De novo phytosterol synthesis in animals

Area of Science:

• Biochemistry
• Marine Biology
• Evolutionary Biology

Background:

• Sterols are essential lipids for eukaryotic cell membranes.
• Plants primarily synthesize phytosterols, while animals typically produce cholesterol.
• The distribution and synthesis of sterols vary significantly across different taxa.

Purpose of the Study:

• To investigate the sterol composition and synthesis in gutless marine annelids.
• To identify the specific enzymes and pathways involved in sterol production in these organisms.
• To understand the evolutionary implications of sterol synthesis in animals.

Main Methods:

• Multiomics analysis (genomics, transcriptomics, metabolomics).
• Metabolite imaging techniques.
• Heterologous gene expression and enzyme assays.
• Phylogenetic analysis of C-24 sterol methyltransferase (C24-SMT) genes.

Main Results:

• Sitosterol is the predominant sterol in gutless marine annelids.
• These annelids synthesize sitosterol de novo via a noncanonical C24-SMT.
• The C24-SMT enzyme, previously unknown in most bilaterian animals, was identified and characterized.
• Phylogenetic analyses showed C24-SMTs are present in at least five animal phyla.

Conclusions:

• Gutless marine annelids possess a unique pathway for de novo sitosterol synthesis.
• The presence of C24-SMTs in diverse animal phyla suggests a wider distribution of plant sterol synthesis in animals.
• This finding challenges the traditional view of sterol distribution between plants and animals.