Award Date

5-2010

Degree Type

Dissertation

Degree Name

Doctor of Philosophy in Biological Sciences

Department

Life Sciences

First Committee Member

J. Steven de Belle, Chair

Second Committee Member

Andrew Andres

Third Committee Member

Jeffery Shen

Fourth Committee Member

Allen Gibbs

Graduate Faculty Representative

Ron Gary

Number of Pages

241

Abstract

Mushroom bodies (MBs) are the site of multi modal sensory integration critical for associative conditioning in Drosophila. They have been central to research on the structure function relationship in the brain for over one hundred years due to their unique shape and readily accessible physiology. This dissertation incorporates three different approaches to further elucidate the genetic and molecular nature of this structure function relationship.

First, the suite of genetic and molecular tools available in Drosophila melanogaster, facilitated the molecular mapping of a 25-year old MB structural mutant called mushroom body miniature B (mbmB) to the gene Pendulin [Pen, also known as importin-!2 (imp-!2)]. Anatomical rescue, protein expression in the brain and functional domain analysis in mbmB mutants have shown that Imp-!2 is necessary for MB development, which likely gives rise to its learning, long term memory and amnesia resistant memory defects. Imp-!2 is a central component of nuclear cytoplasmic trafficking, mitotic spindle orientation, and injury response in the nervous system. The work described in this dissertation provides the first evidence that Imp-!2 also has a critical role in MB development and associative conditioning.

Second, MB specific Gal4 lines were used to identify novel genes associated with MB development through the identification of their flanking sequence. Ten Gal4 inserts were localized to introns, exons, and some intragenic regions of eight genes, likely to have interesting and testable roles in MB development and/or function. These candidate genes include: "FTZ-F1, Odorant receptor 42a, no extended memory, TAK1-associated binding protein, frizzled, Ecdysoneinduced protein 75B, Casein Kinase 1# and eyeless. Overall, the inserts themselves had minimal effects on MB development, likely due to their positions in non-coding regions. Protein levels in three homozygous MB Gal4 inserts, all found upstream of the frizzled gene, appeared reduced, indicating that these inserts can in fact disrupt protein levels independent of any effects they may or may not have on MB gross morphology. New evidence that genetic background influences MB anatomy is also provided through the analysis of two Gal4 lines in different genetic backgrounds. This work brings to light novel signaling pathways, likely associated with MB anatomy and development, that upon further investigation will aid in our understanding of the molecular nature of how the MBs form.

Finally, the influence of MBs on walking was investigated using mutant alleles of several genes with severe MB disruptions and a chemical method for MB ablation. Over the course of fifteen minutes (the initial stages of walking), flies with disrupted MBs showed a decrease in the frequency of walking indicating a role for MBs in the up-regulation of motor coordination during its initial stages. Slight differences in orientation to landmark and velocity were also observed, but attributed to pleiotropy rather than the MB disruptions. These findings were in contrast to conclusions made in previous work demonstrating MB’s involvement in the termination of walking bouts over longer time courses (i.e. MBs down-regulate locomotion). Both sets of data taken together implicate MBs in regulation of motor behaviors in a time dependent fashion, up regulating activity during the initial stages of walking, but suppressing activity thereafter. Therefore, MBs deliver appropriate contextual information to motor output centers in the brain by modifying the quantity of walking (activity) rather than the quality (velocity and orientation).

(Refer to PDF file for exact formulas.)

Keywords

Brains; Drosophila melanogaster; Fruit flies; Importin; MbmB; Mushroom bodies; Mutations; Walking

Disciplines

Molecular and Cellular Neuroscience

Language

English


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