A compendium of expression patterns of cholesterol biosynthetic enzymes in the mouse embryo

Abstract

Cholesterol and its biosynthetic pathway intermediates and derivatives are required for many developmental processes including membrane biogenesis, transmembrane receptor signaling, steroid biogenesis, nuclear receptor activation, and posttranslational modification of hedgehog (Hh) proteins. To perform such multifaceted tasks depends on stringent regulation of expression of cholesterol biosynthetic enzymes (CBEs). We established for a whole organism, for the first time, the 3D expression pattern of all genes required for cholesterol biosynthesis (CBS), starting from acetyl-CoA and ending with cholesterol. This data was produced by high-throughput in situ hybridization on serial sections through the mouse fetus. The textually annotated image data were seamlessly integrated into the METscout and GenePaint public databases. This novel information helps in the understanding of why CBEs are expressed at particular locations within the fetus. For example, strong CBE expression is detected at sites of cell proliferation and also where cell growth increases membrane surface, such as in neurons sprouting axons and forming synapses. The CBE data also sheds light on the spatial relationship of cells and tissue that express sonic Hh (Shh) and produce cholesterol, respectively. We discovered that not all cells expressing Shh are capable of CBS. This finding suggests novel ways by which cholesterylation of Shh is regulated. Cholesterol and its biosynthetic pathway intermediates and derivatives are required for many developmental processes including membrane biogenesis, transmembrane receptor signaling, steroid biogenesis, nuclear receptor activation, and posttranslational modification of hedgehog (Hh) proteins. To perform such multifaceted tasks depends on stringent regulation of expression of cholesterol biosynthetic enzymes (CBEs). We established for a whole organism, for the first time, the 3D expression pattern of all genes required for cholesterol biosynthesis (CBS), starting from acetyl-CoA and ending with cholesterol. This data was produced by high-throughput in situ hybridization on serial sections through the mouse fetus. The textually annotated image data were seamlessly integrated into the METscout and GenePaint public databases. This novel information helps in the understanding of why CBEs are expressed at particular locations within the fetus. For example, strong CBE expression is detected at sites of cell proliferation and also where cell growth increases membrane surface, such as in neurons sprouting axons and forming synapses. The CBE data also sheds light on the spatial relationship of cells and tissue that express sonic Hh (Shh) and produce cholesterol, respectively. We discovered that not all cells expressing Shh are capable of CBS. This finding suggests novel ways by which cholesterylation of Shh is regulated. Embryogenesis is characterized by significant mass increase which is caused by cell proliferation and cell growth, both of which depend on continuous production of cellular membranes. Because such membranes contain up to 20 weight percent cholesterol, availability of this compound is essential for embryogenesis. Cholesterol maintains membrane integrity and also contributes to and regulates the properties of lipid rafts and lipid microdomains. Rafts and microdomains are the sites where many transmembrane signaling processes occur that play pivotal roles in development (1.Woollett L.A. Where does fetal and embryonic cholesterol originate and what does it do?.Annu. Rev. Nutr. 2008; 28: 97-114Crossref PubMed Scopus (56) Google Scholar, 2.Porter F.D. Herman G.E. Malformation syndromes caused by disorders of cholesterol synthesis.J. Lipid Res. 2011; 52: 6-34Abstract Full Text Full Text PDF PubMed Scopus (335) Google Scholar). Cholesterol also has very direct effects. It is covalently bound to the N-terminal fragment of hedgehog (Hh) proteins, and has essential roles in pattern formation and morphogenesis in invertebrates