Research Summary

The research of the Laboratory of Biochemistry and Molecular Biology of Germ Cells is focused on the study of the mechanisms regulating the progression of mammalian oocytes through meiotic division, and on the molecular basis of the main morphological changes occurring during this process (nuclear envelope breakdown, formation of the spindle, chromosome condensation and segregation). Gametogenesis and fertilization are the key events in sexual reproduction. In the female, meiosis results in a large oocyte that is competent for fertilization and fundamental for the success of early embryonic development. One of the major problems occurring during mammalian meiosis is the high incidence of errors, leading to chromosomal aberrations, which are more prevalent in female gametes and seem to increase with maternal age. Oocyte aneuploidy has severe consequences including pregnancy loss or birth defects. Aneuploidy is believed to be a two-step process; initially an error occurs in the early meiotic program during recombination, which is then followed by a failure of the mechanisms controlling the chromosome segregation during the resumption of meiosis. To address the above issues, we currently concentrate on two major areas of research, which are studied in our laboratory:

Intracellular Venues of mRNA translation

A characteristic of early development in mammals is the reliance on the translation and utilization of stored RNAs and proteins rather than de novo transcription of genes in order to sustain rapid development. After a period of active transcription during growth, the nucleus of mammalian oocytes becomes transcriptionally inactive. Post-transcriptional control of gene expression at the level of translation has emerged as an important cellular function in normal development. In the absence of transcription, the completion of meiosis and early embryo development in mammals relies significantly on maternally synthesized RNAs. Therefore, the regulation of gene expression in oocytes is controlled almost exclusively at the level of mRNA stabilization and translation.

We discovered that the RNA distribution in this large cell type indicates a novel set of regulatory mechanisms needed to ensure specific gene expression at the right time and place. Spatial translational control may provide an important means to maintain and refine patterns of expression during the dynamic onset of meiosis.  Indeed, the distribution of certain transcripts and proteins appears to be distinct. This contributes to spindle and chromosome organization and thus plays an important role in the maintenance of genomic stability. Major causes of human aneuploidy involve errors that arise during meiosis. Our research suggest that mislocalization of specific transcripts within the oocyte and their aberrant translation could be another cause of aneuploidy. Our studies also suggest a spatio-temporally regulated translational control of chromosome segregation and formation of the functional spindle mediated by a mTOR/4F pathway during the meiotic progression of mammalian oocytes. Our projects investigate the translational components that are potential clinically relevant targets for the development of a healthy oocyte that sustains embryo development.

Translational activity (red) in the oocyte                                       Translation at the newly forming spindle

Our current work is focused on understanding the mechanisms of mRNA localization and translational bursts at the onset of meiosis with relation to genomic stability in the female germ cell, the oocyte.

Regulation of the activities of the most important M-phase protein kinases during oocyte meiotic maturation

Progression through both mitotic and meiotic cycles is controlled by the sequential activation and inactivation of a set of different protein kinases and phosphatases, which have been shown to play a critical role in the regulation of a large number of important events occurring in the cells during division. In our laboratory we aim to reveal the changes in timing and the degree of activation of important M-phase protein kinases which are essential for meiotic cell division in the mammalian female germ cells (oocytes).
Currently our lab is predominantly focused on the study of protein kinases, which are involved in the regulation of translation during oocyte meiotic maturation. This includes the study of kinases essential for the phosphorylation (and activation) of the CPEB1 protein which is needed for the activation of the cytoplasmic polyadenylation of specific mRNAs, resulting in their active translation. Recently, we have shown that Aurora A kinase activity is not important for this process in mammalian oocytes, although such a role has been suggested for Aurora A in other organisms. This suggests that some other kinases have to be involved in this process, and the nature of these kinases is the subject of our studies. Another kinase studied in the laboratory is mTOR (FRAP) kinase, which is crucially important for the cap-dependent initiation of the translation of specific mRNAs in the oocyte, and the regulation of its activity itself is a complex process involving several other kinases, which are also being investigated in our laboratory.

Adress:
IAPG AV ČR, v.v.i.
Laboratory of Biochemistry and Molecular Biology of Germ Cells
Rumburská 89
277 21 Liběchov
Czech republic