Drosophila p24 homologues eclair and baiser are necessary for the activity of the maternally expressed Tkv receptor during early embryogenesis

Abstract

p24 proteins are assumed to play an important role in the transport of secreted and transmembrane proteins into membranes. However, only few cargo proteins are known that partially, but in no case completely require p24 proteins for membrane transport. Here, we show that two p24 proteins are essential for dorsoventral patterning of Drosophila melanogaster embryo. Mutations in the genes, eclair (eca) and baiser (bai), encoding two p24 proteins reduce signalling by the TGF-beta homologue, Dpp, in early embryos. This effect is strictly maternal and specific to early embryogenesis, as Dpp signalling in other contexts is not notably affected. We provide genetic evidence that in the absence of eca or bai function in the oocyte, the maternally expressed type I TGF-beta receptor Tkv is not active. We propose that during early embryogenesis eca and bai are specifically required for the activity of the maternal Tkv, while the zygotic Tkv is not affected in the mutant embryos. Mutations in either eca or bai are sufficient for the depletion of Tkv activity and no enhancement of the phenotypes was observed in embryos derived from oocytes mutant for both genes. The dependence of maternal Tkv protein on the products of p24 genes may serve as an in vivo model for studying p24 proteins.

Drosophila melanogasterp24 genes have developmental, tissue‐specific, and sex‐specific expression patterns and functions

“…Our data on loj (Carney and Taylor, 2003) and CG31787 (Table 1), as well as previous work on the eca and bai genes (Bartoszewski et al, 2004), indicate that some widely expressed p24 genes have sex-specific functions; mutations in loj, eca, and bai have apparent phenotypic consequences only in females (Carney and Taylor, 2003;Bartoszewski et al, 2004). Because we have shown that particular p24 genes have developmental, tissue-specific, or transcript-specific expression patterns (Table 1; Fig.…”

“…The developmental or tissue-specific profiles of p24 genes and proteins in multicellular organisms have not been extensively determined (Kawabe et al, 1999;Wen and Greenwald, 1999;Denzel et al, 2000;Kuiper et al, 2000;Rötter et al, 2002;Carney and Taylor, 2003;Bartoszewski et al, 2004). Because members of the p24 family may function together to provide different cargo or vesicle specificities (Marzioch et al, 1999;, an important first step in understanding their functions is to identify the p24 genes and proteins that are coexpressed within tissues.…”

“…Because there are data suggesting that p24 proteins function as heterotetramers (Marzioch et al, 1999), we propose that loj functions with eca and bai, which have expression patterns (Table 1; Fig. 2) and mutant phenotypes similar to loj (Bartoszewski et al, 2004), in the CNS to regulate oviposition behavior. These proteins represent three of the four p24 protein lineages (Carney and Bowen, 2004).…”

“…p24 proteins also are proposed to function in folding or other types of posttranslational modification (Bartoszewski et al, 2004), membrane organization (Rojo et al, 1997Lavoie et al, 1999;Emery et al, 2003), and in vesicle formation and budding (Stamnes et al, 1995;Elrod-Erickson and Kaiser, 1996;Bremser et al, 1999).…”

Apoptosis-linked Gene-2 (ALG-2)/Sec31 Interactions Regulate Endoplasmic Reticulum (ER)-to-Golgi Transport

“…7C). p24 cycles between the ER and Golgi, is a major component of both COPII and COPI vesicles (50), serves as a primer for COPI vesicle formation (51,64), and, in isoform-specific fashion, appears to serve as a cargo receptor for glycosylphosphatidylinositol-anchored proteins (65,66), G-protein coupled receptors (67), and the Wnt ligand wingless (68,69). Proper p24 trafficking and interaction with other binding partners requires hetero-oligomerization among several closely related p24 family isoforms (70 -72).…”