The roles of alternate transcripts and uORFs in regulating meiotic translation 

(collaboration with the Ünal lab)


The layered setup of our survey of meiotic gene expression allowed us to observe the interplay between transcriptional and translational control, providing a rich view of the integration of gene regulation that underlies the complex cellular remodeling and chromosome segregation associated with meiosis. We identified an interesting example of such regulation for the conserved DNA replication factor, Orc1. Orc1, a member of the six factor Origin Recognition Complex, is required for both mitotic and meiotic DNA replication. In meiosis, a longer transcript of ORC1 is seen in the cell after meiotic DNA replication is completed. This longer transcript allows only poor translation of Orc1 protein while subject to efficient translation of several uORFs in the leader. These uORFs appear to compete with the ORC1 ORF for translation capacity, and reduce the amount of this essential factor at a time that meiotic cells no longer require it. 

Orc1 protein synthesis is controlled by uORF-mediated translation competition on a regulated long meiotic transcript isoform. mRNA and ribosome footprint sequencing are shown for ORC1 , with mitotic cells in the top (black) track and meiotic progression proceeding from top to bottom below that. In mitotic and early meiotic cells, a short transcript is present that allows Orc1 translation and doesn't contain uORFs. Following meiotic translation, a longer transcript is observed, with several AUG uORFs translated that appear to prevent ribosomes from translating the ORC1 ORF. 

Orc1 protein synthesis is controlled by uORF-mediated translation competition on a regulated long meiotic transcript isoform. mRNA and ribosome footprint sequencing are shown for ORC1 , with mitotic cells in the top (black) track and meiotic progression proceeding from top to bottom below that. In mitotic and early meiotic cells, a short transcript is present that allows Orc1 translation and doesn't contain uORFs. Following meiotic translation, a longer transcript is observed, with several AUG uORFs translated that appear to prevent ribosomes from translating the ORC1 ORF. 

We identified ~100 other examples of such regulation, often of important genes in driving the meiotic program. One particularly interesting example is the conserved kinetochore component, Ndc80, which is strongly translationally regulated in meiosis, though with very different kinetics than is seen for Orc1. Ndc80 translation is kept low early in meiosis through the presence of a longer transcript with competitive uORFs prior to the first round of meiotic chromosome segregation. When this regulation is disrupted, the meiotic pattern of chromosome segregation does not occur properly (Miller and Ünal et al., eLife, 2012).

In collaboration with the Ünal lab, we are interested in understanding how the presence of competitive uORFs on regulated long transcripts drives normal meiotic progression. We are investigating the basis for the transcriptional and translational control responsible, as well as the cellular significance of such regulation for Orc1, Ndc80, and other genes of interest.

 

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