Biomedical subjects
Publications and source records attributed to R H Thomas.
Apparently ancient DNA has been reported from amber-preserved insects many millions of years old. Rigorous attempts to reproduce these DNA sequences from amber- and copal-preserved bees and flies have failed to detect any authentic ancient insect DNA. Lack of reproducibility suggests that DNA does not survive over millions of years even in amber, the most promising of fossil environments.
Complete gene organizations of the mitochondrial genomes of three pulmonate gastropods, Euhadra herklotsi, Cepaea nemoralis and Albinaria coerulea, permit comparisons of their gene organizations. Euhadra and Cepaea are classified in the same superfamily, Helicoidea, yet they show several differences in the order of tRNA and protein coding genes. Albinaria is distantly related to the other two genera but shares the same gene order in one part of its mitochondrial genome with Euhadra and in another part with Cepaea. Despite their small size (14.1-14.5 kbp), these snail mtDNAs encode 13 protein genes, two rRNA genes and at least 22 tRNA genes. These genomes exhibit several unusual or unique features compared to other published metazoan mitochondrial genomes, including those of other molluscs. Several tRNAs predicted from the DNA sequences possess bizarre structures lacking either the T stem or the D stem, similar to the situation seen in nematode mt-tRNAs. The acceptor stems of many tRNAs show a considerable number of mismatched basepairs, indicating that the RNA editing process recently demonstrated in Euhadra is widespread in the pulmonate gastropods. Strong selection acting on mitochondrial genomes of these animals would have resulted in frequent occurrence of the mismatched basepairs in regions of overlapping genes.
Using data from the direct sequencing of fragments of three mitochondrial genes (12S and 16S ribosomal RNA, and cytochrome-b; total length 1469 b.p.) we have reconstructed a gene phylogeny for all 19 living species of the gastropod genus Littorina. Members of the closely related genera Nodilittorina, Littoraria and Mainwaringia have been used as outgroups, and it appears that Littorina is monophyletic. An earlier morphological phylogeny has been revised, and its topology found to be almost entirely consistent with that from the molecular data. The fossil record is sparse, but likewise consistent. A consensus tree is presented, showing clear resolution of basal and terminal branches, and a central unresolved polychotomy. We have used fossil evidence and geological events to estimate the ages of some clades, and thus to calculate average rates of molecular evolution, which in turn provide approximate dates for all branches of the molecular phylogeny. The central polychotomy may be explained by a burst of rapid speciation in the northwestern Pacific during the Middle Miocene, perhaps driven by climatic fluctuation. Our results support the hypothesis that the two clades of Littorina in the northern Atlantic originated from Pacific ancestors which took part in the Pliocene trans-Arctic migration of marine organisms.
The nucleotide sequence of a mitochondrial genome of the pulmonate gastropod mollusc Cepaea nemoralis has been determined. Contained within the 14,100 basepairs (bp) are the two ribosomal RNA genes and 13 protein coding genes typical of metazoan mitochondrial genomes. The Cepaea mtDNA does contain a gene for ATPase subunit 8, like the clausiliid pulmonate, Albinaria, and the chiton, Katharina, but unlike the bivalve mollusc, Mytilus. The mitochondrial genetic code of Cepaea is proposed to be the same as that of Mytilus, Katharina, and Drosophila. Only 14 putative tRNA genes are presented, although there is sufficient unassigned sequence to encode the remainder of the expected total of 22 tRNA genes. These 14 tRNA genes are a mixture of standard cloverleaf structures and nonstandard structures containing TV replacement loops as seen in nematode and mosquito mitochondrial genomes. If the eight unidentified tRNA genes are indeed present, very little unassigned sequence would remain to serve as a control region. Genes are transcribed from both strands of the molecule. Base composition is the least biased for any reported animal mitochondrial genome and is also very little skewed between strands using measures independent of base composition. The Cepaea mitochondrial gene order is quite unlike that of any other reported metazoan mtDNA, with the exception of the recently reported partial sequences of Albinaria. No gene boundaries are shared among all the reported molluscan taxa, demonstrating a complete lack of conservation of mitochondrial gene order across the phylum Mollusca.
A study of 350 women with lichen sclerosus, originally made to elucidate the relationship between lichen sclerosus and autoimmunity, led to the amassing of a considerable amount of clinical material. Our review is confined to those with anogenital lesions (342), supplemented by some new cases (15), giving a total of 357 women with biopsy proven lichen sclerosus. It demonstrates the wide age range of the condition, the association with morphoea and lichen planus and the occurrence of squamous cell carcinoma in some cases. It also shows that inappropriate surgery has continued to be carried out for benign disease.
Genetic data derived from museum collections have an important role in systematics, conservation biology, ecology and medicine. Technical advances in molecular biology are increasing the range of material in collections amenable to such analysis. While the very diversity of natural history collections sometimes makes generalisations difficult, classes of extraction procedures and precautions against contamination can be described. Destructive sampling of specimens for genetic studies raises a number of institutional issues, such as granting of permission to use particular specimens and the return of DNA to the museum housing the specimens. Molecular biology is seen as further enhancing the value of collections.
Grimaldi's recent cladistic classification of genera in the family Drosophilidae, based on adult morphological characters, is evaluated for those taxa for which alcohol dehydrogenase DNA sequences are also available. These data allow us to look at relationships of the Drosophila subgenera Sophophora and Drosophila with the Hawaiian Drosophila (Idiomyia) and with Scaptomyza, when Scaptodrosophila is used as an outgroup. The molecular data give strong support for the broad relationships hypothesized by Throckmorton, who contended that the subgenus Sophophora is a sister group to the remaining ingroup taxa. The Drosophila subgenus Engiscaptomyza, which Throckmorton regarded as intermediate between the Idiomyia (Hawaiian Drosophila) and Scaptomyza, is shown to be much more closely allied with Scaptomyza, in agreement with Grimaldi's results from adult morphology. The Hawaiian taxa, both Idiomyia and Scaptomyza, are firmly located as a sister group to the subgenus Drosophila, and these in turn all form a sister group to the subgenus Sophophora. Grimaldi's classification of these taxa is quite different and places the Hawaiian Drosophila (Idiomyia) as sister group to the remaining ingroup taxa (Scaptomyza and the subgenera Sophophora and Drosophila). Our results show that Grimaldi's new classification of these taxa results in paraphyletic groups, just as does the traditional classification under Throckmorton's interpretation of relationships. Additional data are required to produce a robust classification of this huge paraphyletic genus.
Explore the source record for details and available documents.
The polymerase chain reaction (PCR) was used to amplify small-subunit ribosomal DNA from the anaerobic ciliated protozoon Metopus palaeformis, and from its uncultured endosymbiotic bacteria. This was accomplished directly from total DNA extracted from protozoa without prior isolation or enrichment for symbiont cells. The double-stranded amplification products were precipitated and directly sequenced using the linear PCR reaction. Fluorescent oligonucleotide probes were designed and used in whole-cell hybridizations to provide direct visual evidence that the sequences originated from the host ciliate and from the endosymbiont. Phylogenetic analysis of the Metopus palaeformis sequence consistently placed it as a deep-branching lineage near the root of the ciliate tree. However, the present data were insufficient to resolve the detailed relationship between Blepharisma and Metopus and thus to determine if the heterotrichs are mono- or paraphyletic. Phylogenetic analysis of the symbiont partial sequence clearly demonstrated that it is an archaeobacterium and that it is closely related to, but distinct from, Methanobacterium formicicum.
DNA sequences in the alcohol dehydrogenase genes of flies representing the major groups of Hawaiian Drosophila are used to clarify the relationships of these groups, among themselves and with mainland Drosophila. The topology of the tree derived from these sequences agrees with karyotypic and morphological data but disagrees, in part, with the results of an earlier study that used immunological comparisons between variants of a larval hemolymph protein. A time scale, derived from a comparison of closely related Hawaiian Drosophila species, provides divergence-time estimates that are substantially more recent than those obtained from the immunological studies, although they are still within the bounds set by fossil and biogeographical evidence. The two major lineages of Hawaiian Drosophila, the scaptomyzoids and the drosophiloids, are shown to be widely separated from one another. The scaptomyzoids appear to have diverged early in the history of the subgenus Drosophila, greater than 25 Mya. While hundreds of scaptomyzoid species are found in the Hawaiian archipelago, many fewer are found elsewhere around the world, suggesting that they could have originated outside Hawaii. The drosophiloid lineage is strictly endemic to Hawaii and originated little more than 10 Mya, according to the alcohol dehydrogenase molecular clock. Thus, Drosophila apparently inhabited the Hawaiian archipelago (greater than or equal to 5 Myr before the emergence of the oldest existing high island, Kauai, 5 Mya.
The population structure of several Australian populations of the cactophilic Drosophila buzzatti was investigated, with seasonal samples from two populations analyzed for six polymorphic allozymes. Significant inbreeding throughout the year was detected in both populations, and significant but relatively slight differences in allele frequencies between collections were found in one population. Little significant 2-locus linkage disequilibrium was detected and the variances of linkage disequilibrium coefficients were generally consistent with genetic drift. Individual breeding substrates (rotting cactus cladodes) were collected and the adult flies emerging from them were scored for their allozyme genotypes. The data suggest that approximately ten individuals contribute to the progeny emerging from a rot. The influence of the sizes and distributions of breeding substrates on the maintenance of genetic variation is discussed.
Explore the source record for details and available documents.
A 76-year-old man with bilateral corneal infiltrates secondary to a monoclonal gammopathy of undetermined significance (MGUS) is described. The corneal changes simulated a remote lattice dystrophy. Although the clinical presentation of corneal opacities secondary to paraproteinemic conditions is somewhat variable, this patient's corneas lacked the common crystalline appearance of immunoglobulin deposits. This patient demonstrates an atypical clinical presentation of corneal infiltration secondary to a paraproteinemia.
The phylogenetic affiliation of the extinct marsupial wolf (Thylacinus cynocephalus), which once was widespread in Australia, has been uncertain. On the basis of morphology, some systematists argue that the thylacine was most closely related to an extinct group of South American carnivorous marsupials, the borhyaenids, whereas others consider it to be closer to Australian carnivorous marsupials. Here we use direct sequencing by means of the polymerase chain reaction (PCR) to compare 219 bases of mitochondrial (mt) DNA from museum specimens of the marsupial wolf and representatives of six genera of extant marsupials. In agreement with the results of an antigenic study of albumin, our genetic data suggest that the marsupial wolf was more closely related to other Australian marsupial carnivores than to those of South America. Thus, the marsupial wolf represents an example of convergent morphological evolution to South American carnivorous marsupials as well as to true wolves.
Explore the source record for details and available documents.
Twelve patients with treatment-resistant mosaic plantar warts were treated with aggressive cryotherapy under a general anaesthetic. Seven patients (58%) had complete cure, two patients (16%) experienced substantial but incomplete clearing of their warts and the remaining three patients (25%) had no improvement. The procedure was well tolerated and post cryotherapy pain was acceptable to the patients.
Explore the source record for details and available documents.