Biosynthetic studies of marine lipid 35. The demonstration of de novo sterol biosynthesis in sponges using radiolabeled isoprenoid precursors

Sterol and genomic analyses validate the sponge biomarker hypothesis

“…But here the transcriptomes are informative, as SMT genes from putative eukaryotic symbionts living in sponge tissues should have been recovered alongside the sponge genes. This interpretation is also contradicted by significant research demonstrating that demosponges perform de novo sterol synthesis and side chain alkylation (23,26) and that sterol patterns do not differ dramatically within species collected from different locations or times (19). The protocols used to generate the transcriptomes involved the enrichment of eukaryotic mRNAs (20), meaning that genes from prokaryotic symbionts could have been lost.…”

Biosynthesis of marine sterols

“…No single template will suffice for marine sterols; three sub-structures (4-6) for sterol nuclei have been proposed by Djerassi [7] to describe the marine monohydroxy sterols, and these nuclei are accompanied by a wide spectrum of side-chains (7-91) (Fig. t); perhaps the most intriguing marine sterols include cyclopropane (10, 11) -and cyclopropene (12,13) -containing sterols (Fig. 2) and the biosynthetically related acetylenes (14,15).…”

“…The number of organisms which have been shown to be capable of de novo biosynthesis is quite large; in fact it has recently been suggested that all sponges are capable of de novo biosynthesis of sterols [12,13]. The early biosynthetic studies utilizing acetate (22) and mevalonate (23) [3,12,14] resulted in ambiguous results; these ambiguities turn out to be a result of the nature of working with these water-soluble precursors.…”

“…The early biosynthetic studies utilizing acetate (22) and mevalonate (23) [3,12,14] resulted in ambiguous results; these ambiguities turn out to be a result of the nature of working with these water-soluble precursors. Djerassi has suggested I7, 13] that poor uptake or alternate metabolism of these water-soluble precursors, and not their (26) inability to perform de novo sterol biosynthesis has accounted for many of the inconclusive or negative results and that lipid precursors, such as squalene (26), are better suited for investigation of de novo sterol biosynthesis.…”

“…The incorporation of sterol precur- (26) in photosynthetic and non-photosynthetic organisms sors into crustaceans has yet to be demonstrated [5,16]. The red alga Rhodymenia palmata [17] can incorporate acetate (22) and mevalonate (23).…”