SummarySexual development in fungi is a complex process involving the generation of new cell types and tissues -an essential step for all eukaryotic life. The characterization of sterile mutants in the ascomycete Sordaria macrospora has led to a number of proteins involved in sexual development, but a link between these proteins is still missing. Using a combined tandem-affinity purification/mass spectrometry approach, we showed in vivo association of developmental protein PRO22 with PRO11, homologue of mammalian striatin, and SmPP2AA, scaffolding subunit of protein phosphatase 2A. Further experiments extended the protein network to the putative kinase activator SmMOB3, known to be involved in sexual development. Extensive yeast two-hybrid studies allowed us to pinpoint functional domains involved in protein-protein interaction. We show for the first time that a number of already known factors together with new components associate in vivo to form a highly conserved multi-subunit complex. Strikingly, a similar complex has been described in humans, but the function of this so-called striatin interacting phosphatase and kinase (STRIPAK) complex is largely unknown. In S. macrospora, truncation of PRO11 and PRO22 leads to distinct defects in sexual development and cell fusion, indicating a role for the fungal STRIPAK complex in both processes.
The goal of this review is to highlight what little is known, and point to the bulk of what is yet to be learned, about the natural history of placozoans in the field-in order to stimulate a broader search for placozoans and a fuller exploration of their distribution, diversity, and all other aspects of their enigmatic lives. The documented geographic distribution of placozoans lies mostly in the nearshore, warm, marine waters of the tropics and subtropics. Although placozoans have long been viewed as benthic organisms, they can be more readily collected from the water column, well above the sea bottom. The full life-history of placozoans is unknown, including the nature of this abundant pelagic phase and all details of sexual reproduction and development. We note observations on the biota associated with placozoans in field collections, in particular the other regular members of the microcommunity in which placozoans occur on our collecting plates and on some factors influencing this assemblage. Among the animals found are some potential predators against which placozoans appear to be defended, although the mechanisms are still to be examined. Also yet to be uncovered is the full breadth of diversity in this phylum, certainly underrepresented by its single named species. We report here greatly expanded distributions for known haplotypes and fresh specimens that include a new haplotype, and we review the evidence that many more almost certainly await discovery. We also describe some methods for collecting and handling these small, fragile animals.
for assistance in obtaining samples. Deutsche Forschungsgemeinschaft (Schi277/10) and the Human Frontier Science Program (HFSP RGP0221/2001-M) are gratefully acknowledged. AGC thanks NSF Grant EAR-9814845 for support of this project at an early stage.
Autophagy is a tightly controlled degradation process involved in various developmental aspects of eukaryotes. However, its involvement in developmental processes of multicellular filamentous ascomycetes is largely unknown. Here, we analyzed the impact of the autophagic proteins SmATG8 and SmATG4 on the sexual and vegetative development of the filamentous ascomycete Sordaria macrospora. A Saccharomyces cerevisiae complementation assay demonstrated that the S. macrospora Smatg8 and Smatg4 genes can functionally replace the yeast homologs. By generating homokaryotic deletion mutants, we showed that the S. macrospora SmATG8 and SmATG4 orthologs were associated with autophagy-dependent processes. Smatg8 and Smatg4 deletions abolished fruiting-body formation and impaired vegetative growth and ascospore germination, but not hyphal fusion. We demonstrated that SmATG4 was capable of processing the SmATG8 precursor. SmATG8 was localized to autophagosomes, whereas SmATG4 was distributed throughout the cytoplasm of S. macrospora. Furthermore, we could show that Smatg8 and Smatg4 are not only required for nonselective macroautophagy, but for selective macropexophagy as well. Taken together, our results suggest that in S. macrospora, autophagy seems to be an essential and constitutively active process to sustain high energy levels for filamentous growth and multicellular development even under nonstarvation conditions.
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