A stem-loop structure directs oskar mRNA to microtubule minus ends

Area of Science:

• Developmental Biology
• Molecular Cell Biology
• Genetics

Background:

• Intracellular mRNA transport and translational control are vital for protein localization in eukaryotes.
• In Drosophila, oskar mRNA localization to the oocyte posterior directs embryonic patterning.
• Previous studies identified the spliced oskar localization element (SOLE) for kinesin-1 mediated transport within the oocyte.

Purpose of the Study:

• To identify the signals responsible for the initial minus end-directed, dynein-dependent transport of oskar mRNA from nurse cells into the oocyte.
• To elucidate the RNA features mediating this early phase of mRNA transport during oogenesis.

Main Methods:

• Identification and functional analysis of a 67-nt stem-loop in the oskar 3' UTR.
• Assays for mRNA delivery to the developing oocyte and localization in blastoderm stage embryos.
• Ectopic expression studies in polarized follicular epithelium and salivary gland cells.

Main Results:

• A 67-nucleotide stem-loop in the oskar 3' UTR, termed the oocyte entry signal (OES), promotes oskar mRNA delivery into the oocyte.
• The OES mediates dynein-dependent transport and shares features with the fs(1)K10 oocyte localization signal.
• The OES drives apical localization of reporter RNAs in various cell types and embryonic stages, independent of cell type.

Conclusions:

• Two distinct cis-acting signals, OES and SOLE, mediate sequential dynein- and kinesin-dependent transport phases of oskar mRNA during oogenesis.
• The OES is a key determinant for the initial, minus end-directed transport of oskar mRNA into the oocyte.
• The OES promotes mRNA localization via dynein-dependent mechanisms, applicable across different cell types and developmental stages.