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Monocular deprivation (MD) is a well-known paradigm of experience-dependent plasticity in which cortical neurons exhibit a shift of ocular dominance (OD) toward the open eye. The mechanisms underlying this form of plasticity are incompletely understood. Here we demonstrate the involvement of callosal connections in the synaptic modifications occurring during MD. Rats at the peak of the critical period were deprived for 7 days, resulting in the expected OD shift toward the open eye. Acute microinjection of the activity blocker muscimol into the visual cortex contralateral to the recording site restored binocularity of cortical cells. Continuous silencing of callosal input throughout the period of MD also resulted in substantial attenuation of the OD shift. Blockade of interhemispheric communication selectively enhanced deprived eye responses with no effect on open eye-driven activity. We conclude that callosal inputs play a key role in functional weakening of less active connections during OD plasticity.

An important feature of the cerebral cortex is its layered organization, which is modulated in an area-specific manner. We found that the transcription factor AP2gamma regulates laminar fate in a region-specific manner. Deletion of AP2gamma (also known as Tcfap2c) during development resulted in a specific reduction of upper layer neurons in the occipital cortex, leading to impaired function and enhanced plasticity of the adult visual cortex. AP2gamma functions in apical progenitors, and its absence resulted in mis-specification of basal progenitors in the occipital cortex at the time at which upper layer neurons were generated. AP2gamma directly regulated the basal progenitor fate determinants Math3 (also known as Neurod4) and Tbr2, and its overexpression promoted the generation of layer II/III neurons in a time- and region-specific manner. Thus, AP2gamma acts as a regulator of basal progenitor fate, linking regional and laminar specification in the mouse developing cerebral cortex.

Exposure to an enriched environment has proven to be beneficial in the recovery of function after brain lesions, but the underlying mechanisms remain only partly understood. One possibility is that environmental enrichment stimulates the reorganization of areas and fiber tracts that have been spared by the injury. Here we evaluate the effects of enriched environment on the sprouting of undamaged retinal afferents into the deafferented superior colliculus (SC) after a partial retinal lesion in adult rats. Anterograde tracing of retinal axons demonstrated a significant increase in fiber sprouting in the denervated SC of animals reared in enriched environment compared to animals reared in standard conditions. Environmental enrichment also promoted a substantial recovery of synaptic sites within the deafferented SC as shown by both synapsin I and vesicular glutamate transporter 2 immunostaining. These data provide evidence that environmental enrichment stimulates axonal plasticity and synaptic reorganization following brain injury.

Molecular markers derived from resistance gene analogs of HcrVf2, the first apple resistance gene cloned, may pave the way to the cloning of additional apple scab resistance genes. The Malus xdomestica 'Florina' (Vf) bacterial artificial chromosome (BAC) genomic library was screened by hybridization using HcrVf2 as a probe. Positive BAC clones were assembled into contigs and microsatellite markers developed from each contig mapped. Only linkage groups 1 and 6 contained HcrVf2 paralogs. On linkage group 1, five loci in addition to the Vf locus were identified. A single locus was detected on linkage group 6. Representative BAC clones of these loci including the Vf locus were sequenced and the gene structure compiled. A total of 22 sequences, showing high sequence similarity to HcrVf2, were identified. Nine sequences were predicted to encode all seven protein domains described in HcrVf2, while three were truncated. Transcriptional analysis indicated that six genes with a complete HcrVf-like structure were constitutively expressed in young uninfected leaves of 'Florina'. The map position of each HcrVf analog was compared with the location of the major apple scab resistance genes. None of the major genes conferring scab resistance co-localized with HcrVf paralogs, indicating that they are unlikely to belong to the leucine-rich repeat - transmembrane class, which includes the Vf gene.

In order to unravel the genetic architecture underlying plant response to drought, we adopted an integrated approach, combining transcript profiling and quantitative trait loci (QTL) mapping. In fact, improving plant tolerance to water stress is an important, but, at the same time, a difficult task, since plant tolerance is the result of many complex mechanisms acting at different levels of plant organization, and its genetic basis is largely unknown. The phenotypic data, concerning yield components and flowering time, of a population of 142 maize Recombinant Inbred Lines (RILs), grown under well watered conditions or under water stress, were submitted to linkage analysis to detect drought-tolerance QTLs. Thirty genomic regions containing 50 significant QTLs distributed on nine chromosomes were identified. At the same time, a customized targeted oligoarray was used to monitor the expression levels of 1,000 genes, representative of the immature maize kernel transcriptome. Using this DNA array we compared transcripts from 10 days after pollination kernels of two susceptible and two drought tolerant genotypes (extracted from our RILs) grown under control and water stress field conditions. Two hundred and fifty-two genes were significantly affected by stress in at least one genotype. From a set of these, 49 new molecular markers were developed. By mapping most of them and by in silico mapping other regulated sequences, 88 differentially expressed genes were localized onto our linkage map, which, added to the existing 186 markers, brought their total number on the map to 274. Twenty-two of the 88 differentially expressed genes mapped in the same chromosomal segments harbouring QTLs for tolerance, thus representing candidate genes for further functional studies.

The exploitation of heterosis is one of the most outstanding advancements in plant breeding, although its genetic basis is not well understood yet. This research was conducted on the materials arising from the maize single cross B73 x H99 to study heterosis by procedures of classical genetic and quantitative trait loci (QTL) analyses. Materials were the basic generations, the derived 142 recombinant inbred lines (RILs), and the three testcross populations obtained by crossing the 142 RILs to each parent and their F(1). For seedling weight (SW), number of kernels per plant (NK), and grain yield (GY), heterosis was >100% and the average degree of dominance was >1. Epistasis was significant for SW and NK but not for GY. Several QTL were identified and in most cases they were in the additive-dominance range for traits with low heterosis and mostly in the dominance-overdominance range for plant height (PH), SW, NK, and GY. Only a few QTL with digenic epistasis were identified. The importance of dominance effects was confirmed by highly significant correlations between heterozygosity level and phenotypic performance, especially for GY. Some chromosome regions presented overlaps of overdominant QTL for SW, PH, NK, and GY, suggesting pleiotropic effects on overall plant vigor.

In recent years, microRNAs (miRNAs) have polarized the interest of the scientific community as a new category of gene expression regulators, present in both plants and animals. Plant miRNAs are involved in processes such as plant development, organ identity, and stress response. Nonetheless, knowledge of their functions is still incomplete, and it is conceivable that further new processes in which they are involved will be discovered. For these reasons, structural and functional characterization of MIR genes, that are also in crop species such as Zea mays L., becomes instrumental in addressing genetic and molecular mechanisms controlling phenotype determination and phenotypic adaptation to growing conditions. The present study contributes to the characterization of five miRNA families in maize, from the determination of their expression pattern in different maize tissues and genotypes, to the identification of putative targets by bioinformatic means and subsequent experimental validation of three targets by modified 5' RACE experiments. Furthermore, 30 different MIR genes belonging to these five miRNA families were analysed by their attribution to maize chromosomes using oat-maize addition lines and by investigating their phylogenetic relationship with genes from other cereals. In particular, sequence homology was determined by the reciprocal best BLAST hit approach, to define groups of homologous genes between maize, rice, and sorghum.

Visual deprivation such as dark rearing (DR) prolongs the critical period for ocular dominance plasticity and retards the maturation of gamma-aminobutyric acid (GABA)ergic inhibition in visual cortex. The molecular signals that mediate the effects of DR on the development of visual cortex are not well defined. To test the role of brain-derived neurotrophic factor (BDNF), we examined the effects of DR in transgenic mice in which BDNF expression in visual cortex was uncoupled from visual experience and remained elevated during DR. In dark-reared transgenic mice, visual acuity, receptive field size of visual cortical neurons, critical period for ocular dominance plasticity, and intracortical inhibition were indistinguishable from those observed in light-reared mice. Therefore, BDNF overexpression is sufficient for the development of aspects of visual cortex in the absence of visual experience. These results suggest that reduced BDNF expression contributes to retarded maturation of GABAergic inhibition and delayed development of visual cortex during visual deprivation.

Scab caused by the fungal pathogen Venturia inaequalis is the most common disease of cultivated apple (Malus x domestica Borkh.). Monogenic resistance against scab is found in some small-fruited wild Malus species and has been used in apple breeding for scab resistance. Vf resistance of Malus floribunda 821 is the most widely used scab resistance source. Because breeding a high-quality cultivar in perennial fruit trees takes dozens of years, cloning disease resistance genes and using them in the transformation of high-quality apple varieties would be advantageous. We report the identification of a cluster of receptor-like genes with homology to the Cladosporium fulvum (Cf) resistance gene family of tomato on bacterial artificial chromosome clones derived from the Vf scab resistance locus. Three members of the cluster were sequenced completely. Similar to the Cf gene family of tomato, the deduced amino acid sequences coded by these genes contain an extracellular leucine-rich repeat domain and a transmembrane domain. The transcription of three members of the cluster was determined by reverse transcriptionpolymerase chain reaction to be constitutive, and the transcription and translation start of one member was verified by 5' rapid amplification of cDNA ends. We discuss the parallels between Cf resistance of tomato and Vf resistance of apple and the possibility that one of the members of the gene cluster is the Vf gene. Cf homologs from other regions of the apple genome also were identified and are likely to present other scab resistance genes.

Since the advent of gene manipulating techniques, it has become increasingly important to study the neural functional properties of the mouse. The bcl2 gene has a powerful inhibitory action on naturally occurring cell death. As a consequence the brain of bcl2 overexpressing mouse is 1.5 times bigger than the brain of a wild type animal and the retina has more than twice the ganglion cells than normal (Martinou, Dubois-Dauphin, Staple, Rodriguez, Frankowski, Missotten, Albertini, Talabot, Catsicas, Pietra, & Huarte (1994). Neuron, 13: 1017-1030). Since in most mammals the upper limit of behavioural visual acuity is imposed by ganglion cells density, the visual acuity should be higher in bcl2 mice than in wild type mice. We measured behavioural visual acuity in wild type and transgenic mice and, contrary to the expectation, we found it to be of the same order (0.5-0.6 c/deg) in the two groups of animals, indicating that an increase in ganglion cells density is not effective in improving visual resolution.

The basic prerequisite for an efficient breeding program to improve levels of resistance to pathogens in plants is the identification of genes controlling the resistance character. If the response to pathogens is under the control of a multilocus system, the utilization of molecular markers becomes essential. Stalk and ear rot caused by Gibberella zeae is a widespread disease of corn: resistance to G. zeae is quantitatively inherited. Our experimental approach to understanding the genetic basis of resistance to Gibberella is to estimate the genetic linkage between available molecular markers and the character, measured as the amount of diseased tissue 40 days after inoculation of a suspension of Fusarium graminearum, the conidial form of G. zeae, into the first stalk internode. Sensitive and resistant parental inbreds were crossed to obtain F1 and F2 populations: the analysis of the segregation of 95 RFLP (restriction fragment length polymorphism) clones and 10 RAPD (random amplified polymorphic DNA) markers was performed on a population of 150 F2 individuals. Analysis of resistance was performed on the F3 families obtained by selfing the F2 plants. Quantitative trait loci (QTL) detection was based either on analysis of regression coefficients between family mean value and allele values in the F2 population, or by means of interval mapping, using MAPMAKER-QTL. A linkage map of maize was obtained, in which four to five genomic regions are shown to carry factors involved in the resistance to G. zeae.