Potent activation of FGF-2 IRES-dependent mechanism of translation during brain development

Fibroblast growth factor-2 (FGF-2) plays a fundamental role in brain functions. This role may be partly achieved through the control of its expression at the translational level via an internal ribosome entry site (IRES)-dependent mechanism. Transgenic mice expressing a bicistronic mRNA allowed us to study in vivo and ex vivo where this translational mechanism operates. Along brain development, we identified a stringent spatiotemporal regulation of FGF-2 IRES activity showing a peak at post-natal day 7 in most brain regions, which is concomitant with neuronal maturation. At adult age, this activity remained relatively high in forebrain regions. By the enrichment of this activity in forebrain synaptoneurosomes and by the use of primary cultures of cortical neurons or cocultures with astrocytes, we showed that this activity is indeed localized in neurons, is dependent on their maturation, and correlates with endogenous FGF-2 protein expression. In addition, this activity was regulated by astrocyte factors, including FGF-2, and spontaneous electrical activity. Thus, neuronal IRES-driven translation of the FGF-2 mRNA may be involved in synapse formation and maturation.     

Overexpression of the Promigratory and Prometastatic PTK7 Receptor Is Associated with an Adverse Clinical Outcome in Colorectal Cancer

Biomarkers and novel therapeutic targets are urgently needed in colorectal cancer (CRC). The pseudo tyrosine kinase receptor 7 (PTK7) is involved in planar cell polarity and it is deregulated in various malignancies, including CRC. Yet, little is known about its protein expression in human CRC, or about a possible correlation of its expression with clinical endpoints. Using a clinically annotated Tissue MicroArray (TMA) produced from from 192 consecutive CRC patients treated by initial surgery, we examined PTK7 expression by immunohistochemistry in tumoral tissue and matched normal mucosae, and correlated its expression with clinico-pathological features and patient outcome. PTK7 depletion by specific shRNA in HCT116 and HCT15 CRC cell lines was found to affect cell proliferation, resistance to drugs and cell migration. Tumor growth and metastatic phenotype were investigated in vivo using a xenograft mouse model of CRC cells with modulated expression of PTK7 levels. PTK7 was significantly up-regulated in CRC tissue as compared to matched healthy mucosae, and significant overexpression was found in 34% of patients. PTK7 overexpression was significantly associated with a reduced metastasis-free survival in non-metastatic patients. In HCT116 and HCT15 cells, shRNA PTK7 reduced migration but did not affect cell proliferation and resistance to drugs. In a xenograft mouse of HCT15 cells, downregulation of PTK7 led to reduced tumor growth, whereas its overexpression in PTK7-negative cancer cells led to increased metastatic events. PTK7 expression thus represents a potential prognostic biomarker and a novel therapeutic target in CRC.     

Embryonic stem cells and cell replacement therapies in the nervous system

Embryonic stem (ES) cells are pluripotential cells derived from the pre-implantation embryo. They can proliferate indefinitely in vitro while retaining pluripotency. ES cells can also be made to differentiate into a large variety of cell types in vitro. This has paved the way to research aimed at using ES-derived cells for cell replacement therapies. Hence, mouse ES cells can efficiently differentiate into neural precursors which can further generate functional neurons, astrocytes, and oligodendrocytes. Methods have also been developed to coax mouse ES-derived neural stem cells to differentiate into either dopaminergic neurons or motoneurons. Mouse ES-derived neural stem cells, or their fully differentiated progeny, have been shown to survive, integrate, and to some extent, function following transplantation within appropriate rodent host tissue. Research on human ES cells is still in its infancy. Considerable work has to be done: (1) to master growth and genetic manipulation of human ES cells; (2) to master their differentiation into specific cell types; and (3) to demonstrate that they can provide long term therapeutical benefits upon grafting into damaged tissues in humans. From the ethical point of view, the establishment of appropriate primate model will be an obligatory prerequisite to clinical trials based on ES cells derivatives grafting.     

The GCN2 kinase biases feeding behavior to maintain amino acid homeostasis in omnivores

To insure an adequate supply of nutrients, omnivores choose among available food sources. This process is exemplified by the well-characterized innate aversion of omnivores to otherwise nutritious foods of imbalanced amino acid content. We report that brain-specific inactivation of GCN2, a ubiquitously expressed protein kinase that phosphorylates translation initiation factor 2 alpha (eIF2alpha) in response to intracellular amino acid deficiency, impairs this aversive response. GCN2 inactivation also diminishes phosphorylated eIF2alpha levels in the mouse anterior piriform cortex following consumption of an imbalanced meal. An ancient intracellular signal transduction pathway responsive to amino acid deficiency thus affects feeding behavior by activating a neuronal circuit that biases consumption against imbalanced food sources.     

Chalcone synthase activity and polyphenolic compounds of shoot tissues from adult and rejuvenated walnut trees

Changes in the metabolism of naphthoquinone and flavonoids during the growth of half-sib adult and rejuvenated walnut shoots (Juglans nigra × Juglans regia L.) were studied at the tissue level for two years after pruning. Moreover, the role of chalcone synthase (CHS; EC 2.3.1.74) in the regulation of flavonoid biosynthesis was investigated at the level of enzyme activity. The end products of walnut flavonoid biosynthesis, myricitrin and quercitrin, which accumulated in the bark and phloem at the end of growth, did not inhibit the biosynthetic process at concentrations of up to 100 μM each. There was no evidence of CHS regulation by feedback or similar mechanisms which might modulate enzyme activity. Mathematical correlation of CHS activity and flavonoid accumulation during shoot growth, however, indicated that CHS is the rate-limiting enzyme of the pathway in bark and phloem and that flavonoids seem to be transported from phloem to bark where they accumulated mainly during growth. In defoliated shoots, naphthoquinone metabolism appeared to be a marker of the walnut rejuvenation stage in the medulla, phloem and buds immediately after cutting and thereafter mainly in buds one year after cutting. Chalcone synthase and flavonoid contents appeared to be markers of the adult stage in the phloem. Received: 30 September 1996 / Accepted: 17 March 1997     

N-linked oligosaccharide processing is not necessary for glycoprotein secretion in plants

The role of N-glycans in the secretion of glycoproteins by suspension-cultured sycamore cells was studied. The transport of glycoproteins to the extracellular compartment was investigated in the presence of a glycan-processing inhibitor, castanospermine. Castanospermine has been selected because it inhibits homogeneously glycan maturation in sycamore cells and leads to the accumulation of a single immature N-glycan. The structure of this glycan has been identified as Glc₃Man₇GlcNAc₂ by labeling experiments, affinity chromatography on concanavalin A-Sepharose and proton NMR. In contrast with previous results showing that N-glycosylation is a pre-requisite for secretion of N-linked glycoproteins, this secretion is not affected by the presence of castanospermine. As a consequence, the presence of this unprocessed glycan is sufficient for an efficient secretion of glycoproteins in the extracellular compartment of suspension-cultured sycamore cells.     

N-Glycoprotein biosynthesis in plants: recent developments and future trends

N-glycosylation is a major modification of proteins in plant cells. This process starts in the endoplasmic reticulum by the co-translational transfer of a precursor oligosaccharide to specific asparagine residues of the nascent polypeptide chain. Processing of this oligosaccharide into high-mannose-type, paucimannosidic-type, hybrid-type or complex-type N-glycans occurs in the secretory pathway as the glycoprotein moves from the endoplasmic reticulum to its final destination. At the end of their maturation, some plant N-glycans have typical structures that differ from those found in their mammalian counterpart by the absence of sialic acid and the presence of (1,2)-xylose and (1,3)-fucose residues. Glycosidases and glycosyltransferases that respectively catalyse the stepwise trimming and addition of sugar residues are generally considered as working in a co-ordinated and highly ordered fashion to form mature N-glycans. On the basis of this assembly line concept, fast progress is currently made by using N-linked glycan structures as milestones of the intracellular transport of proteins along the plant secretory pathway. Further developments of this approach will need to more precisely define the topological distribution of glycosyltransferases within a plant Golgi stack. In contrast with their acknowledged role in the targeting of lysosomal hydrolases in mammalian cells, N-glycans have no specific function in the transport of glycoproteins into the plant vacuole. However, the presence of N-glycans, regardless of their structures, is necessary for an efficient secretion of plant glycoproteins. In the biotechnology field, transgenic plants are rapidly emerging as an important system for the production of recombinant glycoproteins intended for therapeutic purposes, which is a strong motivation to speed up research in plant glycobiology. In this regard, the potential and limits of plant cells as a factory for the production of mammalian glycoproteins will be illustrated.     

Mother’s Emotional and Posttraumatic Reactions after a Preterm Birth: The Mother-Infant Interaction Is at Stake 12 Months after Birth

Objectives

Very preterm infants are known to be at risk of developmental disabilities and behavioural disorders. This condition is supposed to alter mother-infant interactions. Here we hypothesize that the parental coping with the very preterm birth may greatly influence mother-infant interactions.

Methods

100 dyads were included in 3 university hospitals in France. Preterm babies at higher risk of neurodevelopmental sequelae (PRI>10) were excluded to target the maternal determinants of mother-infant interaction. We report the follow-up of this cohort during 1 year after very preterm birth, with regular assessment of infant somatic state, mother psychological state and the assessment of mother-infant interaction at 12 months by validated scales (mPPQ, HADS, EPDS, PRI, DDST and PIPE).

Results

We show that the intensity of post-traumatic reaction of the mother 6 months after birth is negatively correlated with the quality of mother-infant interaction at 12 months. Moreover, the anxious and depressive symptoms of the mother 6 and 12 months after birth are also correlated with the quality of mother-infant interaction at 12 months. By contrast, this interaction is not influenced by the initial affective state of the mother in the 2 weeks following birth. In this particular population of infants at low risk of sequelae, we also show that the quality of mother-infant interaction is not correlated with the assessment of the infant in the neonatal period but is correlated with the fine motor skills of the baby 12 months after birth.

Conclusions

This study suggests that mothers’ psychological condition has to be monitored during the first year of very preterm infants’ follow-up. It also suggests that parental interventions have to be proposed when a post-traumatic, anxious or depressive reaction is suspected.