The ceramide synthase 2b gene mediates genomic sensing and regulation of sphingosine levels during zebrafish embryogenesis.

Abstract

Sphingosine-1-phosphate (S1P) is generated through phosphorylation of sphingosine by sphingosine kinases (Sphk1 and Sphk2). We show that <i>sphk2</i> maternal-zygotic mutant zebrafish embryos (<i>sphk2^MZ</i>) display early developmental phenotypes, including a delay in epiboly, depleted S1P levels, elevated levels of sphingosine, and resistance to sphingosine toxicity. The <i>sphk2^MZ</i> embryos also have strikingly increased levels of maternal transcripts encoding ceramide synthase 2b (Cers2b), and loss of Cers2b in <i>sphk2^MZ</i> embryos phenocopies sphingosine toxicity. An upstream region of the <i>cers2b</i> promoter supports enhanced expression of a reporter gene in <i>sphk2^MZ</i> embryos compared to wildtype embryos. Furthermore, ectopic expression of Cers2b protein itself reduces activity of the promoter, and this repression is relieved by exogenous sphingosine. Therefore, the <i>sphk2^MZ</i> genome recognizes the lack of sphingosine kinase activity and up-regulates <i>cers2b</i> as a salvage pathway for sphingosine turnover. Cers2b can also function as a sphingolipid-responsive factor to mediate at least part of a feedback regulatory mechanism.