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      Comparative Analysis and Expression of Neuroserpin in Xenopus laevis

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          Serine protease inhibitors form a diverse family of proteins of which most members inhibit target serine proteases. Neuroserpin is a member of this family. Here, we have characterized neuroserpin in the nonmammalian species Xenopus laevis and found a high degree of aminoacid sequence conservation, especially of the reactive center loop, of the Xenopus protein compared to mammalian and chicken neuroserpin sequences, suggesting a conserved target specificity. Neuroserpin mRNA and protein were expressed throughout Xenopus development, while in the adult frog high mRNA expression was found in neuronal and neuroendocrine tissues, and the reproductive organs, and the neuroserpin protein was detected mainly in brain and pituitary. More specifically, in Xenopus pituitary neuroserpin mRNA was expressed higher in the neurointermediate lobe than in the pars distalis. At the protein level, we detected a 55-kDa neuroserpin protein in the pars nervosa, two neuroserpin proteins of 44- and 50-kDa in the melanotrope cells of the pars intermedia, and a 46-kDa product in the pars distalis. On the basis of its relatively high degree of sequence conservation and its expression pattern, we conclude that Xenopus neuroserpin may play an important physiological role, e.g. as a serine protease inhibitor during development, and for proper neuronal and neuroendocrine cell functioning.

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          Most cited references 22

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          Expression of achaete-scute homolog 3 in Xenopus embryos converts ectodermal cells to a neural fate.

          In Drosophila, the proneural genes of the achaete-scute complex encode transcriptional activators that can commit cells to a neural fate. We have isolated cDNAs for two Xenopus achaete-scute homologs, ASH3a and ASH3b, which are expressed in a subset of central nervous system (CNS) neuroblasts during early neurogenesis. After expressing either ASH3 protein in developing Xenopus embryos, we find enlargement of the CNS at the expense of adjacent non-neural ectoderm. Analysis of molecular markers for neural, epidermal, and neural crest cells indicates that CNS expansion occurs as early as neural plate formation. ASH3-dependent CNS enlargement appears to require neural induction, as it does not occur in animal cap explants. Inhibition of DNA synthesis shows that additional CNS tissue does not depend on cell division--rather it reflects conversion of prospective neural crest and epidermal cells to a neural fate. The differentiation of the early forming primary neurons also seems to be prevented by ASH3 expression. This may be secondary to the observed activation of Xotch transcription by ASH3.
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            Albumin phylogeny for clawed frogs (Xenopus).

            Comparisons of albumin indicate that the frogs commonly used by North American molecular and developmental biologists under the name of Xenopus muelleri belong to another species, X. borealis. Phylogenetic analysis of the albumin data reveals two major groups of Xenopus species, one containing only X. tropicalis and the other, called the X. laevis grou, containing the remaining species of the genus. The phylogenetic tree, in conjunction with evidence from chromosomes and DNA content, leads to the hypothesis that total genome duplication occurred in the common ancestor of the X. laevis group.
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              The axonally secreted serine proteinase inhibitor, neuroserpin, inhibits plasminogen activators and plasmin but not thrombin.

              Neuroserpin is an axonally secreted serine proteinase inhibitor that is expressed in neurons during embryogenesis and in the adult nervous system. To identify target proteinases, we used a eucaryotic expression system based on the mouse myeloma cell line J558L and vectors including a promoter from an Ig-kappa-variable region, an Ig-kappa enhancer, and the exon encoding the Ig-kappa constant region (C kappa) and produced recombinant neuroserpin as a wild-type protein or as a fusion protein with C kappa. We investigated the capability of recombinant neuroserpin to form SDS-stable complexes with, and to reduce the amidolytic activity of, a variety of serine proteinases in vitro. Consistent with its primary structure at the reactive site, neuroserpin exhibited inhibitory activity against trypsin-like proteinases. Although neuroserpin bound and inactivated plasminogen activators and plasmin, no interaction was observed with thrombin. A reactive site mutant of neuroserpin neither formed complexes with nor inhibited the amidolytic activity of any of the tested proteinases. Kinetic analysis of the inhibitory activity revealed neuroserpin to be a slow binding inhibitor of plasminogen activators and plasmin. Thus, we postulate that neuroserpin could represent a regulatory element of extracellular proteolytic events in the nervous system mediated by plasminogen activators or plasmin.

                Author and article information

                S. Karger AG
                January 2006
                27 January 2006
                : 82
                : 1
                : 11-20
                Department of Molecular Animal Physiology, Institute for Neuroscience, Nijmegen Center for Molecular Life Sciences (NCMLS), Radboud University, Nijmegen, The Netherlands
                90011 Neuroendocrinology 2005;82:11–20
                © 2005 S. Karger AG, Basel

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                Page count
                Figures: 5, References: 33, Pages: 10
                Original Paper


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