Maternal mRNAs

Evans, T., Rosenthal, E. T Youngblom, J., Distel, D., and Hunt, T. (1983). Cyclin a protein specified by maternal mRNA in sea urchin eggs that is destroyed at each cleavage division. Cell 33 389-396. 

Kubiak No, the majority of maternal mRNA is only degraded before the second mitosis. There are some mRNAs, however, that persist until the blastocyst stage. 

Degradation or maternal proteins Disappearance of maternal mRNAs... 

Eehner What I understood so far about timers in the early frog embryos is that most people think that they involve an mRN A based mechanism. Maternal mRNAs have a limited stability and disappear suddenly. 

Klymkowsky, M. W., Maynell, L. A., and Nislow, C. (1991). Cytokeratin phosphorylation, cytokeratin filament severing and the solubilization of the maternal mRNA Vgl. J. Cell Biol. 114, 787-797. 

We turn now to determination of the anterior/posterior axis in the early fly embryo while it is still a syncytium. As in determination of the dorsal/ventral axis, specification of anterior/posterior cell fate begins during oogenesis. The initial asymmetry also involves so-called maternal mRNAs, which are produced by nurse cells and transported into the oocyte. In this case they become localized in discrete spatial domains (see Figure 15-14). For example, bicoid mRNA is trapped at the most anterior region, or anterior pole, of the early fly embryo (Figure 15-19). The anterior localization of... 

Gradients of transcription factors, produced from maternal mRNAs in the early Drosophila embryo, control the patterned expression of embryonic genes, leading to segmentation of the embryo along the anteroposterior axis. 

Svoboda P, et al. (2000). Selective reduction of dormant maternal mRNAs in mouse oocytes by RNA interference. Development. 127(19) 4147-4156. 

Maskin is a cytoplasmic polyadenylation element-binding protein-associated factor. Dormant state of maternal mRNAs in immature oocytes is maintained by an abortive interaction of this protein with the eukaryotic initiation factors 4E and 4G. Phosphorylation of maskin promotes the dissociation of this interaction, thereby allows the dormant mRNAs to be translated actively. Aurora phosphorylation of maskin is reported to be involved in protein synthesis in maturing clam and Xenopus oocytes and in centrosome-dep>endent microtubule assembly at mitosis (Kinoshita et al. 2005 Pascreau et al. 2005). 

Monesi et al. (1970) suggested that both newly synthesized mRNA and mRNA of maternal origin are utilized during cleavage although it has also been suggested that maternal mRNA s may be utilized exclusively (Chapman et al., 1971). The assay of poly (A) sequences as markers for monitoring mRNA synthesis will very likely be a useful tool in the clarification of this problem in the future. 

In the mammalian egg, the synthesis of RNA starts shortly after fertilization. There is also a rapid increase in protein synthesis after fertilization, and the evidence reviewed suggests that this is probably the result of both the initiation of new mRNA synthesis as well as the activation of masked maternal mRNA in the cytoplasm or the assemblage of active ribosomes. The first morphological differentiation which may be observed is a distinction between the inner cell mass and the trophoblast cells which, in the normal mouse embryo, occurs at the late blastocyst stage at a time when the embryo contains between 30 and 60 cells. The outer trophoblast develops into the placenta and extraembryonic membranes, while the inner cell mass continues to differentiate to give rise to the fetus. 

After the mRNA has been transported into the cytoplasm it may be stored, or at least be unavailable for translation, for some time. The best example of this is found in amphibian and sea urchin oocytes, which accumulate substantial amounts of maternal mRNA s only trans-... 

More recent work from Gross laboratory claims that at least some maternal mRNA s code for microtubule proteins, or, more correctly, for soluble proteins which, after partial purification by vinblastine precipitation, co-migrate on acrylamide gel electrophoresis with known microtubule proteins from sperm tails (Raff et ah, 1971, 1972). Although there is a pool of these microtubule proteins in the unfertilized egg it seems that this pool is maintained or supplemented (for the construction of such things as mitotic spindles and cilia) by continuous synthesis of the monomeric subunits from stored mRNA, starting from the first cleavage cycle. Hopefully, more detailed analysis of the relative rate of microtubule synthesis at different times after fertilization, in the absence of new RNA synthesis, will provide information about the way in which this particular maternal mRNA is utilized during development. 

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