Evidence for the derivation of the Drosophila fushi tarazu gene from a Hox gene orthologous to lophotrochozoan Lox5

The DNA-binding homeobox motif was first identified in several Drosophila homeotic genes but also in fushi tarazu, a gene found in the Hox cluster yet involved in segmentation, not anteroposterior patterning [1]. Homeotic transformations are not seen in insect ftz mutants, and insect ftz genes do not have Hox-like expression except within the nervous system [2] [3]. Insect ftz homeobox sequences link them to the Antp-class genes and Tribolium and Schistocerca orthologs have Antp-class YPWM motifs amino-terminal to the homeobox [2] [3]. Orthologs of ftz cloned from a centipede and an onychophoran [4] show that it predates the emergence of the arthropods, but the inability to pinpoint non-arthropodan orthologs suggested that ftz is the product of a Hox gene duplication in the arthropod ancestor [4] [5]. I have cloned ftz orthologs from a mite and a tardigrade, arthropod outgroups of the insects [6]. Mite ftz is expressed in a Hox-like pattern, confirming its ancestral role in anteroposterior patterning. Phylogenetic analyses indicate that arthropod ftz genes are orthologous to the Lox5 genes of lophotrochozoans (a group that includes molluscs) [7] and, possibly, with the Mab-5 genes of nematodes and Hox6 genes of deuterostomes and would therefore have been present in the triploblast ancestor.     

Golgi-Cox studies on the central nervous system of a gastropod mollusc

Summary Complete neurones were impregnated in the brain of the pulmonate gastropod pond snail, Lymnaea stagnalis L. using the Golgi-Cox method. Mapping of small to medium sized neurones identified in living preparations by the position of the perikarya was possible. Simple monopolar and bifurcating monopolar neurones with varying lateral patterns of short fine fibres were common in the pond snail brain. Larger neurones have more complex and numerous branches originating from axons close to the perikarya than smaller ones. Stem processes originating on the cell body were observed on neurones above 30 in somal diameter. Possible sites for the location of chemical synapses were suggested. Functional types of neurones were difficult to separate on morphological grounds. Giant or very large neurones are small in number in pond snail ganglia, compared with medium or small neurones.The authors wish to thank Mr. Colin Atherton for photographic assistance and the U.K. Science Research Council for a grant to P. R. B.     

Analysis of hunger-driven gene expression in the Drosophila melanogaster larval central nervous system

A transposon-inserted mutant of Drosophila melanogaster was recently identified, and the larvae show no food preference (Ryuda and Hayakawa, 2005). To reveal the genetic mechanism underlying the preference change in this mutant, a large-scale oligo-DNA microarray screening was carried out to identify genes whose expression is different in control and mutant strains. We focused especially on hunger-driven changes in gene expression in the larval central nervous system (CNS) of both strains, because the state of food depletion should promote a feeding response due to changed expression of certain genes in the CNS. We identified 22 genes whose expression changed after starvation in either or both of the two strains. Quantitative RT-PCR analyses confirmed the expression changes in four genes, CG6271, CG6277, CG7953, and new glue 3 (ng3, encoding a putative structural molecule). CG6271 and CG6277 encode triacylglycerol lipase, and CG7953 produces a protein homologous to a juvenile hormone (JH) binding protein. The expression of these two groups of genes was enhanced in control strain larvae with a normal food preference but not in GS1189 strain larvae. Given that these genes contribute to mediating hunger-driven changes in food preference and intake in D. melanogaster larvae, the dysfunction of these key genes could cause the defect in food preference observed in GS1189-strain larvae.     

Peptidomics of the larval Drosophila melanogaster central nervous system

Neuropeptides regulate most, if not all, biological processes in the animal kingdom, but only seven have been isolated and sequenced from Drosophila melanogaster. In analogy with the proteomics technology, where all proteins expressed in a cell or tissue are analyzed, the peptidomics approach aims at the simultaneous identification of the whole peptidome of a cell or tissue, i.e. all expressed peptides with their posttranslational modifications. Using nanoscale liquid chromatography combined with tandem mass spectrometry and data base mining, we analyzed the peptidome of the larval Drosophila central nervous system at the amino acid sequence level. We were able to provide biochemical evidence for the presence of 28 neuropeptides using an extract of only 50 larval Drosophila central nervous systems. Eighteen of these peptides are encoded in previously cloned or annotated precursor genes, although not all of them were predicted correctly. Eleven of these peptides were never purified before. Eight other peptides are entirely novel and are encoded in five different, not yet annotated genes. This neuropeptide expression profiling study also opens perspectives for other eukaryotic model systems, for which genome projects are completed or in progress.     

A lophotrochozoan twist gene is expressed in the ectomesoderm of the gastropod mollusk Patella vulgata

The twist gene is known to be involved in mesoderm formation in two of the three clades of bilaterally symmetrical animals: viz. deuterostomes (such as vertebrates) and ecdysozoans (such as arthropods and nematodes). There are currently no data on the spatiotemporal expression of this gene in the third clade, the lophotrochozoans (such as mollusks and annelids). To approach the question of mesoderm homology across bilaterians, we decided to analyze orthologs of this gene in the gastropod mollusk Patella vulgata that belongs to the lophotrochozoans. We present here the cloning, characterization, and phylogenetic analysis of a Patella twist ortholog, Pv-twi, and determine the early spatiotemporal expression pattern of this gene. Pv-twi expression was found in the trochophore larva in a subset of the ectomesoderm, one of the two sources of mesoderm in Patella. These data support the idea that twist genes were ancestrally involved in mesoderm differentiation. The absence of Pv-twi in the second mesodermal source, the endomesoderm, suggests that also other genes must be involved in lophotrochozoan mesoderm differentiation. It therefore remains a question if the mesoderm of all bilaterians is homologous.     

Roles of Hox genes in the patterning of the central nervous system of Drosophila

One of the key aspects of functional nervous systems is the restriction of particular neural subtypes to specific regions, which permits the establishment of differential segment-specific neuromuscular networks. Although Hox genes play a major role in shaping the anterior-posterior body axis during animal development, our understanding of how they act in individual cells to determine particular traits at precise developmental stages is rudimentary. We have used the abdominal leucokinergic neurons (ABLKs) to address this issue. These neurons are generated during both embryonic and postembryonic neurogenesis by the same progenitor neuroblast, and are designated embryonic and postembryonic ABLKs, respectively. We report that the genes of the Bithorax-Complex, Ultrabithorax (Ubx) and abdominal-A (abd-A) are redundantly required to specify the embryonic ABLKs. Moreover, the segment-specific pattern of the postembryonic ABLKs, which are restricted to the most anterior abdominal segments, is controlled by the absence of Abdominal-B (Abd-B), which we found was able to repress the expression of the neuropeptide leucokinin. We discuss this and other examples of how Hox genes generate diversity within the central nervous system of Drosophila.Keyword: development, Hox genes, central nervous system, Drosophila, cell fate specification     

Expression of AmphiCoe, an amphioxus COE/EBF gene, in the developing central nervous system and epidermal sensory neurons

The COE/EBF gene family marks a subset of prospective neurons in the vertebrate central and peripheral nervous system, including neurons deriving from some ectodermal placodes. Since placodes are often considered unique to vertebrates, we have characterised an amphioxus COE/EBF gene with the aim of using it as a marker to examine the timing and location of peripheral neuron differentiation. A single COE/EBF family member, AmphiCoe, was isolated from the amphioxus Branchiostoma floridae. AmphiCoe lies basal to the vertebrate COE/EBF genes in molecular phylogenetic analysis, suggesting that the duplications that formed the vertebrate COE/EBF family were specific to the vertebrate lineage. AmphiCoe is expressed in the central nervous system and in a small number of scattered ectodermal cells on the flanks of neurulae stage embryos. These cells become at least largely recessed beneath the ectoderm. Scanning electron microscopy was used to examine embryos in which the ectoderm had been partially peeled away. This revealed that these cells have neuronal morphology, and we infer that they are the precursors of epidermal primary sensory neurons. These characters lead us to suggest that differentiation of some ectodermal cells into sensory neurons with a tendency to sink beneath the embryonic surface represents a primitive feature that has become incorporated into placodes during vertebrate evolution.     

Towards gene therapy for the central nervous system

Gene therapy has generated enormous scientific, medical and public interest over the last decade. Clinical trials involving approximately 2000 patients worldwide have targeted simple genetic diseases such as cystic fibrosis, muscular dystrophy, adenosine deaminase deficiency, Gaucher's disease and familial hypercholesterolemia, as well as complex acquired diseases such as cancer and AIDS. The central nervous system is a new and particularly exciting target for gene therapy because its unique properties prevent the successful treatment of many neurological disorders by conventional means. This review discusses the potential applications of in vivo gene therapy to neurological disorders that have the greatest potential for genetic treatments.     

Expression of Frizzled10 in mouse central nervous system

Frizzled transmembrane proteins (Fzd) are receptors of Wnts, and they play key roles during central nervous system (CNS) development in vertebrates. Here we report the expression pattern of Frizzled10 in mouse CNS from embryonic stages to adulthood. Frizzled10 is expressed strongly at embryonic days E8.5 and E9.5 in the neural tube and tail bud. At E10.5, Frizzled10 is expressed in the forebrain vesicle, the fourth ventricle and the dorsal spinal cord. From E12.5 to E16.5, Frizzled10 expression is mainly observed in the cortical hem/fimbria, the neuroepithelium of the third ventricular zone, midbrain, developing cerebellum, and dorsal spinal cord. At P0, with the exception of expression in the fimbria, Frizzled10 mRNA expression is limited to specific nuclei including the ventral posterior thalamic nucleus (VP) and the dorsal lateral geniculate nucleus (DLG) in the developing thalamus as well as in the proliferative ventricular zone of the developing cerebellum. From P20 to adult, Frizzled10 mRNA is detected only in the internal capsule (ic). Our data show that expression of Frizzled10 is very strong during embryonic development of the CNS and suggest that Frizzled10 may play an essential role in spatial and temporal regulation during neural development.     

Sox neuro, a new Drosophila Sox gene expressed in the developing central nervous system

We describe the identification and detailed expression pattern of a second Drosophila Sox gene, SoxNeuro (SoxN), highly related to mammalian group B Sox1, 2, 3 genes. SoxN is expressed in a highly dynamic pattern during embyogenesis, being associated with the development of the central nervous system (CNS), from the early steps onwards. We present strong evidence that the early SoxN neuroectoderm expression is controlled by the zygotic dorso-ventral patterning genes (dpp, sog, brk, twi).     

5-HT-like immunoreactivity in the central nervous system of the crayfish,Pacifastacus leniusculus

An immunocytochemical technique with the use of three different antibodies raised against serotonin was applied to localize the immunoreactive neurons in the central nervous system of the crayfish, Pacifastacus leniusculus. Immunoreactive neurons were found in three optic ganglia (medulla externa, interna and terminalis). They appeared in three layers of the medulla externa and interna. The medulla terminalis displayed three prominent groups of immunoreactive perikarya and mainly marginal immunoreactive fibres. Immunoreactive areas of the brain comprised the protocerebral bridge, central body, paracentral lobes and two loci in the anterior portion of the protocerebrum, i.e., the terminal areas for immunoreactive fibres from the optic centres. The olfactory lobes showed a specific immunoreactive pattern. In addition, diffusely and sparsely distributed immunoreactive fibres were found throughout the brain. The immunoreactive neurons are largely localized in the same areas of the central nervous system as the catecholaminergic neurons although some distinct differences occur.     

Serotonin 5-HT3 receptors in the central nervous system

The 5-HT₃ receptor is a ligand-gated ion channel activated by serotonin (5-HT). Although originally identified in the peripheral nervous system, the 5-HT₃ receptor is also ubiquitously expressed in the central nervous system. Sites of expression include several brain stem nuclei and higher cortical areas such as the amygdala, hippocampus, and cortex. On the subcellular level, both presynaptic and postsynaptic 5-HT₃ receptors can be found. Presynaptic 5-HT₃ receptors are involved in mediating or modulating neurotransmitter release. Postsynaptic 5-HT₃ receptors are preferentially expressed on interneurons. In view of this specific expression pattern and of the well-established role of 5-HT as a neurotransmitter shaping development, we speculate that 5-HT₃ receptors play a role in the formation and function of cortical circuits.