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Description:
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It has been proposed that the various 14 -3 -3 isotypes and isoforms present in all eukaryotes are largely functionally equivalent . However , this is not consistent with the conservation of multiple isoforms and isotypes , especially in vertebrates with seven 14 -3 -3 encoding genes and nine isotypes . The hypothesis tested in this thesis is that both isoform -specific and overlapping functions are likely mediated through tissue specific expression , colocalization and dimerization of 14 -3 -3 proteins occur in vivo . Drosophila melanogaster was selected because it offers a simple , but representative system to study these proteins functionally . This thesis focuses primarily on D14 -3 -3 ? , although the expression pattern and phenotypes associated with all three Drosophila 14 -3 -3s were determined . I first determined the expression pattern of the three different 14 -3 -3 isotypes (leoI , leoII and D14 -3 -3 ? ) and described developmental phenotypes associated with mutations in 14 -3 -3 isotypes in Drosophila . I found that there is partial redundancy with respect to lethality . Both LEO and D14 -3 -3 ? appear required for normal germ -line and somatic gonadal development . However , they do not appear to be functionally equivalent with respect to this phenotype since LEO is unable to compensate for the loss of D14 -3 -3 ? . I also determined that D14 -3 -3 ? mutants have unique phenotypes including deficits in adult cross -vein formation and rapid habituation to olfactory and footshock stimuli . To further understand the unique role that D14 -3 -3 ? plays in the adult CNS , I mapped the areas in the brain involved in olfactory and footshock habituation . I found that although the mushroom bodies (MBs ) are necessary to inhibit premature habituation such as that exhibited by D14 -3 -3 ? mutants , D14 -3 -3 ? expression specifically in the MBs is not sufficient to rescue premature habituation . Although the loss of either LEO or D14 -3 -3 ? appears to cause a deficit in olfactory associative learning , premature habituation is the cause of the deficit seen in D14 -3 -3 ? mutants . As leo mutants do not exhibit a premature habituation phenotype , it appears that within the MBs LEO and D14 -3 -3 ? are not functionally equivalent . Therefore , the data supports the hypothesis that 14 -3 -3s have functional specificity and redundancy likely to represent use of homo and heterodimers in different processes within the tissues of an organism . |