlrap1
and zfp36l2 contain clusters of CAC-containing motifs ( Betley et al.,
2002; Zhou et al., 2003 ), whereas bicc1 has a set of adjacent UUUCU
and UUCAC motifs ( Bubunenko et al., 2002 ). Although the localization
mechanisms of these RNAs have not been studied in any detail, based on
these characteristics and their expression patterns, localization mechanisms
are likely to be similar to gdf1 and vegt .
velo1 is interesting because its minimal localization element is only 75-nt
long and it lacks overlapping clusters of motifs found in gdf1 ( Claussen and
Pieler, 2004 ). RNA for velo1 bound a similar set of proteins as gdf1 in
UV-cross-linking experiments but showed a reduced affinity for Igf2bp3
in coimmunoprecipitation experiments ( Claussen and Pieler, 2004 ). Taken
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