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Date of Award

Spring 2011

Author's School

College of Arts & Sciences

Author's Department/Program

Biology

Abstract

MicroRNAs (miRNAs) are a class of small RNAs that are known to be highly involved in post-transcriptional regulation in animals and plants. These short RNA sequences, usually between 21 and 24 nucleotides in length, are derived from longer, hairpin-containing transcripts, and work by binding to a target transcript and preventing it from being translated into protein. MiRNAs have recently been discovered in the unicellular green soil algae Chlamydomonas reinhardtii, contradicting the previously held belief that such activity was restricted to multicellular organisms. However, little is known about the specific roles of miRNA in Chlamydomonas. In this work, we hoped to classify some of these Chlamydomonas miRNAs of unknown function. We analyzed the in vivo activity of 6 pairs of putative miRNAs from different parts of the Chlamydomonas genome that accumulate between 2 and 8 hours after gametes fuse, which corresponds to the late-zygotic stage of Chlamydomonas’s life cycle. To do this, we designed a luciferase bioassay in which complementary sequences to two putative late zygotic miRNAs derived from the same transcript were placed in the 3’ untranslated region (UTR) of the luciferase gene. The constructs were placed under the control of a zygotic promoter and transformed into Chlamydomonas, and the resulting transformed colonies were analyzed for luciferase activity. In two of the 6 constructs that we analyzed, the change in luciferase activity between the vegetative and late zygotic stages was significantly smaller than that in the positive control, which did not contain putative miRNA targets. This implies that miRNAs do in fact suppress gene expression in Chlamydomonas during zygote development.

Language

English (en)