For example, Hsp83 RNA is a component of the posterior polar plasm [ 57], and Hsp90 protein is required for localization of maternal mRNA to the posterior pole, which is essential for development of germ cells in the Drosophila embryo [ 58].
The recruitment of maternal mRNA for translation has long been recognized as a widespread mechanism to generate newly synthesized proteins in maturing oocytes and fertilized eggs [ 3].
In addition, the hermaphrodite germ line generates high levels of maternal mRNA for inclusion in oocytes, which will increase the germline contribution to the steady state transcript level in the gonad.
In zebrafish embryos, miR-430 facilitates the clearance of hundreds of maternal mRNA at the onset of zygotic transcription [38], and reporters encoding 3' UTRs from several of these mRNAs were shown to be deadenylated in a miR-430-dependent manner [38], [39].
This interesting and novel finding suggests a role of SUMO in regulating the functions of maternal mRNA by modifying components of oskar mRNP, and therefore could explain some of the pleiotropic defects observed in the embryonic patterning of embryos resulting from sumo mutant GLCs.
The precise mechanism(s) by which EGA is controlled is not well-understood, but studies in different model systems have implicated degradation of maternal mRNAs, repression of basic transcription factors, and induction of gene expression through a sequence-specific transcription factor (Guven-Ozkan et al. 2008; Liang et al. 2008; Tadros et al. 2007).
MZT is a two-step process of removal of a subset of maternal mRNA and proteins followed by the initiation of zygotic mRNA transcription (Tadros and Lipshitz 2009).
These results taken together with the results obtained using synthetic smad2 mRNAs suggest that the sustained levels of maternal mRNAs in TBP morphants are due to the inhibition of maternal mRNA degradation rather than ectopic activation of zygotic transcription of the respective genes.
To test if the inhibition of the degradation of maternal mRNA occurs in TBP morphants, we searched for maternally expressed genes in the TBP morphant microarray gene sets.
To verify the specificity of the maternal mRNA degradation phenotype to loss of TBP protein function, the ability of a MO-insensitive TBP mRNA to rescue the phenotype in TBP MO-injected embryos was tested.
