A genetic fusion GDNF-C fragment of tetanus toxin prolongs survival in a symptomatic mouse ALS model.

PURPOSE: Amyotrophic Lateral Sclerosis (ALS) is a paralyzing disorder that kills individuals within three to five years of onset without any possibility for effective treatment. One proposed therapy has been the use of neurotrophic factors to inhibit the apoptosis of motorneurones. At the present, one way to deliver neurotrophic factors after intramuscular injection to the motor neurones is through the use of adenoviral vectors. An alternative strategy is the use of the atoxic C fragment of tetanus toxin (TTC) as a neurotrophic factor carrier for motorneurones. METHODS: We have produced the recombinant protein fusion Glial Derived Neurotrophic Factor and C fragment of tetanus toxin (GDNF-TTC) and we have tested its antiapoptotic activity in degeneration culture cells and in the symptomatic SOD;{G93A} transgenic animal model for ALS. RESULTS: We demonstrated that GDNF-TTC induces the neuronal survival Akt kinase pathway in mouse cortical culture neurons and~maintains its antiapoptotic neuronal activity in Neuro2A cells. Moreover, we have found that genetic fusion is able to increase survival by 9 days and improves life quality in symptomatic ALS animal models. CONCLUSION: These results suggest that recombinant GDNF-TTC fusion protein intramuscular injections provide a potential therapy for ALS treatment.

Study of Fgf15 gene expression in developing mouse brain.

Fibroblast growth factor 15 (Fgf15) is a gene regulated by the expression of Otx2 in developing mouse brain (Proc Natl Acad Sci USA 97 (2000) 14388). Otx2 gene codes for a transcription factor and is fundamental for the regionalisation and development of the anterior neural plate and cephalic region of the vertebrate embryo (Development 124 (1997) 3639). In addition, the thalamic expression of Fgf15 has been recently reported under the control of Shh signalling gene, expressed in the diencephalic basal plate (Development 129 (2002) 4807). In the present work, we have analysed Fgf15 expression pattern during mouse neural development. Fgf15 appeared early in the developing neural epithelium, in domains where Fgf8 gene is also expressed and, at later stages, in specific groups of neural cells. Fgf8 is an important signalling protein with demonstrated morphogenetic activity in several embryonic regions. Fgf15 expression is localized, like Fgf8, in secondary neural tube organizers: the isthmic organizer (IsO) and the anterior neural ridge (ANR).

Analysis of Fgf15 expression pattern in the mouse neural tube.

The dynamic process of neural tube regionalization in vertebrates is regulated by the expression of developmental genes which appear in characteristic patterns at neuroepithelial transversal domains, which are called secondary organizers. The molecular code present in these neuroepithelial organizers controls the generation of morphogenetic signals that induce and maintain regional characteristics in the surrounding neuroepithelium. The product of the Fgf8 gene is a secreted protein that has been demonstrated to be the key molecule for the isthmic organizer and is also expressed in two other organizer regions: the zona limitans and the anterior neural ridge. Here we analyze the expression of Fgf15 at different stages of mouse development in relation to Fgf8 and Otx2 expression patterns.

Axial skeletal patterning in mice lacking all paralogous group 8 Hox genes.

We present a detailed study of the genetic basis of mesodermal axial patterning by paralogous group 8 Hox genes in the mouse. The phenotype of Hoxd8 loss-of-function mutants is presented, and compared with that of Hoxb8- and Hoxc8-null mice. Our analysis of single mutants reveals common features for the Hoxc8 and Hoxd8 genes in patterning lower thoracic and lumbar vertebrae. In the Hoxb8 mutant, more anterior axial regions are affected. The three paralogous Hox genes are expressed up to similar rostral boundaries in the mesoderm, but at levels that strongly vary with the axial position. We find that the axial region affected in each of the single mutants mostly corresponds to the area with the highest level of gene expression. However, analysis of double and triple mutants reveals that lower expression of the other two paralogous genes also plays a patterning role when the mainly expressed gene is defective. We therefore conclude that paralogous group 8 Hox genes are involved in patterning quite an extensive anteroposterior (AP) axial region. Phenotypes of double and triple mutants reveal that Hoxb8, Hoxc8 and Hoxd8 have redundant functions at upper thoracic and sacral levels, including positioning of the hindlimbs. Interestingly, loss of functional Hoxb8 alleles partially rescues the phenotype of Hoxc8- and Hoxc8/Hoxd8-null mutants at lower thoracic and lumbar levels. This suggests that Hoxb8 affects patterning at these axial positions differently from the other paralogous gene products. We conclude that paralogous Hox genes can have a unique role in patterning specific axial regions in addition to their redundant function at other AP levels.

Otx2 is required for visceral endoderm movement and for the restriction of posterior signals in the epiblast of the mouse embryo.

Genetic and embryological experiments have demonstrated an essential role for the visceral endoderm in the formation of the forebrain; however, the precise molecular and cellular mechanisms of this requirement are poorly understood. We have performed lineage tracing in combination with molecular marker studies to follow morphogenetic movements and cell fates before and during gastrulation in embryos mutant for the homeobox gene Otx2. Our results show, first, that Otx2 is not required for proliferation of the visceral endoderm, but is essential for anteriorly directed morphogenetic movement. Second, molecules that are normally expressed in the anterior visceral endoderm, such as Lefty1 and Mdkk1, are not expressed in Otx2 mutants. These secreted proteins have been reported to antagonise, respectively, the activities of Nodal and Wnt signals, which have a role in regulating primitive streak formation. The visceral endoderm defects of the Otx2 mutants are associated with abnormal expression of primitive streak markers in the epiblast, suggesting that anterior epiblast cells acquire primitive streak characteristics. Taken together, our data support a model whereby Otx2 functions in the anterior visceral endoderm to influence the ability of the adjacent epiblast cells to differentiate into anterior neurectoderm, indirectly, by preventing them from coming under the influence of posterior signals that regulate primitive streak formation.

Gene expression profiles in normal and Otx2-/- early gastrulating mouse embryos.

The mouse Otx2 gene is a homeobox transcription factor required as early as gastrulation for the proper development of the head. We compared gene expression profiles in wild-type and Otx2(-/-) 6.5 days postcoitum embryos by using a serial analysis of gene expression assay adapted to microdissected structures. Among a broader list, the study of six genes found to be differentially expressed allows defining a role for Otx2 in the orchestration of cell movements leading to the adequate organization of the embryo before gastrulation.

Chimeric green fluorescent protein-aequorin as bioluminescent Ca2+ reporters at the single-cell level.

Monitoring calcium fluxes in real time could help to understand the development, the plasticity, and the functioning of the central nervous system. In jellyfish, the chemiluminescent calcium binding aequorin protein is associated with the green fluorescent protein and a green bioluminescent signal is emitted upon Ca(2+) stimulation. We decided to use this chemiluminescence resonance energy transfer between the two molecules. Calcium-sensitive bioluminescent reporter genes have been constructed by fusing green fluorescent protein and aequorin, resulting in much more light being emitted. Chemiluminescent and fluorescent activities of these fusion proteins have been assessed in mammalian cells. Cytosolic Ca(2+) increases were imaged at the single-cell level with a cooled intensified charge-coupled device camera. This bifunctional reporter gene should allow the investigation of calcium activities in neuronal networks and in specific subcellular compartments in transgenic animals.

Hematopoietic progenitor cell abnormalities in Hoxc-8 null mutant mice.

The mammalian Hox genes encode a family of conserved transcription factors that control the establishment of the body plan during embryogenesis. Many Hox genes are also known to be expressed in hematopoietic cells. We found that Hoxc-8, a member of the Hox C cluster, is expressed in the mouse hematopoietic organs, fetal liver and adult bone marrow. To determine the role of Hoxc-8 gene in hematopoiesis, we compared progenitor cell numbers in the fetal liver and adult bone marrow cells. We observed a significant reduction in the number of erythroid burst-forming unit (BFU-E) and in granulocyte/macrophage colony-forming unit (CFU-GM) in the Hoxc-8 null mice, although the peripheral blood cell counts were normal. The hematopoietic cells from the homozygote animals exhibited normal expansion capability in a liquid culture system, suggesting that the decreased number of progenitor cells may be due to a defect extrinsic to the hematopoietic cells, such as in the interaction with the microenvironment.

A somatic gene transfer approach using recombinant fusion proteins to map muscle-motoneuron projections in Xenopus spinal cord.

A combination of somatic gene transfer with fusion protein technology has been developed, thus providing an innovative means of mapping muscle-motoneuronal connections in Xenopus tadpole spinal cord. We analyzed whether a neuronal tracer created by the fusion of the LacZ gene to the tetanus toxin C fragment (LacZ-TTC) could be produced from plasmid DNA injected into muscle, and whether it could be released and undergo retrograde transport into motoneurons. Plasmids encoding various fusion protein constructions, with or without a signal peptide, were injected into dorsal or caudal muscles of premetamorphic tadpoles. The marker was produced in the muscle at constantly high levels. At one month post-injection, the fusion protein passed the neuromuscular junction and underwent retrograde transport into motoneurons. Transfer into motoneurons was seen for every animal injected, emphasizing the high reproducibility and efficiency of the process. No uptake of beta-gal protein into motoneurons was observed in the absence of the TTC fragment. Furthermore, no enhancement was obtained by adding a signal peptide. These results provide the first demonstration of the synthesis and transport of a TTC fusion protein produced directly from exogenous DNA in a vertebrate system.

Cortical neurons require Otx1 for the refinement of exuberant axonal projections to subcortical targets.

Information processing in the nervous system depends on the creation of specific synaptic connections between neurons and targets during development. The homeodomain transcription factor Otx1 is expressed in early-generated neurons of the developing cerebral cortex. Within layer 5, Otx1 is expressed by neurons with subcortical axonal projections to the midbrain and spinal cord. Otx1 is also expressed in the precursors of these neurons, but is localized to the cytoplasm. Nuclear translocation of Otx1 occurs when layer 5 neurons enter a period of axonal refinement and eliminate a subset of their long-distance projections. Otx1 mutant mice are defective in the refinement of these exuberant projections, suggesting that Otx1 is required for the development of normal axonal connectivity and the generation of coordinated motor behavior.

Transient dwarfism and hypogonadism in mice lacking Otx1 reveal prepubescent stage-specific control of pituitary levels of GH, FSH and LH.

Genetic and molecular approaches have enabled the identification of regulatory genes critically involved in determining cell types in the pituitary gland and/or in the hypothalamus. Here we report that Otx1, a homeobox-containing gene of the Otx gene family, is postnatally transcribed and translated in the pituitary gland. Cell culture experiments indicate that Otx1 may activate transcription of the growth hormone (GH), follicle-stimulating hormone (betaFSH), luteinizing hormone (betaLH) and alpha-glycoprotein subunit (alphaGSU) genes. Analysis of Otx1 null mice indicates that, at the prepubescent stage, they exhibit transient dwarfism and hypogonadism due to low levels of pituitary GH, FSH and LH hormones which, in turn, dramatically affect downstream molecular and organ targets. Nevertheless, Otx1-/- mice gradually recover from most of these abnormalities, showing normal levels of pituitary hormones with restored growth and gonadal function at 4 months of age. Expression patterns of related hypothalamic and pituitary cell type restricted genes, growth hormone releasing hormone (GRH), gonadotropin releasing hormone (GnRH) and their pituitary receptors (GRHR and GnRHR) suggest that, in Otx1-/- mice, hypothalamic and pituitary cells of the somatotropic and gonadotropic lineages appear unaltered and that the ability to synthesize GH, FSH and LH, rather than the number of cells producing these hormones, is affected. Our data indicate that Otx1 is a new pituitary transcription factor involved at the prepubescent stage in the control of GH, FSH and LH hormone levels and suggest that a complex regulatory mechanism might exist to control the physiological need for pituitary hormones at specific postnatal stages.

Structure and expression of Wnt13, a novel mouse Wnt2 related gene.

We have identified a novel mouse member of the Wnt family, Wnt13. Among mouse Wnt genes, Wnt13 is most closely related to Wnt2. Sequence comparisons and chromosomal localization strongly suggest that Wnt13, rather than Wnt2, is the mouse orthologue of both the human WNT13 and Xenopus XWnt2 genes. Wnt13 is expressed in the embryonic mesoderm during gastrulation. At later stages, transcripts are detected in the dorsal midline of the diencephalon and mesencephalon, the heart primordia, the periphery of the lung bud and the otic and optic vesicles. These data suggest that Wnt13 function might partially overlap with those of other Wnt genes in the cell signaling mechanisms controlling mesoderm specification during gastrulation and some aspects of brain, heart and lung formation.

Increased apoptosis of motoneurons and altered somatotopic maps in the brachial spinal cord of Hoxc-8-deficient mice.

Mice deficient for the homeotic gene Hoxc-8 suffer from a congenital prehension deficiency of the forepaw. During embryogenesis, Hoxc-8 is highly expressed in motoneurons within spinal cord segments C7 to T1. These motoneurons innervate forelimb distal muscles that move the forepaw. In Hoxc-8 mutant embryos, formation of these muscles is normal, but their innervation is perturbed. From E13.5 onwards, distal muscles normally supplied by C(7-8) MNs also receive ectopic projections from C(5-6) and T1 motoneurons. Coordinates of motor pools are altered along the rostrocaudal and also the mediolateral axes. Following this aberrant connectivity pattern and during the time of naturally occurring cell death, apoptosis is specifically enhanced in C7-T1 motoneurons. Loss of Hox-encoded regional specifications subsequently leads to a numerical deficit of motoneurons and an irreversible disorganization of motor pools. In Hoxc-8 null mutants, C(7-8) motoneurons lose their selective advantage in growth cone pathfinding behavior and/or target recognition, two essential steps in the establishment and maintenance of a functional nervous system.

Construction of hybrid proteins that migrate retrogradely and transynaptically into the central nervous system.

The nontoxic proteolytic C fragment of tetanus toxin (TTC peptide) has the same ability to bind nerve cells and be retrogradely transported through a synapse as the native toxin. We have investigated its potential use as an in vivo neurotropic carrier. In this work we show that a hybrid protein encoded by the lacZ-TTC gene fusion retains the biological functions of both proteins in vivo-i.e. , retrograde transynaptic transport of the TTC fragment and beta-galactosidase enzymatic activity. After intramuscular injection, enzymatic activity could be detected in motoneurons and connected neurons of the brainstem areas. This strategy could be used to deliver a biological activity to neurons from the periphery to the central nervous system. Such a hybrid protein could also be used to map synaptic connections between neural cells.

Role of leukemia inhibitory factor during mammalian development.

Leukemia inhibitory factor (LIF) is a cytokine that exhibits proliferative, survival and differentiation activities on a wide range of cell types. A role for LIF in embryonic development is suggested by: i) its ability to stimulate the proliferation of embryonic stem (ES) cells in vitro, while maintaining their totipotency and ii) by both its maternal and embryonic expression at the time of blastocyst implantation. Functional studies of LIF and its receptor during mouse embryogenesis have been performed using the techniques of targeted gene replacement and transgene expression in ES cells to produce transgenic mice bearing either loss- or gain-of-function mutations for LIF activity. Whereas, the phenotype observed in the LIF gain-of-function mutant mice supports a role for LIF in early embryogenesis, the loss-of-function phenotypes point to more specialized functions for LIF in development and further reveal the redundant feature of the LIF cytokine/receptor family.

Influence of leukemia inhibitory factor on galanin/GMAP and neuropeptide Y expression in mouse primary sensory neurons after axotomy.

The effect of unilateral transection of the sciatic nerve on expression of immunoreactive galanin (GAL), galanin-message-associated peptide (GMAP) and neuropeptide tyrosine (NPY) in dorsal root ganglia (DRGs) was studied in wild-type mice and in leukemia inhibitory factor (LIF)-deficient mice. In normal and contralateral DRGs small numbers of weakly fluorescent GAL- and GMAP-positive neuronal cell bodies and numerous positive fibers were observed. No NPY-positive cell bodies but a few fibers surrounding blood vessels were seen. In LIF deficient mice hardly any GAL- or GMAP-positive neurons or fibers were seen, nor was NPY-like immunoreactivity present in cell bodies. After axotomy there was a dramatic upregulation of all three peptides in wild-type DRG neurons, whereby 50-60% of the neuron profiles, encompassing both small and large profiles, were GAL- and GMAP-immunoreactive (IR). About one third of all neuron profiles, mainly large ones, were NPY-positive. In LIF-deficient mice this upregulation was much less pronounced. Thus GAL- and GMAP-IR neuron profiles were reduced by 65-70% compared with the wild-type mice. The number of NPY-positive neuron profiles was reduced to half but this difference was not significant. There was also an ipsilateral decrease in fluorescence intensity for all three peptide immunoreactivities in the LIF-deficient mice as compared with wild-type mice after axotomy. There was no apparent difference in size between, respectively, GAL- and GMAP-positive profiles when comparing LIF-deficient and wild-type mice before or after axotomy. There were, however, no small NPY-IR profiles in the LIF-deficient group. The present results suggests that LIF is important for the dramatic upregulation of GAL and GMAP seen after axotomy. It may also be important for the normal expression of galanin in mouse DRGs, since wild-type mice seemed to have somewhat more positive cell bodies and more fluorescent fibers. LIF seems to be less important for the control of NPY synthesis, but may be involved in NPY regulation in small-sized neurons.

Epilepsy and brain abnormalities in mice lacking the Otx1 gene.

The morphogenesis of the brain and the differentiation of the neural structures are highly complex processes. A series of temporally and spatially regulated morphogenetic events gives rise to smaller areas that are phylogenetically, functionally and often morphogenetically different. Candidate genes for positional information and differentiation during morphogenesis have been isolated. Both in vivo inactivation in mice and impairment in human diseases revealed, that they are required in regional specification and/or correct cell-type induction. We have previously cloned and characterized the murine Otx1 gene, which is related to orthodenticle (otd), a homeobox-containing gene required for Drosophila head development. Expression data during murine embryogenesis and postnatal brain development support the idea that Otx1 could be required for correct brain and sense organs development. To decipher its role in vivo we produced null mice by replacing Otx1 with the lacZ gene. Otx1-/- mice showed spontaneous epileptic behaviour and multiple abnormalities affecting mainly the telencephalic temporal and perirhinal areas, the hippocampus, the mesencephalon and the cerebellum, as well as the acoustic and visual sense organs. Our findings indicate that the Otx1 gene product is required for proper brain functions.

Cryptic physiological trophic support of motoneurons by LIF revealed by double gene targeting of CNTF and LIF.

BACKGROUND: The survival and differentiation of motoneurons during embryonic development, and the maintenance of their function in the postnatal phase, are regulated by a great variety of neurotrophic molecules which mediate their effects through different receptor systems. The multifactorial support of motoneurons represents a system of high security, because the inactivation of individual ligands has either no detectable, or relatively small, atrophic or degenerative effect on motoneurons. RESULTS: Leukaemia inhibitory factor (LIF) has been demonstrated to support motoneuron survival in vitro and in vivo under different experimental conditions. However, when LIF was inactivated by gene targeting, there were no apparent changes in the number and structure of motoneurons and no impairment of their function. The slowly appearing, relatively mild degenerating effects in motoneurons that resulted from ciliary neurotrophic factor (CNTF) gene targeting were substantially potentiated by simultaneous inactivation of the LIF gene, however. Thus, in mice deficient in LIF and CNTF, the degenerative changes in motoneurons were more extensive and appeared earlier. These changes were also functionally reflected by a marked reduction in grip strength. CONCLUSIONS: Degenerative disorders of the nervous system, in particular those of motoneurons, may be based on multifactorial inherited and/or acquired defects which individually do not result in degenerative disorders, but which become apparent when additional (cryptic) inherited disturbances or sub-threshold concentrations of noxious factors come into play. Accordingly, the inherited inactivation of the CNTF gene in a high proportion of the Japanese population may represent a predisposing factor for degenerative disorders of motoneurons.

Forebrain and midbrain regions are deleted in Otx2-/- mutants due to a defective anterior neuroectoderm specification during gastrulation.

We have replaced part of the mouse homeogene Otx2 coding region with the E. coli lacZ coding sequence, thus creating a null allele of Otx2. By 9.5 dpc, homozygous mutant embryos are characterized by the absence of forebrain and midbrain regions. From the early to midstreak stages, endomesodermal cells expressing lacZ fail to be properly localized anteriorly. In the ectodermal layer, lacZ transcription is progressively extinguished, being barely detectable by the late streak stage. These data suggest that Otx2 expression in endomesoderm and ectoderm is required for anterior neuroectoderm specification. In gastrulating heterozygous embryos, a post-transcriptional repression acts on lacZ transcripts in the ectoderm, but not in the external layer, suggesting that different post-transcriptional mechanisms control Otx2 expression in both layers.