Molecular patterning of the oikoplastic epithelium of the larvacean tunicate Oikopleura dioica.

Appendicularia are protochordates that rely on a complex mucous secretion, the house, to filter food particles from seawater. A monolayer of cells covering the trunk of the animal, the oikoplastic epithelium, secretes the house. This epithelium contains a fixed number of cells arranged in characteristic patterns with distinct sizes and nuclear morphologies. Certain house structures appear to be spatially related to defined, underlying groups of cells in the epithelium. We show that the house is composed of at least 20 polypeptides, a number of which are highly glycosylated, with glycosidase treatments resulting in molecular mass shifts exceeding 100 kDa. Nanoelectrospray tandem mass spectrometric microsequencing of house polypeptides was used to design oligonucleotides to screen an adult Oikopleura dioica cDNA library. This resulted in the isolation of cDNAs coding for three different proteins, oikosin 1, oikosin 2, and oikosin 3. The latter two are novel proteins unrelated to any known data base entries. Oikosin 1 has 13 repeats of a Cys domain, previously identified as a subunit of repeating sequences in some vertebrate mucins. We also find one repeat of this Cys domain in human cartilage intermediate layer protein but find no evidence of this domain in any invertebrate species, including those for which entire genomes have been sequenced. The three oikosins show distinct and complementary expression patterns restricted to the oikoplastic epithelium. This easily accessible epithelium, with differential gene expression patterns in readily identifiable groups of cells with distinctive nuclear morphologies, is a highly attractive model system for molecular studies of pattern formation.

Diverse genes expressed in distinct regions of the trunk epithelium define a monolayer cellular template for construction of the oikopleurid house.

The filter-feeding house secreted by urochordate Appendicularians is among the most complex extracellular structures constructed by any organism. This structure allows the Appendicularia to exploit a wide range of food particle sizes, including nanoplankton and submicrometer colloids, establishing them as an important and abundant component of marine zooplankton communities throughout the world. The oikoplastic epithelium, a monolayer of cells covering the trunk of the animal, is responsible for secretion of the house. The epithelium has a fixed number of cells, organized in distinct fields, characterized by defined cell shapes and nuclear morphologies. Certain structures in the house appear to be spatially linked to these different fields of cells. Using cDNA representation difference analysis (cDNA RDA) on whole animals at two different developmental stages separated by the metamorphic tailshift event, we isolated four families of genes (oikosins) that are expressed only from specific subregions of the oikoplastic epithelium. The molecular patterns defined by oikosin gene expression establish the epithelium as an ideal and easily accessible monolayer cellular template for exploring coordinate regulation of gene expression, cell-cell interactions involved in pattern formation, gene/genome amplification, and the role of temporal changes in nuclear architecture in regulating gene expression.

Complete DNA sequence of yeast chromosome II.

In the framework of the EU genome-sequencing programmes, the complete DNA sequence of the yeast Saccharomyces cerevisiae chromosome II (807 188 bp) has been determined. At present, this is the largest eukaryotic chromosome entirely sequenced. A total of 410 open reading frames (ORFs) were identified, covering 72% of the sequence. Similarity searches revealed that 124 ORFs (30%) correspond to genes of known function, 51 ORFs (12.5%) appear to be homologues of genes whose functions are known, 52 others (12.5%) have homologues the functions of which are not well defined and another 33 of the novel putative genes (8%) exhibit a degree of similarity which is insufficient to confidently assign function. Of the genes on chromosome II, 37-45% are thus of unpredicted function. Among the novel putative genes, we found several that are related to genes that perform differentiated functions in multicellular organisms of are involved in malignancy. In addition to a compact arrangement of potential protein coding sequences, the analysis of this chromosome confirmed general chromosome patterns but also revealed particular novel features of chromosomal organization. Alternating regional variations in average base composition correlate with variations in local gene density along chromosome II, as observed in chromosomes XI and III. We propose that functional ARS elements are preferably located in the AT-rich regions that have a spacing of approximately 110 kb. Similarly, the 13 tRNA genes and the three Ty elements of chromosome II are found in AT-rich regions. In chromosome II, the distribution of coding sequences between the two strands is biased, with a ratio of 1.3:1. An interesting aspect regarding the evolution of the eukaryotic genome is the finding that chromosome II has a high degree of internal genetic redundancy, amounting to 16% of the coding capacity.

The sequence of a 32,420 bp segment located on the right arm of chromosome II from Saccharomyces cerevisiae.

The sequence of a 32,420 bp segment of Saccharomyces cerevisiae chromosome II has been deduced. The sequence data revealed 19 potential new genes covering 83.5% of the sequence. Four genes had already been cloned and sequenced: part of RIF1, DPB3, MRP-L27 and SNF5. Besides these four genes, 15 open reading frames (ORFs) of at least 100 amino acids encoding potential new genes were identified. Two of these ORFs are overlapping and a third is located within another ORF. The putative gene product of ORF YBR2039 was homologous to the group of uncoupling proteins involved in the mitochondrial energy transfer system. We propose a remapping of the MRP-L27 gene encoding the mitoribosomal protein YmL27 as it previously has been mapped on chromosome X. The ORF YBR2020 has a strong homology with a 31.9% identity in a 473 amino acid region to the yeast gene SEC61, suggesting that YBR2020 is a new gene encoding a protein involved in translocation of proteins in the yeast cell. Six of the potential genes do not exhibit any significant homology to previously sequenced genes as predicted in the Fast A analysis.