Fruiting body formation in ascomycetes is a highly complex process that is under polygenic control and is a fundamental part of the fungal sexual life cycle. However, the molecular determinants regulating this cellular process are largely unknown. Here we show that the sterile pro40 mutant is defective in a 120-kDa WW domain protein that plays a pivotal role in fruiting body maturation of the homothallic ascomycete Sordaria macrospora. Although WW domains occur in many eukaryotic proteins, homologs of PRO40 are present only in filamentous ascomycetes. Complementation analysis with different pro40 mutant strains, using full-sized or truncated versions of the wild-type pro40 gene, revealed that the C terminus of PRO40 is crucial for restoring the fertile phenotype. Using differential centrifugation and protease protection assays, we determined that a PRO40-FLAG fusion protein is located within organelles. Further microscopic investigations of fusion proteins with DsRed or green fluorescent protein polypeptides showed a colocalization of PRO40 with HEX-1, a Woronin body-specific protein. However, the integrity of Woronin bodies is not affected in mutant strains of S. macrospora and Neurospora crassa, as shown by fluorescence microscopy, sedimentation, and immunoblot analyses. We discuss the function of PRO40 in fruiting body formation.Sexual development in filamentous ascomycetes is usually accompanied by the formation of complex fruiting bodies. During this process, a number of specialized cell types have to be generated from a more or less undifferentiated vegetative mycelium (5). This morphogenetic program is a convenient system that allows us to address the following fundamental question: how is multicellular development coordinated in eukaryotes? So far, several environmental and endogenous signals have been described to regulate fruiting body-dependent gene expression in a temporal and spatial manner (for a review, see reference 55). However, even though a decent number of genes involved in this process have been identified, the molecular determinants of fruiting body development have yet to emerge.In this study, we have investigated the homothallic ascomycete Sordaria macrospora, which was recently developed as a model system to study fruiting body morphogenesis (27,36,37,43,52). During early sexual propagation, S. macrospora forms female gametangia, so-called ascogonia, on vegetative hyphae. In subsequent differentiation processes, ascogonia are enveloped by sterile hyphae and develop into spherical premature structures (protoperithecia), which mature into flask-like fruiting bodies (perithecia). In its final developmental stage, each perithecium contains a set of 60 to 80 asci with eight linearly ordered ascospores.Using a forward genetic approach, we aimed to identify numerous developmental genes essential for fruiting body development in S. macrospora. Using conventional mutagenesis, several developmental mutants defective at different stages of perithecium formation were generated (37). In recent years,...

The results of the present (VIIth Complement Genetics Workshop and Conference, Mainz, May 1998) and past reference typing workshops for the terminal complement components C6, C7 and C9 are compiled and discussed both on the protein level and on the DNA level. This report also focusses on the molecular bases of expressed and silent polymorphisms and reviews the molecular bases of subtotal and complete deficiencies of these proteins and their associations with protein and DNA markers. The results of the protein typing for C6 are published in the following paper of this issue.

Intron 9 contains the complete endogenous retrovirus HERV-K(C4) as a 6.4-kb insertion in 60% of human C4 genes. The retroviral insertion is in reverse orientation to the C4 coding sequence. Therefore, expression of C4 could lead to the transcription of an antisense RNA, which might protect against exogenous retroviral infections. To test this hypothesis, open reading frames from the HERV sequence were subcloned in sense orientiation into a vector allowing expression of a beta-galactosidase fusion protein. Mouse L cells which had been stably transfected with either the human C4A or C4B gene both carrying the HERV insertion (LC4 cells), and L(Tk-) cells without the C4 gene were transiently transfected either with a retroviral construct or with the wild-type vector. Expression was monitored using an enzymatic assay. We demonstrated that (1) HERV-K(C4) antisense mRNA transcripts are present in cells constitutively expressing C4, (2) expression of retroviral-like constructs is significantly downregulated in cells expressing C4, and (3) this downregulation is further modulated in a dose-dependent fashion following interferon-gamma stimulation of C4 expression. These results support the hypothesis of a genomic antisense strategy mediated by the HERV-K(C4) insertion as a possible defense mechanism against exogenous retroviral infections.

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