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Characterization of Volvocine Sphingolipid Metabolism
Sphingolipids are membrane lipids found predominantly in eukaryotic life. They have been implicated to be important in the development of multicellularity and cellular differentiation. A collection of freshwater, green microalgae known as the volvocine algae are a model of simple multicellularity and cellular differentiation. The volvocine algae include Chlamydomonas (single celled, undifferentiated) and Volvox (multicellular, differentiated), and others with intermediate complexity varying in cell number, colony size, extracellular matrix (ECM) content, and degree of differentiation. In this work, glycosphingolipids were investigated for their importance to volvocine algal development and in relation to the differences in volvocine characteristics. Sphingolipid structures were characterized and quantified using HPLC-MS/MS, and volvocine algae were treated with different inhibitors to probe the roles of sphingolipids for each volvocine algae to determine the relationship between glycosphingolipids and simple multicellularity, cellular differentiation, or development. The neutral glycosphingolipid glucosylceramide was found to contain a novel α-hydroxylated 18:2Δ9,12 fatty acid in each volvocine algae, and is more abundant in gonidia of Volvox colonies. Inhibition of glucosylceramide synthase resulted in hollow, malformed gonidia, while Chlamydomonas showed no difference to inhibition of glucosylceramide synthase. Characterization of glycosylinositolphosphoceramides (GIPCs) from each of the volvocine algae used in this work found each possessed a unique glycan headgroup that increased in complexity with increasing volvocine complexity. Each of the characterized volvocine GIPC contained a conserved di-hexose glycan branch, and algae with expanded ECM also contained a pentose side branch in the glycan headgroup. More complex volvocine algae had less GIPC overall but more nucleotide sugars than less complex volvocine algae. Treatment of Chlamydomonas with myriocin was non-lethal and resulted in gross morphological defects in its morphology. An engineered Saccharomyces yeast strain was created to produce plant/algal-like sphingolipids as a tool for future research discovering novel enzymes involved in sphingolipid metabolism, such as glycosyltransferases synthesizing glycosphingolipids. The unique glucosylceramides and diversity in GIPC glycan headgroups of volvocine GIPCs suggests glycosphingolipids may play an important role in simple multicellularity, cellular differentiation, and development.
Romsdahl, Trevor B, "Characterization of Volvocine Sphingolipid Metabolism" (2017). ETD collection for University of Nebraska - Lincoln. AAI10690895.