Hepatocyte growth factor/scatter factor is a motogen for interneurons migrating from the ventral to dorsal telencephalon

Cortical interneurons arise from the proliferative zone of the ventral telencephalon, the ganglionic eminence, and migrate into the developing neocortex. The spatial patterns of migratory interneurons reflect the complementary expression of hepatocyte growth factor/scatter factor (HGF/SF) and its receptor, MET, in the forebrain. Scatter assays on forebrain explants demonstrate regionally specific motogenic activity due to HGF/SF. In addition, exogenous ligand disrupts normal cell migration. Mice lacking the urokinase-type plasminogen activator receptor (u-PAR), a key component of HGF/SF activation, exhibit deficient scatter activity in the forebrain, abnormal interneuron migration from the ganglionic eminence, and reduced interneurons in the frontal and parietal cortex. The data suggest that HGF/SF motogenic activity, which is essential for normal development of other organ systems, is a conserved mechanism that regulates trans-telencephalic migration of interneurons.     

Adenosine and dopamine receptor antagonist binding in the rat ventral and dorsal striatum: lack of changes after a neonatal bilateral lesion of the ventral hippocampus.

There is experimental evidence from radioligand binding experiments for the existence of strong antagonistic interactions between different subtypes of adenosine and dopamine receptors in the striatum, mainly between adenosine A1 and dopamine D1 and between adenosine A2A and dopamine D2 receptors. These interactions seem to be more powerful in the ventral compared to the dorsal striatum, which might have some implications for the treatment of schizophrenia. The binding characteristics of different dopamine and adenosine receptor subtypes were analysed in the different striatal compartments (dorsolateral striatum and shell and core of the nucleus accumbens), by performing saturation experiments with the dopamine D1 receptor antagonist [125I]SCH-23982, the dopamine D2-3 receptor antagonist [3H]raclopride, the adenosine A1 receptor antagonist [3H]DPCPX and the adenosine A2A receptor antagonist [3H]SCH 58261. The experiments were also performed in rats with a neonatal bilateral lesion of the ventral hippocampus (VH), a possible animal model of schizophrenia. Both dopamine D2-3 and adenosine A2A receptors follow a similar pattern, with a lower density of receptors (40%) in the shell of the nucleus accumbens compared with the dorsolateral caudate-putamen. A lower density of adenosine A1 receptors (20%) was also found in the shell of the nucleus accumbens compared with the caudate-putamen. On the other hand, dopamine D1 receptors showed a similar density in the different striatal compartments. Therefore, differences in receptor densities cannot explain the stronger interactions between adenosine and dopamine receptors found in the ventral, compared to the dorsal striatum. No statistical differences in the binding characteristics of any of the different adenosine and dopamine receptor antagonists used were found between sham-operated and VH-lesioned rats.     

Lack of the murine homeobox gene Hesx1 leads to a posterior transformation of the anterior forebrain

The homeobox gene Hesx1 is an essential repressor that is required within the anterior neural plate for normal forebrain development in mouse and humans. Combining genetic cell labelling and marker analyses, we demonstrate that the absence of Hesx1 leads to a posterior transformation of the anterior forebrain (AFB) during mouse development. Our data suggest that the mechanism underlying this transformation is the ectopic activation of Wnt/beta-catenin signalling within the Hesx1 expression domain in the AFB. When ectopically expressed in the developing mouse embryo, Hesx1 alone cannot alter the normal fate of posterior neural tissue. However, conditional expression of Hesx1 within the AFB can rescue the forebrain defects observed in the Hesx1 mutants. The results presented here provide new insights into the function of Hesx1 in forebrain formation.     

Immunohistochemical evidence for a mesothelial contribution to the ventral wall of the avian aorta

We report morphological and immunohistochemical evidence for a translocation of cells from the coelomic mesothelium to the aortic wall between the developmental stages HH16 and HH22 of the quail embryos. The coelomic mesothelial cells closest to the aorta showed, at these stages, increased mitotic activity, reduced intercellular adhesion, loss of tight junctions, and long basal cytoplasmic processes. Coinciding with these morphological traits, cytokeratin immunoreactivity was found in the mesothelium, in cells of the aortic wall and throughout the ventral periaortic mesenchyme (but not in the lateral and dorsal aortic regions). Vimentin immunoreactivity colocalized with cytokeratin in the mesothelial cells adjacent to the aorta. In the ventral aortic wall, cytokeratin colocalized with smooth muscle -actin and with the 1E12 antigen (a smooth muscle-specific -actinin isoform). We think that the morphological and immunolocalization data observed are compatible with an epithelial–mesenchymal transition by which mesothelial-derived cells contribute to the splanchnic mesoderm and aortic wall. The precise coincidence between the mesothelial contribution and the emergence of the aortic smooth muscle cells progenitors, as well as the immunolocalization data, suggest a potential relationship of the mesothelial-derived cells with this cell lineage. This may explain the observed ventrodorsal asymmetry in the distribution of smooth muscle cells progenitors in the aortic wall.     

white+ transgene insertions presenting a dorsal/ventral pattern define a single cluster of homeobox genes that is silenced by the polycomb-group proteins in Drosophila melanogaster.

We used the white gene as an enhancer trap and reporter of chromatin structure. We collected white+ transgene insertions presenting a peculiar pigmentation pattern in the eye: white expression is restricted to the dorsal half of the eye, with a clear-cut dorsal/ventral (D/V) border. This D/V pattern is stable and heritable, indicating that phenotypic expression of the white reporter reflects positional information in the developing eye. Localization of these transgenes led us to identify a unique genomic region encompassing 140 kb in 69D1-3 subject to this D/V effect. This region contains at least three closely related homeobox-containing genes that are constituents of the iroquois complex (IRO-C). IRO-C genes are coordinately regulated and implicated in similar developmental processes. Expression of these genes in the eye is regulated by the products of the Polycomb-group (Pc-G) and trithorax-group (trx-G) genes but is not modified by classical modifiers of position-effect variegation. Our results, together with the report of a Pc-G binding site in 69D, suggest that we have identified a novel cluster of target genes for the Pc-G and trx-G products. We thus propose that ventral silencing of the whole IRO-C in the eye occurs at the level of chromatin structure in a manner similar to that of the homeotic gene complexes, perhaps by local compaction of the region into a heterochromatin-like structure involving the Pc-G products.     

Three mitochondrial tRNA genes from Arabidopsis thaliana: evidence for the conversion of a tRNAPhe gene into a tRNATyr gene.

Three tRNA genes have been isolated from a genomic library of Arabidopsis thaliana: a tRNASer (GCU), a tRNATyr (GUA) and a tRNAGlu (UUC) genes. These genes are located closely on the same DNA fragment. The tRNASer and the tRNAGlu genes have both 99% sequence similarity with their mitochondrial counterparts from higher plants indicating that these three tRNA genes are mitochondrial. The tRNATyr gene shows a particular high sequence similarity with the mitochondrial tRNAPhe pseudogene from maize, and both genes are flanked by a tRNASer gene in the upstream region. Extensive sequence comparisons of the Arabidopsis thaliana mitochondrial sequence containing the three tRNA genes and the corresponding region from maize and soybean mitochondria have shown evidence that the tRNA Tyr gene has been generated from a mitochondrial tRNAPhe gene. The conversion was accomplished by three genetic events: a 4 base-pair deletion, a mutation and a recombination, which led to the transformation of the acceptor stem and the anticodon.     

Futile attempts to differentiate provide molecular evidence for individual differences within a population of cells during cellular reprogramming

A cryptic plasmid from Arthrobacter rhombi PRH1, designated as pPRH, was sequenced and characterized. It was 5000 bp in length with a G+C content of 66 mol%. The plasmid pPRH was predicted to encode six putative open reading frames (ORFs), in which ORF2 and ORF3 formed the minimal replicon of plasmid pPRH and shared 55-61% and 60-69% homology, respectively, with the RepA and RepB proteins of reported rhodococcal plasmids. Sequence analysis revealed a typical ColE2-type ori located 45 bp upstream of the gene repA. Sequence and phylogenetic analysis led to the conclusion that pPRH is a representative of a novel group of pAL5000 subfamily of ColE2 family plasmids. Three shuttle vectors pRMU824, pRMU824Km and pRMU824Tc, encoding chloramphenicol resistance, were constructed. The latter two harboured additional antibiotic resistance genes kan and tet, respectively. All vectors successfully replicated in Escherichia coli, Arthrobacter and Rhodococcus spp. The vector pRMU824Km was employed for functional screening of 2-hydroxypyridine catabolism encoding genes from Arthrobacter sp. PY22. Sequence analysis of the cloned 6-kb DNA fragment revealed eight putative ORFs, among which hpyB gene encoded a putative monooxygenase.     

Unusual compact rDNA gene arrangements within some members of the Ascomycota: evidence for molecular co-evolution between ITS1 and ITS2.

The internal transcribed spacers of the ribosomal DNA tandem repeat were examined in members of the ascomycetous genus Sphaeronaemella. Species of Sphaeronaemella and its mitotic counterpart Gabarnaudia, have a compact rDNA gene arrangement due to unusually short internal transcribed spacer (ITS) regions. Examination of these regions from phylogenetically related taxa, Cornuvesica, Gondwanamyces, and Ceratocystis, showed that their ITS1 and ITS2 regions could be folded into central hairpin-like structures with the size reduction in species of Sphaeronaemella being due to length reduction of the main-hairpin and the loss of smaller hairpin-like structures that emanate from the main hairpin. A databank compilation, combined with newly obtained sequences, provided an ITS data set that includes sequences of 600 species belonging to the Ascomycota. Correlation analysis revealed that the sizes of ITS1 and ITS2 show a strong positive correlation, suggesting that the 2 rDNA regions have co-evolved. This supports biochemical evidence indicating that the ITS1 and ITS2 segments interact to facilitate the maturation of the rRNA precursor.     

Neural expression of the Xenopus homeobox gene Xhox3: evidence for a patterning neural signal that spreads through the ectoderm

The Xenopus laevis homeobox gene Xhox3 is expressed in the axial mesoderm of gastrula and neurula stage embryos. By the late neurula-early tailbud stage, mesodermal expression is no longer detectable and expression appears in the growing tailbud and in neural tissue. In situ hybridization analysis of the expression of Xhox3 in neural tissue shows that it is restricted within the neural tube and the cranial neural crest during the tailbud-early tadpole stages. In late tadpole stages, Xhox3 is only expressed in the mid/hindbrain area and can therefore be considered a marker of anterior neural development. To investigate the mechanism responsible for the anterior-posterior (A-P) regionalization of the neural tissue, the expression of Xhox3 has been analysed in total exogastrula. In situ hybridization analyses of exogastrulated embryos show that Xhox3 is expressed in the apical ectoderm of total exogastrulae, a region that develops in the absence of anterior axial mesoderm. The results provide further support for the existence of a neuralizing signal, which originates from the organizer region and spreads through the ectoderm. Moreover, the data suggest that this neural signal also has a role in A-P patterning the neural ectoderm.     

The molecular function of Ase1p: evidence for a MAP-dependent midzone-specific spindle matrix. Microtubule-associated proteins

The midzone is the domain of the mitotic spindle that maintains spindle bipolarity during anaphase and generates forces required for spindle elongation (anaphase B). Although there is a clear role for microtubule (MT) motor proteins at the spindle midzone, less is known about how microtubule-associated proteins (MAPs) contribute to midzone organization and function. Here, we report that budding yeast Ase1p is a member of a conserved family of midzone-specific MAPs. By size exclusion chromatography and velocity sedimentation, both Ase1p in extracts and purified Ase1p behaved as a homodimer. Ase1p bound and bundled MTs in vitro. By live cell microscopy, loss of Ase1p resulted in a specific defect: premature spindle disassembly in mid-anaphase. Furthermore, when overexpressed, Ase1p was sufficient to trigger spindle elongation in S phase-arrested cells. FRAP revealed that Ase1p has both a very slow rate of turnover within the midzone and limited lateral diffusion along spindle MTs. We propose that Ase1p functions as an MT cross-bridge that imparts matrix-like characteristics to the midzone. MT-dependent networks of spindle midzone MAPs may be one molecular basis for the postulated spindle matrix.     

Microinjection of DLH into the region of the caudal ventral respiratory column in the cat: evidence for an endogenous cough-suppressant mechanism.

The caudal ventral respiratory column (cVRC) contains premotor expiratory neurons that play an important role in cough-related expiratory activity of chest wall and abdominal muscles. Microinjection of d,l-homocysteic acid (DLH) was used to test the hypothesis that local activation of cVRC neurons can suppress the cough reflex. DLH (20-50 mM, 10-30 nl) was injected into the region of cVRC in nine anesthetized spontaneously breathing cats. Repetitive coughing was elicited by mechanical stimulation of the intrathoracic airways. Electromyograms (EMG) were recorded bilaterally from inspiratory parasternal and expiratory transversus abdominis (ABD) and unilaterally from laryngeal posterior cricoarytenoid and thyroarytenoid muscles. Unilateral microinjection of DLH (1-1.5 nmol) elicited bilateral increases in tonic and phasic respiratory ABD EMG activity, and it altered the respiratory pattern and laryngeal motor activities. However, DLH also decreased cough frequency by 51 +/- 7% compared with control (P < 0.001) and the amplitude of the contralateral (-35 +/- 3%; P < 0.001) and ipsilateral (-34 +/- 5%; P < 0.001) ABD EMGs during postinjection coughs compared with control. The cough alterations were much less pronounced after microinjection of a lower dose of DLH (0.34-0.8 nmol). No cough depression was observed after microinjections of vehicle. These results suggest that an endogenous cough suppressant neuronal network in the region of the cVRC may exist, and this network may be involved in the control of cough reflex excitability.     

Unequal crossing-over within the B duplication of Drosophila melanogaster: a molecular analysis.

The B mutation is associated with a tandem duplication of 16A1-16A7. It is unstable, mutating to wild type and to a more extreme form at a frequency of one in 1000 to 3000. The reversion to wild type is associated with the loss of one copy of the duplication, whereas the mutation to extreme B is associated with a triplication of the region. The instability of B has been attributed to unequal crossing-over between the two copies of the duplication. Recent molecular data show that there is a transposable element, B104, between the two copies of the duplication and support the hypothesis that this element generated the duplication via a recombination event. These data suggest that unequal crossing-over within the duplication may not be the cause of the instability of B. Instead, the instability may be caused by a recombination event involving the B104 element. This issue was addressed using probes for the DNA on either side of the B104 element at the B breakpoint. All of the data indicate that the B104 element is not involved in the instability of B and support the original unequal crossing-over model.     

Transduction of c-myb into avian myeloblastosis virus: locating points of recombination within the cellular gene.

The oncogene (v-myb) of avian myeloblastosis virus apparently arose by transduction of nucleotide sequences from a cellular gene (c-myb). In c-myb the nucleotide sequences that formed v-myb exist at seven distinct regions separated by nontransduced stretches of sequence that are flanked by eucaryotic splice signals. By contrast, the sequences at the outside boundaries of the transduced region of c-myb do not resemble splice sites. We mapped the nucleotide sequences that are homologous to the ends of v-myb with respect to the exons and introns of c-myb. The results indicate that the leftward recombination between c-myb and the transducing retrovirus occurred within an intron of the cellular gene, whereas the rightward recombination took place in an exon of c-myb. Transduction of c-myb sequences may therefore have involved a DNA rearrangement.     

Analysis of the distribution and molecular heterogeneity of the ospD gene among the Lyme disease spirochetes: evidence for lateral gene exchange.

Analysis of the ospD gene has revealed that this gene is not universal among Lyme disease spirochete isolates. The gene was found to be carried by 90, 50, and 24% of the Borrelia garinii, B. afzelii, and B. burgdorferi isolates tested. Size variability in the ospD-encoding plasmid was also observed. Sequence analysis has demonstrated the presence of various numbers of a 17-bp repeated sequence in the upstream control (promoter) region of the gene. In addition, a region within the coding sequence where various insertions, deletions, and direct repeats occur was identified. ospD gene sequences from 31 different isolates were determined and utilized in pairwise sequence comparisons and construction of a gene tree. These analyses suggest that the ospD gene was the target of several recombinational events and that the gene was recently acquired by Lyme disease spirochetes and laterally transferred between species.