In light of these findings, we ask why do large ganglion cell types lose their antagonistic surround, and what benefit might the switch-like change in receptive field structure convey for the individual cell, as well as for the mosaic as a whole? As for the individual cell, we showed that the luminance-dependent changes in the organization of the receptive fields of two large cells (PV1 and PV6) switched DAPT purchase at a critical light level, while that of two smaller cells (PV0 and

PV2) did not. For some cells, the loss of inhibitory input would eliminate the fundamental response properties that define their function. For example, direction-selective ganglion cells are unable to discriminate direction when their inhibitory inputs are blocked (Caldwell et al., 1978; Fried et al., 2002). For small ganglion cells with center-surround receptive fields, an increase in integration area may not be a significant advantage. However, ganglion cells with large receptive field areas are well designed to detect objects when the photon count is low (low acuity, high sensitivity). For large cells, a loss of antagonistic surround would increase the area from which they could gather photons, making the cell more sensitive to photons arriving within their receptive field. Interestingly, one

type of faintly melanopsin-positive KU55933 cell, M4, has a morphology that is similar to PV1 cells (Ecker et al., 2010; Estevez et al., 2012). If the two cell types are indeed the same, an intriguing possibility is that during evolution, a class of melanopsin not cells acquired input from a special type of wide-field amacrine cell that conferred to it new spatial processing properties. The loss of antagonistic surround may also have benefits for the mosaic as a whole. The contrast sensitivity of the rod pathways is thought to be lower than that of the cone pathway. This leads to a sparser encoding of the visual scene in low light levels forming

contiguous blank neuronal representations in the rod pathways. An increased overlap between neighboring cells’ receptive fields would allow the ganglion cell mosaic to interpolate between neighboring high-contrast features (Cuntz et al., 2007; Seung and Sompolinsky, 1993). This difference in contrast sensitivity between rod and cone pathways may explain why the transition between the two circuit states is switch-like and not continuous. We found that the change in spatial integration properties of PV1 cells occurs over a small luminance change (0.07 log unit), as compared to the more than three log unit range of intensities typical of many natural scenes (Geisler, 2008; Mante et al., 2005; Rieke and Rudd, 2009). In addition, the spatial integration properties of the PV1 cell could be toggled quickly as the light level was switched above and below the threshold light level.

It is interesting that an alternative GNAT domain protein, MEC-17, was shown to acetylate tubulin in different systems, including nematodes, zebrafish, and ciliates ( Akella et al., 2010); in addition, an acetyltransferase complex, ARD1-NAT1, that can acetylate tubulin in vitro has been found associated with tubulin in developing dendrites of cultured hippocampal neurons and was shown to regulate dendritic outgrowth in vitro ( Ohkawa et al., 2008). Thus, alternative tubulin acetyltransferases that regulate

neuronal morphology have been identified. In a search of alternative cytoplasmic ELP3 selleck chemicals llc targets, we identified BRP, a large cytoskeletal-like protein that decorates the active zone where synaptic vesicles fuse with the membrane. We provide several lines of evidence that ELP3 acts to acetylate BRP at the Drosophila NMJ. First, ELP3 is present at NMJ boutons, localizing the enzyme in close proximity to BRP. Second, acetylated lysine levels that overlap with BRPNC82 labeling at the NMJ are reduced in elp3 mutants. Similarly, BRP-associated acetylated lysine levels detected by western blotting are reduced in elp3 mutants. Third, immunoprecipitated BRP is efficiently acetylated by purified ELP3 in vitro. Without excluding other substrates, our data mTOR signaling pathway indicate that ELP3 is necessary and sufficient to acetylate BRP. BRP is indeed an excellent candidate to undergo this modification as it contains numerous

coiled-coil motifs that were recently

shown to be ideal acetylation substrates ( Choudhary et al., 2009). Individual BRP strands organize into parasol-like structures, with their N termini facing the plasma membrane, contacting calcium channels, and their C termini extending into the cytoplasm capturing synaptic vesicles (Fouquet et al., 2009, Hallermann et al., 2010b and Jiao et al., 2010). While mutations that affect BRP transport to synapses or assembly of T bars at active zones exist, our data indicate that these processes are not affected in elp3 mutants. Unlike SRPK79D mutants ( Johnson et al., 2009 and Nieratschker Sclareol et al., 2009), BRPNC82 does not accumulate in elp3 mutant motor neurons (data not shown), suggesting normal axonal transport. In addition, in contrast to rab3 mutants ( Graf et al., 2009), the number of T bars per synaptic area is not different in controls and elp3 mutants. Our analyses also identified a postsynaptic role for elp3 in regulating glutamate receptor subunit IIA abundance in muscles at NMJs and, thus, mEJC amplitude; however, unlike ELP3′s neuronal function, we show that this role of ELP3 is not critical for viability, as muscular expression of the protein does not rescue elp3-associated lethality. Nonetheless, by regulating postsynaptic receptor field size, ELP3 may also modulate neuronal communication. We present evidence that this defect is regulated in muscle cells independently of the presynaptic role of ELP3.

, 1996, Perissi et al., 1999 and Yuan and Gambee, 2001). In addition, histone phosphorylation contributes to regulating gene transcription, in particular through Serine 10 phosphorylation of histone H3, which is associated with transcriptional activation. ERK MAPKs are also central to controlling histone posttranslational modifications in synaptic plasticity and experience-driven behavioral changes (Borrelli et al., 2008, Brami-Cherrier et al., 2009, Levenson et al., 2004, Reul et al., 2009 and Swank and Sweatt, 2001). Acetylation of histone H3 in the hippocampus, which is associated with long-term memory consolidation (Fischer et al., 2007, Korzus et al.,

2004, Levenson et al., 2004 and Wood et al., 2006a), is dependent on the activation of NMDA receptors and of selleck inhibitor ERK MAPK (Levenson et al., 2004). Activation of NMDA receptors and other memory- and plasticity-associated cell surface PD0332991 nmr receptors also increases acetylation of histone H3, and these effects are blocked by inhibition of ERK signaling (Brami-Cherrier et al., 2007, Brami-Cherrier et al., 2009, Levenson et al., 2004 and Reul

et al., 2009). Moreover, activation of ERK through either the PKC or PKA pathways, biochemical events known to be involved in long-term memory formation, also increases histone H3 acetylation (Brami-Cherrier et al., 2007, Brami-Cherrier et al., 2009, Levenson et al., 2004 and Reul et al., 2009). Moreover, ERK/MAPK signaling also regulates histone phosphorylation, and changes in hippocampal histone phosphorylation following fear conditioning are ERK/MAPK dependent (Chwang et al., 2006 and Wood et al., 2006b). Overall, a large body of results indicates that histone-associated

heterochromatin undergoes ERK-dependent regulation and that these histone modifications and changes in heterochromatin are necessary for hippocampal LTP and memory formation Tryptophan synthase (Alarcón et al., 2004, Korzus et al., 2004, Levenson et al., 2004 and Wood et al., 2006a). Typically, ERK does not directly affect nuclear targets, but rather acts through intermediary kinases. In a series of experiments, Chwang et al. (2007) investigated the role of mitogen- and stress-activated protein kinase 1 (MSK1), a nuclear kinase downstream of ERK, in chromatin remodeling during hippocampal-dependent memory formation. Mice lacking MSK1 showed impaired Pavlovian fear conditioning and spatial learning, as well as a deficiency in histone phosphorylation and acetylation in the hippocampus after fear training. This study identified MSK1 as an important regulator of chromatin remodeling in long-term memory, identifying a central signal transduction pathway in plasticity and memory: the ERK-MSK1-histone phosphoacetylation pathway (Figure 4). Overall, studies demonstrating a role for MAPK regulation in memory formation and in triggering lasting behavioral change are interesting in two contexts.

(2003) reported a T. gondii seroprevalence of 20.4% (82/396) in the black-eared opossums in São Paulo city, São Paulo State. In the present study, T. gondii was for the first time isolated from this species. The genotype identified from this isolate was also for the first time Regorafenib ic50 described in Brazil. Although there are already 88 genotypes identified (Su et al., 2006, Pena et al., 2008, Dubey et al., 2008, Yai et al., 2009 and Ragozo

et al., 2010) from a variety of animal hosts in Brazil, new genotypes are continuously being identified from different animal species, indicating an extremely high diversity of T. gondii in the population. This work was partially supported by Fundação de Amparo à Pesquisa EPZ 6438 do Estado de São Paulo, Brazil (FAPESP scholarship no. 2009/00175-0). S.M. Gennari is a recipient of a scholarship from Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), Brazil. “
“Filarial nematodes are major pathogens that are responsible for debilitating diseases in human populations of the tropics (‘River Blindness’, caused by Onchocerca volvulus; and lymphatic filariasis or elephantiasis, caused by Wuchereria bancrofti and Brugia spp.) and in animals (canine heartworm, caused by Dirofilaria immitis). An estimated 37 million people are infected with O. volvulus,

with a total of 90 million at risk of infection in Africa ( Anon., 2005). The adult female worms reside in subcutaneous nodules within which they must be fertilised by Isotretinoin migrating males before they can release microfilariae (Mf) into the surrounding

tissue. The Mf accumulate in the skin and eyes, and may be transferred to a female Simulium blackfly during a bloodmeal, within which they develop after two moults into infective larvae (L3). The host response to dead and dying Mf may cause immune-mediated alterations, principally severe dermatitis and visual impairment ( Enk, 2006). Control of onchocerciasis is almost exclusively dependent on annual or semi-annual mass administration of ivermectin to the affected communities (Molyneux, 2005). Ivermectin kills the Mf and thus prevents pathology, but fails to kill the adult worms, which may live for >10 years. Currently, there is no macrofilaricidal (i.e., lethal to adult worms) drug that is suitable for mass distribution. Many, but not all, filarial nematodes carry within hypodermal and other cells endosymbiotic, Rickettsia-like bacteria of the genus Wolbachia. The relatively recent rediscovery of their presence after their initial description over three decades ago ( Kozek and Marroquin, 1977) has stimulated research to exploit them as a drug target ( Hoerauf et al., 1999, Langworthy et al., 2000 and Bazzocchi et al., 2008); to investigate their possible role in aetiology of filarial disease ( Taylor et al., 2000 and Saint André et al., 2002); and to determine their functional relationship with their host worms ( Fenn and Blaxter, 2004).

, 2004). CF coactivation therefore facilitates LTD induction, and additional alterations in CF and/or PF signaling will shift the induction probabilities for LTD and LTP. Our confocal imaging studies indeed show that CF-evoked

calcium transients can be locally amplified in dendritic plasticity. Similarly, Selleckchem Navitoclax we have recently shown that repeated depolarizing current injections at 5 Hz for 3 s, one of the protocols that was also used in the present study, enhance PF-evoked spine calcium transients, and lower the probability for the subsequent induction of LTP (Belmeguenai et al., 2010). These data suggest that excitability changes in the dendrite result in altered calcium signaling and can modulate the LTD/LTP balance. In addition, our previous study (Belmeguenai et al.,

2010) showed that this form of intrinsic plasticity can be triggered by repeated current injections or PF tetanization, is measured as an increase in the number of depolarization-evoked spikes (see Figure 3) and is mediated, at least in part, by downregulation of SK channel activity (Belmeguenai et al., 2010 and Hosy et al., 2011). Thus, it is possible that intrinsic plasticity in the soma and the dendrites share an underlying Selleckchem PF01367338 cellular mechanism. Intrinsic plasticity as recorded in Purkinje cell somata depends on postsynaptic calcium transients, the activation of protein phosphatases 1, 2A, and 2B, as well as the activation of protein kinase A (PKA) and protein kinase CK2 (Belmeguenai et al., 2010). PKA and CK2 have both been shown to directly downregulate SK2 channel activity, although by distinct molecular mechanisms. While PKA regulates the surface expression of SK2 channels (Lin et al., 2008), CK2 reduces their calcium sensitivity (Allen et al., 2007 and Giessel Mephenoxalone and Sabatini, 2010). In addition to its effect on dendritic processing, dendritic plasticity alters the complex spike waveform, increasing the number of spikelets. This, in turn, could increase the number of spikes that propagate down the

axon. Previous studies have shown that the first and the last spikelets are most likely to successfully propagate, because of their relatively high amplitudes (Khaliq and Raman, 2005 and Monsivais et al., 2005). The spikelets added as a result of enhanced dendritic IE are typically seen toward the end of the waveform (see Figure 2B) and might thus be reflected in the axonal spike pattern. Therefore, changes in the complex spike waveform will not only modify the Purkinje cell interpretation of CF activity, but might also change their electrical output function, affecting the inhibition of target neurons in the cerebellar nuclei (Aizenman and Linden, 1999, Pedroarena and Schwarz, 2003 and Pugh and Raman, 2009). PF responses are modified by dendritic plasticity, depending on the position of a PF-EPSP within an EPSP train. Due to paired-pulse facilitation, the amplitude of EPSPs increases during an EPSP train.

Our analysis enabled us to study the entire time course of cortical processes underlying decision making, outcome evaluation, and learning (i.e., updating) value representations. click here Upon stimulus presentation, retrieval of learnt values activates cortical value representations

reflected in early midfrontal EEG activity. Decision certainty is reflected in P3b-like parietal EEG activity around response latency, and mapping of the selected action to the motor response is reflected in lateralized activity from (pre)motor cortices (Figure S5C). After feedback, initially outcomes are processed separately depending on whether their consequences are real or fictive, presumably in order to convert feedback information into a common value currency allowing for efficient learning of stimulus values. Then the information about necessary value updates converges on common parietal P3b-like activity modulated by whether the action was successful or not. Given the probabilistic nature of the instrumental learning task, several parameters need to be used to weight the impact of single-trial outcomes. Over the course of multiple trials, learning rate indicates the learning success and downweights the single-feedback information at later learning stages. Moreover, when a choice Selleck CP 690550 is made with high certainty, perseveration of this behavior is favorable. This means that already at the time of the response (and thus before

feedback), high certainty might be used to strengthen the current value representation, thereby shielding it from potentially misleading feedback. Interestingly, the stimulus- and feedback-locked late parietal P3b-like activity is consistent with the notion of certainty- and learning-rate-weighted value strengthening and updates at different time points: high response 3-mercaptopyruvate sulfurtransferase certainty, which should be associated with re-encoding (strengthening) of the stimulus value to assure perseveration,

is associated with high stimulus-locked P3b amplitudes. In contrast, after feedback, high learning rates and unfavorable outcomes commonly give rise to high feedback-locked P3b amplitudes, presumably reflecting value updating and storage, thereby increasing the likelihood to change future choice behavior. To put it briefly, lower stimulus-related P3b and higher feedback-related P3b amplitudes should be associated with an increased likelihood to switch choice on the next encounter with the same stimulus. This notion that feedback- and stimulus-related P3b amplitudes are inversely related to switch behavior was tested at electrode Pz, which was identified via a conjunction analysis of all relevant stimulus- and feedback-locked effects in the P3b time window (Figure 4D). A discrimination threshold was iteratively estimated in one half of randomly chosen trials that was then used to predict switching in the second half of trials.

These data strongly demonstrate that in human cells the R264Q, but not the S704C common variant, reduces Wnt signaling. Given that Wnt signaling may play a role in psychiatric disorders, we asked whether Wnt signaling was overall diminished in LCLs obtained from bipolar patients compared with healthy controls. Interestingly, when we reanalyzed our data and segregated based on case or control, we found a significant decreased in Wnt-stimulated TCF/LEF activity in bipolar patient LCLs, in a genotype-sensitive manner (Figure 5B, both panels). These data suggest

that Wnt signaling may indeed be impaired in these patients, and lithium treatment may help to increase this impairment. As a control, we ascertained whether the differences Venetoclax chemical structure in Wnt signaling

in the LCLs could be due to overall changes in the receptors for Wnt, such as the Frizzled and LRP genes. We selected a subset of Frizzled isoforms (Fzd 3, 4, and 5) and LRP6 to determine whether their expression levels differed in LCLs. We found that when comparing either RR264 versus 264QQ LCLs or control versus bipolar case LCLs, there was no significant different GDC-0449 supplier in Wnt receptor levels (Figure S3A). These data suggest that the differences in Wnt signaling in the LCLs expressing the R264Q variants is not due to changes in upstream Wnt receptor signaling. We next performed biochemical experiments using the human cell lines to determine the influence of the R264Q variant on the state of Wnt signaling. We first asked whether DISC1 R264Q regulated GSK3β activation by measuring phosphorylation of the tyrosine 216 (Y216) and the serine 9 (S9) residues. Interestingly, we found that LCLs that were homozygous for DISC1 RR264 had significantly

lower levels of phosphorylated Y216-GSK3β compared with LCLs homozygous for DISC1 264QQ (Figure 5C), suggesting GSK3β is more Chlormezanone active in LCLs homozygous for 264QQ. However, quantification of the level of serine 9 phosphorylation revealed this remained unchanged (Figure 5D). These data suggest that the R264Q variant regulates GSK3β activation by modulating phosphorylation of Y216 and indicate the reduced Wnt signaling in LCLs expressing the 264QQ variant may be due to increased activation of GSK3β. Finally, we determined whether the R264Q variant regulates the overall levels of β-catenin in human LCLs. We found that, after examining a large number of cell lines, cells expressing the RR264 variant indeed had significantly higher levels of β-catenin, consistent with their reduced activation of GSK3β and elevated Wnt signaling (Figure 5E). Last, we examined whether the DISC1 variants affected another signaling pathway in addition to Wnt signaling. We specifically focused on cyclic adenosine monophosphate (cAMP) signaling since one of the best studied functions of DISC1 is to interact with the phosphodiesterase family (PDE4B) to regulate cAMP levels (Bradshaw et al., 2011 and Millar et al., 2005).

Plasmid β-loop-TMD-Dendra2 consists of the cytoplasmic M3-M4 loop of mouse GlyRβ (residues N334–A454 excluding signal peptide, UniProt ID P48168) fused to a single transmembrane domain and extracellular Dendra2 (in analogy to βLwt-TMD-pHluorin; Specht et al., 2011). The fusion constructs were cloned in a eukaryotic expression vector derived from pEGFP-N1 (Clontech) with a partial deletion of the cytomegalovirus promoter. Spinal cord dissociated neuron cultures were prepared from Sprague-Dawley rats (at E14) and from homozygous mRFP-gephyrin KI mice (at E13) as described elsewhere (Calamai et al., 2009), in accordance with the guidelines of the French Ministry of Agriculture

and the Direction départamentale des services vétérinaires de Paris (Ecole Normale Supérieure, Animalerie des Rongeurs, license selleck B 75-05-20). Neurons were plated at a density of 6 × 104/cm2 on 18 mm coverslips (thickness, 0.13–0.16 mm); cultured in neurobasal medium containing B-27, 2 mM VEGFR inhibitor glutamine, 5 U/ml penicillin, and 5 μg/ml streptomycin at 36°C and 5% CO2; transfected with 0.5 μg plasmid DNA per coverslip using Lipofectamine 2000; and used for experiments on the following day (at 12–24 days in vitro [DIV]). COS-7 cells were grown on coverslips in Dulbecco’s modified Eagle’s medium containing 10% fetal calf serum, and cotransfected with β-loop-TMD-Dendra2 and mRFP-gephyrin in a stoichiometry of 1:4 on the day

prior to the experiments using FuGENE 6. Cell cultures were fixed for 10 min in 0.1 M sodium phosphate, pH 7.4, containing 4% paraformaldehyde (PFA) and 1% sucrose, rinsed, and imaged in PBS (pH below 7.4) (PALM and fluorophore counting). For PALM and STORM imaging, fiducial markers (TetraSpeck microspheres, 100 nm diameter, Invitrogen T7279) were attached to the coverslips after fixation. For immunolabeling, fixed neurons were permeabilized with 0.25% Triton X-100 where necessary and labeled in PBS containing 3% bovine serum albumin with antibodies against extracellular epitopes of GlyRα1 (Synaptic Systems, mAb2b, 146111, 1:200–400 dilution) and GABAARα2 (Synaptic Systems, 224103, 1:400),

the phosphorylated C domain of gephyrin (Synaptic Systems, mAb7a, 147011, 1:500; Kuhse et al., 2012), or the N terminus of bassoon (sap7f, 1:500; tom Dieck et al., 1998), followed by Alexa Fluor 647- or 488-tagged secondary antibodies (Invitrogen, 1:250–500). dSTORM was conducted in PBS (pH 7.4), containing 10% glucose, 50 mM β-mercaptoethylamine, 0.5 mg/ml glucose oxidase, and 40 μg/ml catalase, degassed with N2 (Izeddin et al., 2011). Spinal cord and cerebral cortex sections were prepared from mRFP-gephyrin KI mice. Male animals of 1 week to 6 months of age were perfused intracardially with 4% PFA and 0.1% glutaraldehyde in PBS (pH 7.4). Spinal cords (thoracic dorsal horn) and cortices (nonsuperficial layers of the frontal lobe) were dissected, postfixed with 4% PFA in PBS, cut into 1 mm segments, and incubated overnight in 2.3 M sucrose in PBS at 4°C.

R is the reversal potential of the respective conductance. Vr (−50mV) is the cell’s resting potential. The firing rate was computed as [ΔV(θ) − Vthres]n+, where Vthres, the spike threshold, was 4mV (relative to rest) and exponent n was 3 ( Priebe et al., 2004). The subscript “+” indicates rectification, i.e., that values below zero were set to zero. The tuning properties of excitatory

and inhibitory synaptic conductances (i.e., σ, gmin, gmax) in layer 2/3 Pyr cells were determined using whole-cell recordings voltage-clamp configuration where cells were held at the reversal potential for inhibition and excitation, respectively. The average visually evoked conductance was then determined for each of the six orientation of drifting gratings presented Raf inhibitor ( Figure 5C). The result was fit with a Gaussian, gX. Statistical significance was determined using the Wilcoxon sign rank, and rank sum tests where appropriate. We would like to thank C. Niell FK228 solubility dmso and M. Stryker for providing expertise and sharing code at the initial stages of this project; H. Adesnik for his help implementing optogenetic approaches; S.R. Olsen for his insights and help in developing the visual recording configuration; and J. Evora, A.N. Linder, and P. Abelkop

for histology and mouse husbandry. M.C. holds the GlaxoSmithKline / Fight for Sight Chair in Visual Neuroscience. B.V.A. was supported by NIH NS061521. This work was supported by the Gatsby Charitable Foundation and HHMI. “
“We perceive a world filled with three-dimensional (3D) objects even though 3D objects are projected onto a two-dimensional (2D) retinal image. Hence, the perception of 3D structures needs to be constructed by the brain. Yet, how and where 3D-structure perception arises from the activity of neurons within the brain remains an unanswered question. One candidate for an area that could subserve 3D-structure perception is the inferotemporal (IT) cortex. IT contains shape-selective neurons whose responses are typically tolerant to various image

transformations such as changes in size, position (in depth), or defining below cue (Ito et al., 1995, Janssen et al., 2000, Sáry et al., 1993, Schwartz et al., 1983 and Vogels, 1999). These properties make it likely that IT neurons underlie object recognition and categorization (Logothetis and Sheinberg, 1996 and Tanaka, 1996). Nonetheless, it has thus far proved difficult to unequivocally relate IT neurons having particular shape preferences to a given perceptual behavior that relies on the information encoded by those neurons. Moreover, although the representation of 3D structure is intrinsically linked to the representation of objects, the third shape dimension has hitherto received relatively little attention. The 3D structure of objects can be signaled by a variety of depth cues (Howard and Rogers, 1995).

, 2008). A pair of exciting new studies (Erskine et al. [2011] and Ruiz de Almodovar MK-8776 et al. [2011]) demonstrate for the first time that vascular endothelial growth factor (VEGF)-A released at the CNS midline functions as a chemoattractant for spinal commissural and RGC axons in vivo. Erskine et al. show that in the mammalian visual system, VEGF functions as a growth-promoting factor

that promotes extension of contralaterally projecting RGC axons across the midline, while Ruiz de Almodovar et al. find that in the spinal cord, VEGF secreted from the floor plate is an attractant for precrossing spinal commissural axons. VEGF is best known for its proangiogenic function during blood vessel growth in vivo, and recent studies have revealed that VEGF also promotes neural progenitor proliferation, survival, migration, and differentiation (Greenberg and Jin, 2005). However, these present studies selleck products demonstrate the versatility of VEGF-A, expanding its repertoire to include chemoattractant function essential for proper nervous system wiring. In their search for guidance cues that function as chemoattractants at the mammalian optic chiasm, Erskine and colleagues initially observe that mice lacking Neuropilin-1 (Npn-1), a transmembrane receptor for class 3 Semaphorins and

select isoforms of VEGF-A ( Adams and Eichmann, 2010), display increased ipsilateral projections at the optic chiasm at embryonic day (E)14.5 in vivo. No defects at the chiasm were observed in mice deficient for the related Neuropilin-2 receptor. Despite the early lethality of Npn-1 germline null mice, the chiasm appears to develop normally, and no changes in expression of EphrinB2 or Slits were observed. Furthermore, the ventrotemporal domain of the retina that gives rise to most only ipsilateral RGC projections is not enlarged in Npn-1 mutants. When coupled with the strong expression

of Npn-1 on contralaterally projecting RGC axons, this phenotype suggested a role for Npn-1 in promoting RGC axon midline crossing. Interestingly, expression of class 3 Semaphorin family members (Sema3s) at the chiasm is not observed, or is extremely low, at the time when RGCs cross. To rule out potential influences from more remote Sema3 sources, mice carrying a Npn-1 point mutation that abolishes Sema3, but not VEGF, signaling (Npn1Sema−/−) ( Gu et al., 2003) were analyzed. Similar to wild-type mice, Npn1Sema−/− mice show no midline crossing defects at the optic chiasm. With a vital role for Sema3s eliminated, Erskine et al. (2011) turned their attention to isoforms of VEGF-A, a second class of Npn-1 ligands. VEGF-A is strongly expressed at the embryonic optic chiasm in the mouse.