A flexible sterol metabolism in Capsaspora owczarzaki has features that resemble both fungi and animals.

NAJLE S.; UTTARO AD; RUIZ-TRILLO I

Giens

Congreso; The origin of metazoans-Spongex program; 2015

Sterols are essential for several physiological processes in most eukaryotes, including ani-mals. They play a key role in regulating membrane uidity and permeability and participatein dierent signal transduction pathways as precursors of steroid hormones and vitamins.Sterols are also fundamental in the formation of lipid rafts, regions of reduced uidity thatselectively incorporate proteins involved in concerted functions such as cell-cell recognition,adhesion and communication. All of these cellular processes are crucial for the developmentand homeostasis of multicellular organisms. Sterols conform one of the most diverse fam-ilies of molecules in nature, and much of this diversity is found in non-bilaterian animals.Nevertheless, among the opisthokonts, two major types of sterols prevail. Vertebrates arecharacterized by having a 27-carbon (C27) sterol, namely cholesterol, as their main sterolcomponent. On the other hand, Fungi are characterized by possessing mainly ergosterol(C28). However, information on the sterol metabolism in unicellular holozoans is scarceand so we lack a good understanding on how lipid metabolism evolved in both animals andfungi. To address this, we characterized the sterols metabolism in the lasterean Capsas-pora owczarzaki, a close unicellular relative of animals. We found that the genome of C.owczarzaki encodes the complete set of genes for the canonical synthesis pathway of ergos-terol, typical of Fungi, as well as an ortholog of the Rieske sterol C7(8)-desaturase, absentin Fungi and highly conserved in animals. Importantly, RNAseq data indicates a dierentialtranscriptional regulation of this metabolism between dierent life stages in C. owczarzaki.This was further conrmed by using radioactive precursors and biochemical analyses. More-over, we identied a novel sterol synthesis pathway in C. owczarzaki, which is being deployeddierentially in the dierent life stages. Thus, in the lopodial and aggregative stages C.owczarzaki converts the cholesterol from the growth medium into ergosterol using this previ-ously un-described synthesis pathway. On the other hand, in the cystic stage, de novo sterolsynthesis leads to the production of 7-dehydrocholesterol as end product. We hypothesizethat the membranes of C. owczarzaki alternate between animal-like and fungal-like sterolsacross its life cycle, suggesting a very versatile lipid metabolism which turns this species intoa good model to study the requirements for each sterol and within the context of opisthokontevolution.