Localization of maternal mRNAs is an important developmental strategy for providing spatially restricted synthesis of the encoded proteins. Much of the work done on localized RN As in Drosophila development has focused on identification of pattern determinants, but not all localized maternal RNAs encode such patterning specifiers. Adducin-like, also known as hu-li tai shao, represents the only example to date of a transcript which is both localized throughout Drosophila oogenesis and encodes a cytoskeletal protein. Adducin-like encodes the Drosophila homologue of mammalian adducin, which in humans is a membrane-cytoskeletal protein that contributes to local cytoskeletal assembly, particularly at sites of cell-cell contact and communication. We show here that Adducin-like generates a family of transcripts through alternative mRNA splicing. The splice variants of Adducin-like share sequence in the open reading frame (ORF) but are truncated at different points and have unique 3' ORF sequences plus different 3'UTRs. One of these transcript classes, R1, encodes an Adducin-like protein isoform with a MARCKS-related element and represents the first Drosophila orthologue of mammalian adducin. R1 Adducin-like activity is likely to be regulated by signal transduction pathways similar to those affecting human adducins. Another Adducin-like transcript class, N4, is localized specifically to and within the developing Drosophila oocyte and early embryo. Cis-acting signals for N4 RNA localization are contained within the 3'UTR. We have mapped these signals and identified a unique cis-acting element capable of directing early transport of mRNA into the oocyte. swallow is required for the localization of Adducin-like mRNA, and we present evidence that swallow acts through the Adducin-like N4 3'UTR to promote Adducin-like N4 mRNA localization in mid- to late oogenesis. We consider the possible functions of alternative splicing in development. Another non-pattern-specifying maternal RNA localized in early Drosophila development is the mitochondrial 16S large ribosomal RNA (16S RNA). The 16S RNA is localized to the posterior of the early embryo and appears to be a constituent of polar granules, since maternal effect mutations which disrupt the polar granules also abolish 16S RNA localization. We show that 16S RNA localization does not appear to be necessary for pole cell formation or function.
Kellie Lynn Whittaker (Thu,) studied this question.