Organelle transport of RNA during early embryonic development

Abstract

During the early stages of development, regulation of RNA localization is critical for a newly fertilized embryo. The regulation of localized RNA allows for proper cell division. We have previously found RNAs localize to the mitotic spindles in both sea urchin embryos (Strongylocentrotus purpuratus) and mammalian cell lines. We have further demonstrated that forcing translation of spindle-enriched Fascin mRNA to occur at the cell periphery results in chromosomal segregation defects, developmental delay, and embryonic lethality. Thus, proper transport of RNA, including Fascin and Rab35, to the mitotic spindle is critical for proper development. How these RNAs get transported to the mitotic spindle is not understood. Prior studies have shown that miRNAs and RNAs can be subcellularly trafficked via hitchhiking with organelles, such as lysosomes, mitochondria, and multivesicular bodies (MVBs). We hypothesize that RNAs, including spindle-enriched Fascin and Rab35, hitchhike on organelles from cytosol to the mitotic spindle. To test this hypothesis, we examine localization and distribution of organelles, including early endosomes, mitochondria, and lysosomes during mitosis. Data indicate that early endosomes are enriched in the cytoplasmic region. Although lysosomes and mitochondria are ubiquitously present in all subcellular region of the early cleavage stage embryonic blastomere, they are enriched in the cytoplasm. To further test our hypothesis, we use single molecule resolution imaging to examine co-transport of Fascin mRNA and mitochondria. Preliminary data indicate that some Fascin mRNA and mitochondria co-localize and co-transport in the early cleavage stage sea urchin embryo. This work provides insight into novel mechanisms of how RNA can be transported to the mitotic spindle for local translation, when the embryo undergoes rapid cell divisions.