Date of Award

Spring 1-1-2014

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

First Advisor

Min Han

Second Advisor

Ding Xue

Third Advisor

Greg Odorizzi

Fourth Advisor

Michael Stowell

Fifth Advisor

XueDong Liu

Abstract

The functional consequences of extensive lipid molecule variation, including fatty acids, on cellular and developmental functions are poorly understood. Monomethyl branched-chain fatty acids (mmBCFAs) are present in multiple organisms including mammals, however the functional specificities associated with this group of fatty acids in mammals are essentially unknown. In recent years, C. elegans has emerged as a premier model system to study mmBCFAs and their derived lipids, mainly due to the availability of genetic tools to specifically block the de novo synthesis of mmBCFAs and the ability to manipulate mmBCFAs in the diet. Pervious work has identified key enzymes/factors in mmBCFA biosynthesis and feedback-regulatory pathways and has shown that mmBCFAs are essential for postembryonic development.

To understand how mmBCFAs impact development in C. elegans, I performed a genetic screen for suppressors of the developmental defect caused by mmBCFA-depletion. Extensive characterization of one suppressor identified the suppressing role of prx-5, which encodes a receptor for the type-1 peroxisomal-targeting-signal proteins. I found that disrupting prx-5 function compromised the import of peroxisomal matrix proteins, increased mmBCFA C17ISO level in animals with defective mmBCFA synthesis, and consequently restored wild-type development. Further analysis also suggests that a novel peroxisome-related mechanism is involved in mmBCFA homeostasis. Thus, this study reveals a novel connection between peroxisomal protein transportation and mmBCFA metabolism.

A previous parallel study has indicated that an mmBCFA-containing glucosylceramide (d17iso-GlcCer) mediates mmBCFA function in postembryonic development by activating the TORC1 signaling pathway. The NPRL-2/3 complex represses this d17iso-GlcCer-TORC1 function. To understand how the NPRL-2/3 complex affects this function, I searched for components that interact with NPRL-2 by performing co-immunoprecipitation. Among ~40 candidates, GSK-3 and PPTR-2 appear to partially mediate the repressive impact of NPRL-2 on development. In addition, 15 other NPRL-2 interactors may potentially act positively in d17iso-GlcCer-TORC1 pathway. Further studies may provide valuable insights into the complex regulatory pathway involving mmBCFAs.

This thesis represents part of the overall efforts to understand the mechanism of mmBCFA functions in animal development and behaviors. The accumulated knowledge on this particular fatty acid variant may significantly contribute to our understanding of how different lipids can impact specific physiological functions.

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