Additional file 2.

Gene expression levels of candidate genes to reveal timing of midblastula transition in cod. mRNA levels of 3 candidate genes were measured in oocyte, 1-2 cell, blastula and gastrula stage. mRNA levels are relative to hba. Bars with different letters represent significant different mRNA levels for each gene. All data are shown as mean with SEM. Nā€‰=ā€‰3. The maternal candidate chosen was the eukaryotic translation initiation factor 4E (eif4e) in which the 1b variant is found in oocyte and early embryo only in mouse (eif4Elooeif41b; [21]) and zebrafish [55]. Syntenic analysis in cod did not reveal eif41b, suggesting that this gene has been lost in this species (Data not shown, [27]). We measured eif41a, and mRNA levels significantly decreased from 1-2 cell stage to gastrula. In contrast, Robalino [57] detected a constant level of eif41a in oocyte and early embryo. eif41a is involved in recruiting cytoplasmic mRNA and initiation translation [58], and higher levels of eif41a generally correlate with increased protein synthesis and cell growth [59]. To indicate MZT, the TATA box binding protein (tbp) was selected. During early cleavage maternal stores of tbp are translated and by MBT the protein contribute to transcription initiation in Xenopus[60] and zebrafish [61]. tbp is also involved in degradation of maternal mRNAs [62], another main feature of MZT. In accordance with this, we detected a gradual decrease in tbp mRNA levels from oocyte until blastula. At gastrulation zygotic gene expression is presumably active, and one early zygotic gene in zebrafish is no tail (t), which is expressed in nuclei of the germ ring of the late blastula and early gastrula [63,64]. Likewise we did not detect expression of this gene until gastrula, where it was highly expressed.

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Kleppe et al. BMC Genomics 2012 13:443   doi:10.1186/1471-2164-13-443