Overlapping functions of the cell adhesion molecules Nr-CAM and L1 in cerebellar granule cell development

The structurally related cell adhesion molecules L1 and Nr-CAM have overlapping expression patterns in cerebellar granule cells. Here we analyzed their involvement in granule cell development using mutant mice. Nr-CAM–deficient cerebellar granule cells failed to extend neurites in vitro on contactin, a known ligand for Nr-CAM expressed in the cerebellum, confirming that these mice are functionally null for Nr-CAM. In vivo, Nr-CAM–null cerebella did not exhibit obvious histological defects, although a mild size reduction of several lobes was observed, most notably lobes IV and V in the vermis. Mice deficient for both L1 and Nr-CAM exhibited severe cerebellar folial defects and a reduction in the thickness of the inner granule cell layer. Additionally, anti-L1 antibodies specifically disrupted survival and maintenance of Nr-CAM–deficient granule cells in cerebellar cultures treated with antibodies. The combined results indicate that Nr-CAM and L1 play a role in cerebellar granule cell development, and suggest that closely related molecules in the L1 family have overlapping functions

A Forward Genetic Screen in Mice Identifies Mutants with Abnormal Cortical Patterning

Formation of a 6-layered cortical plate and axon tract patterning are key features of cerebral cortex development. Abnormalities of these processes may be the underlying cause for a range of functional disabilities seen in human neurodevelopmental disorders. To identify mouse mutants with defects in cortical lamination or corticofugal axon guidance, N-ethyl-N-nitrosourea (ENU) mutagenesis was performed using mice expressing LacZ reporter genes in layers II/III and V of the cortex (Rgs4-lacZ) or in corticofugal axons (TAG1-tau-lacZ). Four lines with abnormal cortical lamination have been identified. One of these was a splice site mutation in reelin (Reln) that results in a premature stop codon and the truncation of the C-terminal region (CTR) domain of reelin. Interestingly, this novel allele of Reln did not display cerebellar malformation or ataxia, and this is the first report of a Reln mutant without a cerebellar defect. Four lines with abnormal cortical axon development were also identified, one of which was found by whole-genome resequencing to carry a mutation in Lrp2. These findings demonstrated that the application of ENU mutagenesis to mice carrying transgenic reporters marking cortical anatomy is a sensitive and specific method to identify mutations that disrupt patterning of the developing brain

The Economic Impact of Eradicating Peste des Petits Ruminants:A Benefit-Cost Analysis

Peste des petits ruminants (PPR) is an important cause of mortality and production loss among sheep and goats in the developing world. Despite control efforts in a number of countries, it has continued to spread across Africa and Asia, placing an increasing burden on the livelihoods of livestock keepers and on veterinary resources in affected countries. Given the similarities between PPR and rinderpest, and the lessons learned from the successful global eradication of rinderpest, the eradication of PPR seems appealing, both eliminating an important disease and improving the livelihoods of the poor in developing countries. We conducted a benefit-cost analysis to examine the conomic returns from a proposed programme for the global eradication of PPR. Based on our knowledge and experience, we developed the eradication strategy and estimated its costs. The benefits of the programme were determined from (i) the averted mortality costs, based on an analysis of the literature, (ii) the downstream impact of reduced mortality using a social accounting matrix, and (iii) the avoided control costs based on current levels of vaccination. The results of the benefit-cost analysis suggest strong economic returns from PPR eradication. Based on a 15-year programme with total discounted costs of US$2.26 billion, we estimate discounted benefits of US$76.5 billion, yielding a net benefit of US$74.2 billion. This suggests a benefit cost ratio of 33.8, and an internal rate of return (IRR) of 199%. As PPR mortality rates are highly variable in different populations, we conducted a sensitivity analysis based on lower and higher mortality scenarios. All the scenarios examined indicate that investment in PPR eradication would be highly beneficial economically. Furthermore, removing one of the major constraints to small ruminant production would be of considerable benefit to many of the most vulnerable communities in Africa and Asia

Distinct Cis Regulatory Elements Govern the Expression of TAG1 in Embryonic Sensory Ganglia and Spinal Cord

Cell fate commitment of spinal progenitor neurons is initiated by long-range, midline-derived, morphogens that regulate an array of transcription factors that, in turn, act sequentially or in parallel to control neuronal differentiation. Included among these are transcription factors that regulate the expression of receptors for guidance cues, thereby determining axonal trajectories. The Ig/FNIII superfamily molecules TAG1/Axonin1/CNTN2 (TAG1) and Neurofascin (Nfasc) are co-expressed in numerous neuronal cell types in the CNS and PNS – for example motor, DRG and interneurons - both promote neurite outgrowth and both are required for the architecture and function of nodes of Ranvier. The genes encoding TAG1 and Nfasc are adjacent in the genome, an arrangement which is evolutionarily conserved. To study the transcriptional network that governs TAG1 and Nfasc expression in spinal motor and commissural neurons, we set out to identify cis elements that regulate their expression. Two evolutionarily conserved DNA modules, one located between the Nfasc and TAG1 genes and the second directly 59 to the first exon and encompassing the first intron of TAG1, were identified that direct complementary expression to the CNS and PNS, respectively, of the embryonic hindbrain and spinal cord. Sequential deletions and point mutations of the CNS enhancer element revealed a 130bp element containing three conserved E-boxes required for motor neuron expression. In combination, these two elements appear to recapitulate a major part of the pattern of TAG1 expression in the embryonic nervous system

The chick cE enhancer drives expression in motor neurons.

<p>A. The genomic organization of the region between the chick <i>Nfasc</i> and <i>TAG1</i> genes. The red box represents the cE element. B,C. The cE enhancer was cloned upstream to Gal4 transactivator and electroporated at HH18 into the chick neural tube along with UAS-GFP plasmid. GFP is expressed in motor neurons and roof plate cells. B. Co-staining with Isl1 antibody reveals that the ventral GFP expressing neurons express the motor neurons transcription factor Isl1. C. Co-staining with TAG1/Axonin-1 antibody demonstrates that the differentiated motor neurons, reside in the lateral ventral spinal cord, express GFP and TAG1. D. Schematic representation of the plasmids used in B and C. The cE3 enhancer was cloned up stream to Gal4 and co-elecroporated with UAS::GFP plasmid. Scale Bar B–C 50 µm.</p

E3 enhancer directs expression in dI1 neurons.

<p>E3::Cre and CAG-STOP^LoxP-nGFP were co-electroporated. Cross sections of HH26 spinal cord were stained with cell fate markers. In the dorsal spinal cord, most of the nGFP cells express the dI1 cell fate marker Lhx2/9 (A) and Brn3a (yellow arrows in B). Few cells express the dI2 markers Brn3a+Lhx1 (white arrows in B). dI3 (Isl1+) and dI4-6 (Lhx1+/Brn3a-) do not express nGFP (A,B). Co expression of GFP driven by dI1 specific enhancer <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0057960#pone.0057960-Avraham2" target="_blank">[10]</a>, and mCherry driven by E3 enhancer (D), demonstrate overlapping expression in the dorsal interneurons (C). Scale Bar A-B 50 µm, C100 µm.</p

Quantification of GFP labeled neurons.

<p>Cross sections of HH24 electroporated embryos were stained with cell fate markers. Interneurons (IN) were stained with Lhx2/9, Lhx1, Isl1, Brn3a and motor neurons (MN) with Isl1. Progenitor cells that reside in the ventricular zone, that do not express any of the cell fate markers, were classified according to their dorsoventral location. Roof plate cells (RF) were defined as dorsal midline cells that do not express the dI1-3 cell fate marker Brn3a.</p

Expression pattern of TAG1, Nfasc and the E3 enhancer in the chick embryonic spinal cord.

<p>The neural tube of HH st. 18 chick embryos were electroporated with E3::Cre + CAG-STOP^LoxP-GFP plasmids. Cross sections of HH24 (A–D), HH26 (E–H) and HH28 ( I–L) were stained for TAG1 (A,E,I), Nfasc (B,F,J) and GFP (C,G,K). The merged triple staining is shown in D,H,L. White arrows point to commissural axons. White arrowheads point to motor axons. Yellow arrows point to DRG axons. Green arrows point to ipsilaterally projecting axons. Scale Bar A–D 70 µm, E-H 90 µm, I-L 140 µm.</p

Functional dissection of the E3 enhancer element.

<p>A. A scheme showing the mouse genomic organization of the region between the 3′ of <i>Nfasc</i> and 5′ of <i>TAG1</i>. B. A zoom-in of the E3 element showing the E3.1 and E3.3 elements. C. Alignment of the mouse E3 element to the human, orangutan, dog, horse and Opossum elements. The Alignment was done using BLAT alignment tool of UCSC genome bioinformatics (<a href="http://genome.ucsc.edu/cgi-bin/hgGateway" target="_blank">http://genome.ucsc.edu/cgi-bin/hgGateway</a>). D–G. The expression patterns of GFP driven by the indicated enhancer (at the bottom right side of each image) at HH26 chick spinal cord. Each enhancer was cloned upstream to Cre recombinase and electroporated at HH18 into the chick neural tube along with CAG-STOP^LoxP-GFP plasmid. H,I. The expression pattern of E3.1::LacZ in E11.5 mouse embryo. The boxed area in H is shown as a magnification in H’. Arrows point to dorsal neurons and commissural axons. Arrowheads point to motor neurons and motor axons. Scale Bar A–G 50 µm, H-75 µm, H'-25 µm.</p