De Novo Synthesis of Sphingolipids Is Required for Cell Survival by Down-Regulating c-Jun N-Terminal Kinase in Drosophila Imaginal Discs

Abstract

Mitogen-activated protein kinase (MAPK) is a conserved eukaryotic signaling factor that mediates various signals, cumulating in the activation of transcription factors. Extracellular signal-regulated kinase (ERK), a MAPK, is activated through phosphorylation by the kinase MAPK/ERK kinase (MEK). To elucidate the extent of the involvement of ERK in various aspects of animal development, we searched for a Drosophila mutant which responds to elevated MEK activity and herein identified a lace mutant. Mutants with mild lace alleles grow to become adults with multiple aberrant morphologies in the appendages, compound eye, and bristles. These aberrations were suppressed by elevated MEK activity. Structural and transgenic analyses of the lace cDNA have revealed that the lace gene product is a membrane protein similar to the yeast protein LCB2, a subunit of serine palmitoyltransferase (SPT), which catalyzes the first step of sphingolipid biosynthesis. In fact, SPT activity in the fly expressing epitope-tagged Lace was absorbed by epitope-specific antibody. The number of dead cells in various imaginal discs of a lace hypomorph was considerably increased, thereby ectopically activating c-Jun N-terminal kinase (JNK), another MAPK. These results account for the adult phenotypes of the lace mutant and suppression of the phenotypes by elevated MEK activity: we hypothesize that mutation of lace causes decreased de novo synthesis of sphingolipid metabolites, some of which are signaling molecules, and one or more of these changes activates JNK to elicit apoptosis. The ERK pathway may be antagonistic to the JNK pathway in the control of cell survival.

Characterization of the Drosophila Sphingosine Kinases and Requirement for Sk2 in Normal Reproductive Function

“…4A). This pattern is also common to Sply (37,53) and lace (39,53) reflecting the functional relationship among these genes and suggesting the potential for coordinate gene regulation. Gut localization of SPL is also observed in C. elegans (38), suggesting that in simple metazoans gut tissues may comprise the major site of sphingolipid synthesis and clearance for the whole organism.…”

“…Disrupting sphingolipid synthesis through mutation of serine acyltransferase (lace) depletes endogenous long chain bases (LCBs) and phosphorylated long chain bases (LCBPs) and results in embryonic lethality. Hypomorphic alleles are associated with morphological abnormalities of the eye, wing, antennae, and bristles (39). LCB and LCBP accumulation caused by disrupting SPL (Sply) and the degradative pathway results in a different complement of phenotypes including cellspecific increases in embryonic and post-embryonic apoptosis, defects in adult muscle patterning, and reduced fecundity and viability.…”

Puckered‐GAL4 driving in JNK‐active cells

“…2c-j), although the P-element insertion sites in both puc GAL4E69 and puc E69 were identical. For example, in the eye disc, puc-lacZ expression was detected in the cells behind the morphogenetic furrow (Adachi-Yamada et al, 1999a). However, puc GAL4E69 was also expressed in cells at the anterior position (Fig.…”

Genetic elevation of Sphingosine 1-phosphate suppresses dystrophic muscle phenotypes in Drosophila

“…3G,I). We next used the UAS-lace transgenic fly line (Adachi-Yamada et al, 1999) to test for suppression of muscle degeneration. We reasoned that, when combined with tubulin-Gal4, the UAS-lace transgene could theoretically increase S1P levels by upregulating the expression of lace, the gene encoding the catalytic subunit of the first protein in the de novo synthesis pathway, serine palmitoyl CoA transferase (Fig.…”