Nuclear export of single native mRNA molecules observed by light sheet fluorescence microscopy

Area of Science:

• Molecular Biology
• Cell Biology
• Biophysics

Background:

• Nuclear export of messenger RNA (mRNA) is a fundamental process in eukaryotic gene expression.
• Understanding the dynamics of mRNA transport through nuclear pore complexes (NPCs) is crucial for cellular function.

Purpose of the Study:

• To visualize and analyze the real-time dynamics of single native mRNA particles during nuclear export.
• To investigate the role of specific proteins, like hnRNP A1 and the RNA helicase Dbp5, in the mRNA export pathway.

Main Methods:

• Utilized light sheet microscopy to track fluorescently labeled mRNA-protein complexes (mRNPs) and nuclear envelope components in living Chironomus tentans salivary gland cells.
• Employed fluorescent tagging of hrp36 (hnRNP A1 homolog) and NTF2 for simultaneous visualization of mRNPs and NPCs.
• Analyzed the behavior of single fluorescent Dbp5 molecules at the NPC during export.

Main Results:

• Observed that mRNA particles frequently probe NPCs before successful export, with only 25% of probes resulting in translocation.
• Determined the complete export process duration ranges from 65 milliseconds to several seconds.
• Identified a rate-limiting step potentially involving the NPC's nuclear basket, suggesting mRNP repositioning and unfolding.
• Found that Dbp5 primarily interacts with the cytoplasmic face of the NPC, with an average binding duration of approximately 55 ms.

Conclusions:

• The study refines current models of mRNA export by providing high-resolution, dynamic insights into the process.
• Highlights the complex, multi-step nature of mRNA translocation through NPCs.
• Underscores the critical role of Dbp5 and potential NPC structures in regulating mRNA export efficiency.