LIFR beta plays a major role in neuronal identity determination and glial differentiation in the mouse facial nucleus.

In the hindbrain, generation of the facial nucleus involves complex developmental processes that will lead to the formation of a structure composed of motor neurons, astrocytes and oligodendrocytes. The implication of LIF-related cytokines in the development of this nucleus came to light with the analysis of mice mutant for the receptor of these cytokines, LIFR beta, which exhibit a massive loss of facial branchiomotor (fbm) neurons at birth and a severe decrease in GFAP expression, a marker of astrocytes. To uncover the cellular mechanisms regulated by LIFR beta during facial nucleus development, we first analyzed its expression pattern in the hindbrain. lifr beta is first expressed at E11.5 in the hindbrain neuroepithelium. The receptor is absent during the migration of fbm post-mitotic neurons but is strongly expressed when fbm neurons have reached rhombomere 6 at E12.5, and its expression is maintained until E18.5. From the analysis of lifr beta mutant embryos, we established that LIFR beta is necessary for fbm neurons' identity determination. We also show that LIFR beta is implicated in astrocyte and oligodendrocyte differentiation, specifically within the facial nucleus.

Abnormal mammary gland development in MMTV-CBLC transgenic mouse.

The CBL family of E3 ubiquitin ligases regulates cell signaling in a number of tissues by promoting degradation of tyrosine kinase receptors such as epidermal growth factor receptor. CBLC, the third member of the CBL family, is expressed in epithelial tissues, including the mammary gland. A transgenic mouse strain expressing a tetracyclin-inducible CBLC in the mammary gland was derived. It was found that CBLC transgene expression reduces the number and length of ducts during the development of the gland. In vivo results support the concept of CBLs as negative regulators of cell proliferation. Alternatively, the phenotype may be due to increased apoptosis. This mouse model may be used to further study regulatory components of the CBL pathway and may be crossed with mice susceptible to develop mammary tumors.

GDNF acts through PEA3 to regulate cell body positioning and muscle innervation of specific motor neuron pools.

Target innervation by specific neuronal populations involves still incompletely understood interactions between central and peripheral factors. We show that glial cell line-derived neurotrophic factor (GDNF), initially characterized for its role as a survival factor, is present early in the plexus of the developing forelimb and later in two muscles: the cutaneus maximus and latissimus dorsi. In the absence of GDNF signaling, motor neurons that normally innervate these muscles are mispositioned within the spinal cord and muscle invasion by their axons is dramatically reduced. The ETS transcription factor PEA3 is normally expressed by these motor neurons and fails to be induced in most of them in GDNF signaling mutants. Thus, GDNF acts as a peripheral signal to induce PEA3 expression in specific motor neuron pools thereby regulating both cell body position and muscle innervation.

Motoneuron death triggered by a specific pathway downstream of Fas. potentiation by ALS-linked SOD1 mutations.

Death pathways restricted to specific neuronal classes could potentially allow for precise control of developmental neuronal death and also underlie the selectivity of neuronal loss in neurodegenerative disease. We show that Fas-triggered death of normal embryonic motoneurons requires transcriptional upregulation of neuronal NOS and involves Daxx, ASK1, and p38 together with the classical FADD/caspase-8 cascade. No evidence for involvement of this pathway was found in cells other than motoneurons. Motoneurons from transgenic mice overexpressing ALS-linked SOD1 mutants (G37R, G85R, or G93A) displayed increased susceptibility to activation of this pathway: they were more sensitive to Fas- or NO-triggered cell death but not to trophic deprivation or excitotoxic stimulation. Thus, triggering of a motoneuron-restricted cell death pathway by neighboring cells might contribute to motoneuron loss in ALS.

Met signaling is required for recruitment of motor neurons to PEA3-positive motor pools.

Motor neurons in the spinal cord are grouped into motor pools, each of which innervates a single muscle. The ETS transcription factor PEA3 is a marker of a few such motor pools. Here, we show that pea3 is first induced by GDNF in a caudal subset of the motor neurons that will constitute the pea3+ population. Expansion of the pea3 domain subsequently occurs by recruitment of neurons from more anterior segments. Signaling by Met, the HGF receptor, is required for the rostral expansion of the pea3 domain, while the onset of pea3 expression is independent of met function. met expression is observed in pioneer neurons but does not precede that of pea3 in recruited neurons. We provide genetic evidence for a non-cell-autonomous function of met during the recruitment process. We propose the presence of a relay mechanism allowing cells induced by peripheral signals to recruit more anterior neurons to adopt the same motor pool-related phenotype.

[Towards an integrated cellular and molecular: definition of breast cancers]. / Les cancers du sein: vers un modèle cellulaire et moléculaire intégré

Breast cancer is a major health problem as well as scientifically poorly understood. Our knowledge of breast cancer is however rapidly progressing in several directions. First, genomic studies are establishing a new molecular classification of breast cancers. Molecular subtypes have been identified and are being associated with the histoclinical forms of breast cancers. Second, genetic alterations are discovered and classified, generating new potential therapeutical targets. Third, mammary stem cells have been identified in the normal mammary epithelium. Their altered counterparts have been identified in tumors and are being characterized. These combined studies allow a new integrated cellular and molecular definition of breast cancers and a conceptual basis that will help the management of the disease.

Cardiotrophin-like cytokine/cytokine-like factor 1 is an essential trophic factor for lumbar and facial motoneurons in vivo.

The ciliary neurotrophic factor alpha-receptor (CNTFRalpha) is required for motoneuron survival during development, but the relevant ligand(s) has not been determined. One candidate is the heterodimer formed by cardiotrophin-like cytokine (CLC) and cytokine-like factor 1 (CLF). CLC/CLF binds to CNTFRalpha and enhances the survival of developing motoneurons in vitro; whether this novel trophic factor plays a role in neural development in vivo has not been tested. We examined motor and sensory neurons in embryonic chicks treated with CLC and in mice with a targeted deletion of the clf gene. Treatment with CLC increased the number of lumbar spinal cord motoneurons that survived the cell death period in chicks. However, this effect was regionally specific, because brachial and thoracic motoneurons were unaffected. Similarly, newborn clf-/- mice exhibited a significant reduction in lumbar motoneurons, with no change in the brachial or thoracic cord. Clf deletion also affected brainstem motor nuclei in a regionally specific manner; the number of motoneurons in the facial but not hypoglossal nucleus was significantly reduced. Sensory neurons of the dorsal root ganglia were not affected by either CLC treatment or clf gene deletion. Finally, mRNA for both clc and clf was found in skeletal muscle fibers of embryonic mice during the motoneuron cell death period. These findings support the view that CLC/CLF is a target-derived factor required for the survival of specific pools of motoneurons. The in vivo actions of CLC and CLF can account for many of the effects of CNTFRalpha on developing motoneurons.

clc is co-expressed with clf or cntfr in developing mouse muscles.

BACKGROUND: The ciliary neurotrophic factor (CNTF) receptor is composed of two signalling receptor chains, gp130 and the leukaemia inhibitory factor receptor, associated with a non-signalling CNTF binding receptor alpha component (CNTFR). This tripartite receptor has been shown to play important roles in the development of motor neurons, but the identity of the relevant ligand(s) is still not clearly established. Recently, we have identified two new ligands for the CNTF receptor complex. These are heterodimeric cytokines composed of cardiotrophin-like cytokine (CLC) associated either with the soluble receptor subunit cytokine-like factor-1 (CLF) or the soluble form of the binding receptor itself (sCNTFR). RESULTS: Here we show that, during development, clc is expressed in lung, kidney, vibrissae, tooth, epithelia and muscles during the period of development corresponding to when motoneuron loss is observed in mice lacking a functional CNTF receptor. In addition, we demonstrate that it is co-expressed at the single cell level with clf and cntfr, supporting the idea that CLC might be co-secreted with either CLF or sCNTFR. CONCLUSION: This expression pattern is in favor of CLC, associated either with CLF or sCNTFR, being an important player in the signal triggered by the CNTF receptor being required for motoneuron development.

Identification of lynx2, a novel member of the ly-6/neurotoxin superfamily, expressed in neuronal subpopulations during mouse development.

We isolated a new gene which shares all the features of the Ly-6/neurotoxin superfamily, from gene organization to predicted 3D structure. As it is preferentially expressed in the nervous system, we called this gene lynx2, by analogy with lynx1, a nAChR modulator. In embryonic and postnatal mouse, lynx2 is expressed in postmitotic central and peripheral neurons. These include subpopulations of motor neurons, sensory neurons, interneurons and neurons of the autonomous nervous system. In addition, lynx2 is transiently expressed around the growing nerves in the limb bud. Comparison of its spatio-temporal expression pattern with that of two other members of this family, lynx1 and ly-6h, shows that these genes are detected both in distinct and overlapping neuron populations.

Synaptopodin and 4 novel genes identified in primary sensory neurons.

We performed differential gene expression profiling in the peripheral nervous system by comparing the transcriptome of sensory neurons with the transcriptome of lower motor neurons. Using suppression subtractive cDNA hybridization, we identified 5 anonymous transcripts with a predominant expression in sensory neurons. We determined the gene structures and predicted the functional protein domains. The 4930579P15Rik gene encodes for a novel inhibitor of protein phosphatase-1 and 9030217H17Rik was found to be the mouse gene synaptopodin. We performed in situ hybridization for all genes in mouse embryos, and found expression predominantly in the primary class of sensory neurons. Expression of 4930579P15Rik and synaptopodin was restricted to craniospinal sensory ganglia. Neither synaptopodin, nor any known family member of 4930579P15Rik, has ever been described in sensory neurons. The identification of protein domains and expression patterns allows further functional analysis of these novel genes in relation to the development and biology of sensory neurons.

Neuropoietin, a new IL-6-related cytokine signaling through the ciliary neurotrophic factor receptor.

A structural profile-based computational screen was used to identify neuropoietin (NP), a new cytokine. The np gene is localized in tandem with the cardiotrophin-1 gene on mouse chromosome 7. NP shares structural and functional features with ciliary neurotrophic factor (CNTF), cardiotrophin-1, and cardiotrophin-like cytokine. It acts through a membrane receptor complex comprising CNTF receptor-alpha component (CNTFRalpha), gp130, and leukemia inhibitory factor receptor to activate signal transducer and activator of transcription 3 signaling pathway. NP is highly expressed in embryonic neuroepithelia. Strikingly, CNTFRalpha, but not its alternate ligands, CNTF and cardiotrophin-like cytokine, is expressed at the same developmental stages. NP is also observed in retina and to a lesser extent in skeletal muscle. Moreover, NP could sustain the in vitro survival of embryonic motor neurons and could increase the proliferation of neural precursors when associated to epidermal growth factor and fibroblast growth factor 2. Thus, NP is a new ligand for CNTFRalpha, with important implications for murine nervous system development.