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Christopher J Lowe

Publications and source records attributed to Christopher J Lowe.

8 recordsLinked to original sources
PubMed2006

Deuterostome phylogeny reveals monophyletic chordates and the new phylum Xenoturbellida.

Deuterostomes comprise vertebrates, the related invertebrate chordates (tunicates and cephalochordates) and three other invertebrate taxa: hemichordates, echinoderms and Xenoturbella. The relationships between invertebrate and vertebrate deuterostomes are clearly important for understanding our own distant origins. Recent phylogenetic studies of chordate classes and a sea urchin have indicated that urochordates might be the closest invertebrate sister group of vertebrates, rather than cephalochordates, as traditionally believed. More remarkable is the suggestion that cephalochordates are closer to echinoderms than to vertebrates and urochordates, meaning that chordates are paraphyletic. To study the relationships among all deuterostome groups, we have assembled an alignment of more than 35,000 homologous amino acids, including new data from a hemichordate, starfish and Xenoturbella. We have also sequenced the mitochondrial genome of Xenoturbella. We support the clades Olfactores (urochordates and vertebrates) and Ambulacraria (hemichordates and echinoderms). Analyses using our new data, however, do not support a cephalochordate and echinoderm grouping and we conclude that chordates are monophyletic. Finally, nuclear and mitochondrial data place Xenoturbella as the sister group of the two ambulacrarian phyla. As such, Xenoturbella is shown to be an independent phylum, Xenoturbellida, bringing the number of living deuterostome phyla to four.

Animals↗
PubMed2006

Determination of acidic drugs and caffeine in municipal wastewaters and receiving waters by gas chromatography-ion trap tandem mass spectrometry.

Some aspects of both sample preparation and instrumental techniques for analysis of such acidic drugs as acetylsalicylic acid, ibuprofen, gemfibrozil, fenoprofen, naproxen, ketoprofen, and diclofenac, as well as caffeine in surface water and municipal wastewater have been studied and further developed. Water samples were filtered and target analytes were extracted by solid-phase extraction (SPE). Supelco LC-18 and Oasis HLB SPE cartridges were used to pre-concentrate samples for acidic drugs and caffeine, respectively. A methylation process was applied to acidic drugs prior to analysis while caffeine was analyzed directly. A method of gas chromatography-ion trap tandem mass spectrometry (IT-MS/MS) for analysis of the target acidic pharmaceuticals and caffeine is presented here in detail. Such parameters as collision-induced dissociation (CID) voltage, isolation time, excitation time, excitation storage level, and electron energy were adjusted in order to optimize the instrument analytical performance. After optimization, an instrument detection limit of 0.5-20 pg/microL with signal-to-noise (S/N) not less than 5 was achieved for all target analytes. It was shown that this method has good linearity within the range of 10-2000 pg/microL. The application of the optimized IT-MS/MS parameters conjointly with the sample preparation procedure resulted in method detection limits (MDLs) of 0.1-1.0 and 20 ng/L for the determination of acidic drugs and caffeine, respectively in such samples as surface water, effluent from municipal wastewater plants, as well as receiving waters.

Acids↗
PubMed2006

Dorsoventral patterning in hemichordates: insights into early chordate evolution.

We have compared the dorsoventral development of hemichordates and chordates to deduce the organization of their common ancestor, and hence to identify the evolutionary modifications of the chordate body axis after the lineages split. In the hemichordate embryo, genes encoding bone morphogenetic proteins (Bmp) 2/4 and 5/8, as well as several genes for modulators of Bmp activity, are expressed in a thin stripe of ectoderm on one midline, historically called "dorsal." On the opposite midline, the genes encoding Chordin and Anti-dorsalizing morphogenetic protein (Admp) are expressed. Thus, we find a Bmp-Chordin developmental axis preceding and underlying the anatomical dorsoventral axis of hemichordates, adding to the evidence from Drosophila and chordates that this axis may be at least as ancient as the first bilateral animals. Numerous genes encoding transcription factors and signaling ligands are expressed in the three germ layers of hemichordate embryos in distinct dorsoventral domains, such as pox neuro, pituitary homeobox, distalless, and tbx2/3 on the Bmp side and netrin, mnx, mox, and single-minded on the Chordin-Admp side. When we expose the embryo to excess Bmp protein, or when we deplete endogenous Bmp by small interfering RNA injections, these expression domains expand or contract, reflecting their activation or repression by Bmp, and the embryos develop as dorsalized or ventralized limit forms. Dorsoventral patterning is independent of anterior/posterior patterning, as in Drosophila but not chordates. Unlike both chordates and Drosophila, neural gene expression in hemichordates is not repressed by high Bmp levels, consistent with their development of a diffuse rather than centralized nervous system. We suggest that the common ancestor of hemichordates and chordates did not use its Bmp-Chordin axis to segregate epidermal and neural ectoderm but to pattern many other dorsoventral aspects of the germ layers, including neural cell fates within a diffuse nervous system. Accordingly, centralization was added in the chordate line by neural-epidermal segregation, mediated by the pre-existing Bmp-Chordin axis. Finally, since hemichordates develop the mouth on the non-Bmp side, like arthropods but opposite to chordates, the mouth and Bmp-Chordin axis may have rearranged in the chordate line, one relative to the other.

Animals↗
PubMed2003

Anteroposterior patterning in hemichordates and the origins of the chordate nervous system.

The chordate central nervous system has been hypothesized to originate from either a dorsal centralized, or a ventral centralized, or a noncentralized nervous system of a deuterostome ancestor. In an effort to resolve these issues, we examined the hemichordate Saccoglossus kowalevskii and studied the expression of orthologs of genes that are involved in patterning the chordate central nervous system. All 22 orthologs studied are expressed in the ectoderm in an anteroposterior arrangement nearly identical to that found in chordates. Domain topography is conserved between hemichordates and chordates despite the fact that hemichordates have a diffuse nerve net, whereas chordates have a centralized system. We propose that the deuterostome ancestor may have had a diffuse nervous system, which was later centralized during the evolution of the chordate lineage.

Animals↗
PubMedDate not supplied

Gene expression and larval evolution: changing roles of distal-less and orthodenticle in echinoderm larvae.

We describe the expression of the homeobox genes orthodenticle (Otx) and distal-less (Dlx) during the larval development of seven species representing three classes of echinoderms: Holothuroidea, Asteroidea, and Echinoidea. Several expression domains are conserved between species within a single class, including Dlx expression within the brachiolar arms of asteroid larvae and Otx expression within the ciliated bands of holothuroid larvae. Some expression domains are apparently conserved between classes, such as the expression of Dlx within the hydrocoel (left mesocoel) in all three classes. However, several substantial differences in expression domains among taxa were also evident for both genes. Some autapomorphic (unique derived) features of gene expression are phylogenetically associated with autapomorphic structures, such as Dlx expression within the invaginating rudiment of euechinoids. Other autapomorphic gene expression domains are associated with evolutionary shifts in life history from feeding to nonfeeding larval development, such as Otx expression within the ciliated bands of a nonfeeding holothuroid larva. Similar associations between evolutionary changes in morphology and life history mode with changes in regulatory gene expression have also been observed in arthropods, urochordates, and chordates. We predict that recruitment of regulatory genes to a new developmental role is commonly associated with evolutionary changes in morphology and may be particularly common in clades with complex life cycles and diversity of life history modes. Caution should be used when making generalizations about gene expression and function based on a single species, which may not accurately reflect developmental processes and life histories of the phyla to which it belongs.

Animals↗