Date of Degree
PhD (Doctor of Philosophy)
First Committee Member
Second Committee Member
Third Committee Member
Fourth Committee Member
Johnson, Wayne A.
Lithium has been used for more than 50 years as a primary therapy for bipolar affective disorder (BPD) and has proven highly effective for both acute and long-term phases of the disease. Unfortunately, the molecular and cellular mechanisms underlying the mood-stabilizing action of lithium for the treatment of BPD remains largely unknown. In an effort towards understanding the complexities of lithium's action in the nervous system, I have utilized the Drosophila neurological mutant Shudderer (Shu). Previous findings have suggested that the adult Shu phenotypes may be improved by providing a diet containing millimolar concentrations of lithium.
Using well-established genetic techniques and behavioral paradigms I thoroughly characterized the Shu mutant phenotypes. I found that the mutant displays morphological and behavioral abnormalities indicative of dysregulated neuronal excitability that include: down-turning wings and indented dorsal thorax, defects in negative geotaxis, deficits in locomotion, abnormal sleep architecture and unusual patterns of leg-shaking behaviors upon recovery of ether anesthetics. Furthermore, I confirmed that lithium was able to significantly improve many aspects of Shu behaviors.
Recombination-based mutation mapping in Shu revealed that the genetic lesion lies somewhere within the gene CG9907, which encodes the voltage-gated sodium channel á-subunit paralytic (para). Subsequent genetic experiments using para hypomorphic mutant alleles as well as a UAS-RNAi/GAL4 system showed that a reduction in sodium channel levels resulted in a drastic improvement of the mutant defects. Together, these data suggest that the lithium-responsive Shu mutant is likely a gain-of-function allele of para. Sequencing of the entire para coding region identified a missense mutation in a highly conserved region of the para coding sequence, in transmembrane segment S2 of homology domain III ((M1350I). To date, this is the first known discovery of a sodium channel mutant allele in Drosophila which causes hyperactivity. These data suggest that the Shu phenotypes are somehow caused by an increase in sodium channel activation.
Lastly, I identified a number of genes likely to functionally interact with the Shu mutation. Of note, the Ca2+/calmodulin-activated Ser/Thr protein phosphatase alpha subunit gene CanA-14F is up-regulated in Shu and reduction of its activity suppresses the mutant phenotypes. Furthermore, a large percentage of genes encoding anti-microbial peptides (AMP) were also significantly up-regulated in Shu, possibly acting downstream of CanA-14F. A genetic deficiency screen looking for genes that alter the Shu phenotypes has identified that the gene Glutathione S-transferase S1 (Gsts1) suppresses the morphological and behavioral defects in the lithium-responsive mutant. Overall, these genes will help decipher how the gain-of-function sodium channel Shu mutation alters nervous system function. In addition, they will shed light on those mechanisms responsible for lithium's mood-stabilizing effects in the brain.
behavior, drosophila, GSK3-beta, lithium, para, sodium channel
xv, 152 pages
Includes bibliographical references (pages 135-152).
Copyright 2010 Garrett Anthony Kaas
Kaas, Garrett Anthony. "Genetic analysis of Shudderer, the lithium-responsive neurological mutant of Drosophila melanogaster." PhD (Doctor of Philosophy) thesis, University of Iowa, 2010.