Plasma Membrane Protein Nce102 Modulates Morphology and Function of the Yeast Vacuole.

Membrane proteins are targeted not only to specific membranes in the cell architecture, but also to distinct lateral microdomains within individual membranes to properly execute their biological functions. Yeast tetraspan protein Nce102 has been shown to migrate between such microdomains within the plasma membrane in response to an acute drop in sphingolipid levels. Combining microscopy and biochemistry methods, we show that upon gradual ageing of a yeast culture, when sphingolipid demand increases, Nce102 migrates from the plasma membrane to the vacuole. Instead of being targeted for degradation it localizes to V-ATPase-poor, i.e., ergosterol-enriched, domains of the vacuolar membrane, analogous to its plasma membrane localization. We discovered that, together with its homologue Fhn1, Nce102 modulates vacuolar morphology, dynamics, and physiology. Specifically, the fusing of vacuoles, accompanying a switch of fermenting yeast culture to respiration, is retarded in the strain missing both proteins. Furthermore, the absence of either causes an enlargement of ergosterol-rich vacuolar membrane domains, while the vacuoles themselves become smaller. Our results clearly show decreased stability of the V-ATPase in the absence of either Nce102 or Fhn1, a possible result of the disruption of normal microdomain morphology of the vacuolar membrane. Therefore, the functionality of the vacuole as a whole might be compromised in these cells.

Phylogeny of Lasius ants based on mitochondrial DNA and morphology, and the evolution of social parasitism in the Lasiini (Hymenoptera: Formicidae).

Phylogeny of ants of the tribe Lasiini (Lasius, Acanthomyops, Prenolepis, Euprenolepis, Paratrechina, Pseudolasius, and Myrmecocystus) was analysed using 81 morphological, ecological, and behavioural characters (for 41 species) and mitochondrial DNA sequences (COI, COII, tRNA-Leu; for 19 species). The free-living subgenus Lasius s. str. is paraphyletic with respect to the rest of genus; the traditional "genus" Acanthomyops should be considered a part of Lasius s. lat.; free-living subgenus Cautolasius is a member of the clade of socially parasitic Lasius ants (=Chtonolasius+Acanthomyops+Austrolasius+Dendrolasius). The tree topology is congruent with two alternative scenarios of origin of the temporary social parasitism: (i) a single origin of the parasitic strategy in a derived subclade of Lasius and a secondary loss of this trait in Cautolasius, (ii) a parallel origin of the social parasitism within the clade of hypogeic Lasius ants (in Chtonolasius, and in Acanthomyops+Dendrolasius+Austrolasius). Emery's rule in the strict sense does not apply to this group because most parasites exploit any ecologically available, even phylogenetically distant host species. The parasitic strategy in Lasius could have originated from the aggressive interactions between cofounding queens during pleometric colony founding and/or from the secondary queen adoption.