Although the presence of chitin in nematodes is well documented little is known about its synthesis in this phyletic group. The recently completed genome sequence of Caenorhabditis elegans predicts two sequences with homology to chitin synthases (chitin-UDP acetyl-glucosaminyl transferase; EC 2.4.1.16). We show that these genes are differentially expressed in a pattern that may reflect different functional roles. One gene is expressed predominantly in the adult hermaphrodite (the main egg-producing stage in the nematode) and later larval stages, which is consistent with a role in production of chitin for the eggshell. The other gene, however, is expressed in the cells that form the pharynx, and only in the period directly preceding a moult. These data suggest that the product of this gene is involved in synthesis of the feeding apparatus, which is replaced during each moult. We have also isolated a full-length genomic sequence of a chitin synthase orthologue from the plant parasitic nematode Meloidogyne artiellia. The single gene present in M. artiellia shows an expression pattern that is consistent with a role for the protein in production of the eggshell.
A study has been made of the accuracy of clinical assessment, the fluorescein test, and phlebography in the localization of incompetent perforating veins using an extensive subfascial exploration as the method of assessing the results. Clinical assessment was found to be 48 per cent accurate, the fluorescein test 39 per cent accurate, and phlebography 69 per cent accurate. Although phlebography is the most useful investigation we do not feel that it can be used to restrict a full surgical exploration of the medial side of the leg. However, it is valuable in drawing attention to the presence of incompetent perforating veins on the lateral aspect of the legs which in this series occurred in I of every 2 patients.
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