Length of uninterrupted repeats determines instability at the unstable mouse expanded simple tandem repeat family MMS10 derived from independent SINE B1 elements

Mouse expanded simple tandem repeats (ESTRs) provide highly informative loci for analyzing spontaneous and induced germline mutation. We have conducted an extensive sequence database search and identified 17 new members of the highly unstable rodent-specific ESTR family called MMS10. This family has arisen by independent expansions of a common GGCAGA repeat unit from within a subset of both ancestral and modern SINE B1 elements during the course of mouse evolution. Analysis of the interspersion patterns of variant repeats along alleles of 20 of these MMS10 loci revealed two distinct classes of tandem arrays: one composed of uninterrupted GGCAGA repeats and the second with generally larger arrays interrupted by variant units. Surveys of allelic diversity at 11 representative members of these two classes of loci in various laboratory strains and BXD recombinant inbred lines revealed that the level of repeat instability was positively correlated with the length of uninterrupted repeats. Turnover processes at MMS10 loci, therefore, appear similar to the type of mechanism observed at human microsatellites. The MMS10 family thus provides a potentially useful murine model for studying dynamic mutation at simple tandem repeats.     

Bulinus tropicus, a natural intermediate host for Schistosoma margrebowiei in Lochinvar National Park, Zambia

Snails, provisionally identified as Bulinus tropicus, on the basis of chromosome number, egg protein profile, AcP and HBDH enzymes of the digestive gland, and radular morphology, from Lochinvar National Park, Zambia have been demonstrated to transmit Schistosoma margrebowiei naturally. The identification of the unpaired male schistosomes was confirmed by PGM and AcP analyses. The observations confirm earlier epidemiological predictions, and add another species of mollusc to the two, B. forskalii and B. scalaris, known to be natural intermediate hosts of S. margrebowiei.     

Aquatic snails of the Jonglei region,southern Sudan,and transmission of trematode parasites

An account is given of the aquatic gastropod molluscs obtained in a survey made to assess future ecological effects of the Jonglei Canal now under construction in the Sudd region of southern Sudan. A total of about 23 species of aquatic snail lives in this region, of which a number are utilised as intermediate hosts by trematode parasites infecting man, livestock and wild herbivores, causing the diseases schistosomiasis, fascioliasis and amphistomiasis. Public health and veterinary authorities should be alert to the possibility that the Jonglei Canal will increase snail populations and raise the prevalence of parasitic diseases.Jonglei Range Ecology Survey.     

The Myofibrillar Protein,Projectin, is Highly Conserved Across Insect Evolution Except for Its PEVK Domain

All striated muscles respond to stretch by a delayed increase in tension. This physiological response, known as stretch activation, is, however, predominantly found in vertebrate cardiac muscle and insect asynchronous flight muscles. Stretch activation relies on an elastic third filament system composed of giant proteins known as titin in vertebrates or kettin and projectin in insects. The projectin insect protein functions jointly as a “scaffold and ruler” system during myofibril assembly and as an elastic protein during stretch activation. An evolutionary analysis of the projectin molecule could potentially provide insight into how distinct protein regions may have evolved in response to different evolutionary constraints. We mined candidate genes in representative insect species from Hemiptera to Diptera, from published and novel genome sequence data, and carried out a detailed molecular and phylogenetic analysis. The general domain organization of projectin is highly conserved, as are the protein sequences of its two repeated regions—the immunoglobulin type C and fibronectin type III domains. The conservation in structure and sequence is consistent with the proposed function of projectin as a scaffold and ruler. In contrast, the amino acid sequences of the elastic PEVK domains are noticeably divergent, although their length and overall unusual amino acid makeup are conserved. These patterns suggest that the PEVK region working as an unstructured domain can still maintain its dynamic, and even its three-dimensional, properties, without the need for strict amino acid conservation. Phylogenetic analysis of the projectin proteins also supports a reclassification of the Hymenoptera in relation to Diptera and Coleoptera. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Does the MRCGP examination discriminate against Asian doctors?

OBJECTIVE--To ascertain whether the membership examination for the Royal College of General Practitioners (MRCGP) discriminates against doctors of Indian subcontinent ethnic origin ("Asian doctors"). DESIGN--Retrospective analysis of data from five administrations of the MRCGP examination (December 1988-December 1990). SETTING--United Kingdom national examination body. SUBJECTS--3686 doctors taking the examination for the first time, 244 of whom were classified as Asian, the remainder as non-Asian. MAIN OUTCOME MEASURES--Comparison of performance in each of the written and oral components of the examination between Asian doctors, identified by their names and classified into subgroups by countries of birth and primary medical training from data provided at registration, and non-Asian doctors. RESULTS--On written components of the examination (multiple choice paper mean score Asians versus non-Asians 42.3 v 48.6, modified essay paper 40.9 v 48.9, practice topic/critical reading paper 41.5 v 48.7, all p less than 0.001 by t testing). But analysis by countries of birth and primary training showed that these differences were due largely to poor performance by certain groups of Asian doctors, especially those born and trained in the Indian subcontinent or elsewhere outside the United Kingdom. Asian doctors born and trained in the United Kingdom and those born in Africa or the West Indies and trained in the United Kingdom performed similarly to the non-Asian doctors. CONCLUSIONS--The examination does not systematically discriminate against Asian doctors, but the poor performance of the two subgroups of Asians is cause for serious concern and requires investigation.     

Observations on the fine structure of the cercaria of Notocotylus attenuatus and formation of the cyst wall of the metacercaria

Summary The dorsal tegument of the mature cercaria of Notocotylus attenuatus is a syncytial, cytoplasmic layer, containing two types of secretory granule which are identifiable ultrastructurally. The type 1 secretory bodies are electron lucid, whereas most type 2 granules have a banded appearance. The ventral tegument contains granules which are secreted from the type 3 cells; the type 3 granules are membrane bound, electron dense, and consist of both an amorphous and a finely striated zone. The type 4 cells mainly contain cigar-shaped granules consisting of an amorphous core surrounded by concentric striations. The granules exhibit structural variability in shape and content. The type 4 cells undergo a cellular migration to the tegument during encystment. The structure of the posterior-lateral glands and mode of secretion of the granules are described. Possible functions of microtubules are discussed for each cell type. Details of some secretory processes involved in the formation of the hemispherical cyst wall are described. The layers of the cyst wall may be related to the granular contents of the various parenchymal cells of the cercaria. The tegument of the metacercaria originates primarily from the cytoplasm of the type 1, type 2, type 3 and type 4 cells.     

Structural data for the carbohydrate of ispaghula husk ex Plantago ovata forsk

The husk from the seeds of Plantago ovata Forsk yielded two fractions when exposed to mild aikali, namely, the mucilage polysaccharide (85%, apparently a single species) and the non-polysaccharide component (15%). Methylation analysis and partial hydrolysis with acid showed the mucilage polysaccharide to be a highly branched, acidic arabinoxylan, the xylan backbone having both (1→4) and (1→3) linkages. The majority of the residues in the xylan backbone are variously substituted at O-2 and O-3 with arabinose, xylose, and an aldobiouronic acid identified as 2-O-(galactopyranosyluronic acid)-rhamnose. A structure incorporating these features for the husk polysaccharide is proposed.