Uncovering the roles of 5′UTRs in translational control during early zebrafish development

Following fertilisation, metazoan embryos are transcriptionally silent, and embryogenesis is controlled by maternally deposited factors. Developmental progression requires the synthesis of new mRNAs and proteins in a coordinated fashion.

Many posttranscriptional mechanisms regulate the fate of maternal mRNAs, but it is less understood how translational control shapes early embryogenesis. In eukaryotes, translation starts at the mRNA 5′ end, consisting of the 5′ cap and 5′ untranslated region (UTR). Protein synthesis is primarily regulated at the translation initiation step by elements within the 5′UTR.

However, the role of 5′UTRs in regulating the dynamics of mRNA translation during vertebrate embryogenesis remains unexplored.

For example, all vertebrate ribosomal protein (RP) mRNAs harbor a conserved terminal oligopyrimidine tract (TOP) in their 5′UTR.

RP levels must be tightly controlled to ensure proper organismal development, but if and how the TOP motif mediates RP mRNA translational regulation during embryogenesis is unclear. Overall, we lack a systematic understanding of the regulatory information contained in 5′UTRs.

In this work, I aim to uncover the 5′UTR in vivo rules for mRNA translational regulation during zebrafish embryogenesis.

I propose to apply imaging and biochemical approaches to characterise the role of the TOP motif in RP mRNA translational regulation during embryogenesis and identify the trans-acting factor(s) that bind(s) to it (Aim 1).

To systematically assess the contribution of 5′UTRs to mRNA translational regulation during zebrafish embryogenesis, I will couple a massively parallel reporter assay of 5′UTRs to polysome profiling (Aim 2).

By integrating the translational behaviour of 5′UTR reporters throughout embryogenesis with sequence-based regression models, I anticipate to uncover novel cis-regulatory elements in 5′UTRs with developmental roles.