Evolution of prokaryotic SPFH proteins

BACKGROUND: The SPFH protein superfamily is a diverse family of proteins whose eukaryotic members are involved in the scaffolding of detergent-resistant microdomains. Recently the origin of the SPFH proteins has been questioned. Instead, convergent evolution has been proposed. However, an independent, convergent evolution of three large prokaryotic and three eukaryotic families is highly unlikely, especially when other mechanisms such as lateral gene transfer which could also explain their distribution pattern have not yet been considered.To gain better insight into this very diverse protein family, we have analyzed the genomes of 497 microorganisms and investigated the pattern of occurrence as well as the genomic vicinity of the prokaryotic SPFH members. RESULTS: According to sequence and operon structure, a clear division into 12 subfamilies was evident. Three subfamilies (SPFH1, SPFH2 and SPFH5) show a conserved operon structure and two additional subfamilies are linked to those three through functional aspects (SPFH1, SPFH3, SPFH4: interaction with FtsH protease). Therefore these subgroups most likely share common ancestry. The complex pattern of occurrence among the different phyla is indicative of lateral gene transfer. Organisms that do not possess a single SPFH protein are almost exclusively endosymbionts or endoparasites. CONCLUSION: The conserved operon structure and functional similarities suggest that at least 5 subfamilies that encompass almost 75% of all prokaryotic SPFH members share a common origin. Their similarity to the different eukaryotic SPFH families, as well as functional similarities, suggests that the eukaryotic SPFH families originated from different prokaryotic SPFH families rather than one. This explains the difficulties in obtaining a consistent phylogenetic tree of the eukaryotic SPFH members. Phylogenetic evidence points towards lateral gene transfer as one source of the very diverse patterns of occurrence in bacterial species

Reggie-1/flotillin-2 promotes secretion of the long-range signalling forms of Wingless and Hedgehog in Drosophila

The lipid-modified morphogens Wnt and Hedgehog diffuse poorly in isolation yet can spread over long distances in vivo, predicting existence of two distinct forms of these mophogens. The first is poorly mobile and activates short-range target genes. The second is specifically packed for efficient spreading to induce long-range targets. Subcellular mechanisms involved in the discriminative secretion of these two forms remain elusive. Wnt and Hedgehog can associate with membrane microdomains, but the function of this association was unknown. Here we show that a major protein component of membrane microdomains, reggie-1/flotillin-2, plays important roles in secretion and spreading of Wnt and Hedgehog in Drosophila. Reggie-1 loss-of-function results in reduced spreading of the morphogens, while its overexpression stimulates secretion of Wnt and Hedgehog and expands their diffusion. The resulting changes in the morphogen gradients differently affect the short- and long-range targets. In its action reggie-1 appears specific for Wnt and Hedgehog. These data suggest that reggie-1 is an important component of the Wnt and Hedgehog secretion pathway dedicated to formation of the mobile pool of these morphogens