Drosophila Signal Peptidase Complex Member Spase12 Is Required for Development and Cell Differentiation

Abstract

It is estimated that half of all proteins expressed in eukaryotic cells are transferred across or into at least one cellular membrane to reach their functional location. Protein translocation into the endoplasmic reticulum (ER) is critical to the subsequent localization of secretory and transmembrane proteins. A vital component of the translocation machinery is the signal peptidase complex (SPC) - which is conserved from yeast to mammals – and functions to cleave the signal peptide sequence (SP) of secretory and membrane proteins entering the ER. Failure to cleave the SP, due to mutations that abolish the cleavage site or reduce SPC function, leads to the accumulation of uncleaved proteins in the ER that cannot be properly localized resulting in a wide range of defects depending on the protein(s) affected. Despite the obvious importance of the SPC, in vivo studies investigating its function in a multicellular organism have not been reported. The Drosophila SPC comprises four proteins: Spase18/21, Spase22/23, Spase25 and Spase12. Spc1p, the S. cerevisiae homolog of Spase12, is not required for SPC function or viability; Drosophila spase12 null alleles, however, are embryonic lethal. The data presented herein show that spase12 LOF clones disrupt development of all tissues tested including the eye, wing, leg, and antenna. In the eye, spase12 LOF clones result in a disorganized eye, defective cell differentiation, ectopic interommatidial bristles, and variations in support cell size, shape, number, and distribution. In addition, spase12 mosaic tissue is susceptible to melanotic mass formation suggesting that spase12 LOF activates immune response pathways. Together these data demonstrate that spase12 is an essential gene in Drosophila where it functions to mediate cell differentiation and development. This work represents the first reported in vivo analysis of a SPC component in a multicellular organism.

Transmembrane proteins – Mining the cattle tick transcriptome

“…This complex contains four subunits and has been found to be involved in the initiation of protein translocation (Fons et al, 2003), as well as the accelerated degradation of misfolded proteins (Nagasawa et al, 2007). A transmembrane signal peptidase (SP) and oligosaccharyltransferase (OST) complex is involved in cleaving off the signal peptide of proteins and to glycosylate the polypeptide, respectively (Mohorko et al, 2011;Haase Gilbert et al, 2013). One of the subunits of the SP complex has been newly identified in this study (Contig2157), as well as four subunits of the OST complex (Contig5725, 1356, 4332 and 1719) ( Table 2) which were, however, all previously identified in other publications in R. microplus in addition to R. sanguineus and Ornithodoros moubata for Contigs4332 and 1719 (Diaz-Martin et al, 2013;Oliveira et al, 2013).…”

ER type I signal peptidase subunit (LmSPC1) is essential for the survival of Locusta migratoria manilensis and affects moulting, feeding, reproduction and embryonic development

“…As was observed with LmSPC1, obvious moulting defects occurred when genes related to the components of the secretion machinery of this process were inactivated (Frand et al ., ). The crippled wings observed after moulting in RNAi‐injected locust nymphs are similar to those observed in Drosophila with mutated Spase12, another subunit of the ER type I signal peptidase (Gilbert et al ., ).…”

“…A vertebrate has more than 100 different types of cells, and many cells form very organized patterns to perform their specialized functions (Lodish et al ., ). However, the functions of ER type I signal peptidases in animals have only been described in the animal model Drosophila ; in these organisms, the subunit Spase12 was disrupted (Gilbert et al ., ), but essential catalytic subunits were not identified.…”

Analysis of the functions of the signal peptidase complex in the midgut of Tribolium castaneum

“…In Drosophila melanogaster , four signal peptidase genes exist: Spase12 , Spase18/21 , Spase22/23 , and Spase25 (Abrams & Andrew, ). In Drosophila , a loss‐of‐function assay of Spase12 demonstrated that this gene causes defects in all of the tissues tested (Haase Gilbert, Kwak, Chen, & Mardon, ). In Drosophila , cell differentiation in the eyes was flawed if Spase12 was lost.…”

“…However, it is unclear whether there is any change with the adult midgut development if Spase18/21 was knocked down. Melanotic masses were observed in Spase12 mutant flies (Haase Gilbert et al., ), indicating that the loss of Spase12 likely activates the immune response pathway. Besides the studies as described above, we do not know the function of SPC in other insects including their importance to development.…”