Mouse Forelimb Research Articles

A Tick Cysteine Protease Inhibitor RHcyst-1 Exhibits Antitumor Potential

Background/Aims: We previously identified a potent and tight-binding inhibitor of cysteine proteases from Rhipicephalus haemaphysaloides, RHcyst-1, which belongs to the cystatin type 1 family. Cathepsins, which are members of the cysteine protease family, participate in various pathological processes, including the initiation and development of cancers. The present study aimed to investigate the antitumor effects of RHcyst-1 and to explore the underlying mechanism of these effects. Methods: Different tumor cells were treated with RHcyst-1 in vitro. Proliferation activity was evaluated using Cell Counting Kit-8, and migration and invasion were determined by wound healing and Transwell® invasion assays. In addition, a mouse tumor therapy model was established by inoculating the left forelimb of mice with B16-F10 cells, and tumor progression was evaluated by assessing tumor volume and survival. Flow cytometry was conducted to evaluate myeloid-derived suppressor cells (MDSCs), CD4⁺, and CD8⁺ T cell levels in PBMCs and spleens. Immunohistochemistry was performed to analyze immune cell infiltration and angiogenesis in the tumors. Results: RHcyst-1 significantly inhibited the proliferation, migration, and invasion of all four different tumor cells in vitro. Additionally, it inhibited tumor growth and improved survival in vivo. A decrease and an increase in MDSCs levels were observed in PBMCs and in the spleen, respectively, after RHcyst-1 application. Conclusions: Tick RHcyst-1 has potential antitumor efficacy, and the observed antitumor activities may be partly attributable to changes in cathepsin expression and MDSCs levels in the PBMCs and spleens. The findings of the present study suggest that RHcyst-1 may have the potential to be utilized in cancer treatment.

Combining robotic training and inactivation of the healthy hemisphere restores pre-stroke motor patterns in mice.

Focal cortical stroke often leads to persistent motor deficits, prompting the need for more effective interventions. The efficacy of rehabilitation can be increased by 'plasticity-stimulating' treatments that enhance experience-dependent modifications in spared areas. Transcallosal pathways represent a promising therapeutic target, but their role in post-stroke recovery remains controversial. Here, we demonstrate that the contralesional cortex exerts an enhanced interhemispheric inhibition over the perilesional tissue after focal cortical stroke in mouse forelimb motor cortex. Accordingly, we designed a rehabilitation protocol combining intensive, repeatable exercises on a robotic platform with reversible inactivation of the contralesional cortex. This treatment promoted recovery in general motor tests and in manual dexterity with remarkable restoration of pre-lesion movement patterns, evaluated by kinematic analysis. Recovery was accompanied by a reduction of transcallosal inhibition and 'plasticity brakes' over the perilesional tissue. Our data support the use of combinatorial clinical therapies exploiting robotic devices and modulation of interhemispheric connectivity.

Osteogenic Potential of Caspases Related to Endochondral Ossification.

Caspases have functions particularly in apoptosis and inflammation. Increasing evidence indicates novel roles of these proteases in cell differentiation, including those involved in osteogenesis. This investigation provides a complex screening of osteogenic markers affected by pan caspase inhibition in micromass cultures derived from mouse forelimbs. PCR Array analysis showed significant alterations in expression of 49 osteogenic genes after 7 days of inhibition. The largest change was a decrease in CD36 expression, which was confirmed at organ level by caspase inhibition in cultured mouse ulnae followed by CD36 immunohistochemical analysis. So far, available data point to osteogenic potential of pro-apoptotic caspases. Therefore, the expression of pro-apoptotic caspases (-3, -6, -7, -8, -9) within the growth plate of mouse forelimbs at the stage where the individual zones are clearly apparent was studied. Caspase-9 was reported in the growth plate for the first time as well as caspase-6 and -7 in the resting zone, caspase-7 in the proliferation, and caspase-6 and -8 in the ossification zone. For all caspases, there was a gradient increase in activation toward the ossification zone. The distribution of staining varied significantly from that of apoptotic cells, and thus, the results further support non-apoptotic participation of caspases in osteogenesis.

MRI reveals slow clearance of dead cell transplants in mouse forelimb muscles.

A small molecule tetraazacyclododecane-1,4,7,10-tetraacetic acid (Gd-DOTA)4-TPP agent is used to label human mesenchymal stem cells (hMSCs) via electroporation (EP). The present study assessed the cytotoxicity of cell labeling, in addition to its effect on cell differentiation potential. There were no significant adverse effects on cell viability or differentiation induced by either EP or cellular uptake of (Gd-DOTA)4-TPP. Labeled live and dead hMSCs were transplanted into mouse forelimb muscles. T2-weighted magnetic resonance imaging (MRI) was used to track the in vivo fate of the cell transplants. The labeling and imaging strategy allowed long term tracking of the cell transplants and unambiguous distinguishing of the cell transplants from their surrounding tissues. Cell migration was observed for live hMSCs injected into subcutaneous tissues, however not for either live or dead hMSCS injected into limb muscles. A slow clearance process occurred of the dead cell transplants in the limb muscular tissue. The MRI results therefore reveal that the fate and physiological activities of cell transplants depend on the nature of their host tissue.

Pitx1 determines characteristic hindlimb morphologies in cartilage micromass culture.

The shapes of homologous skeletal elements in the vertebrate forelimb and hindlimb are distinct, with each element exquisitely adapted to their divergent functions. Many of the signals and signalling pathways responsible for patterning the developing limb bud are common to both forelimb and hindlimb. How disparate morphologies are generated from common signalling inputs during limb development remains poorly understood. We show that, similar to what has been shown in the chick, characteristic differences in mouse forelimb and hindlimb cartilage morphology are maintained when chondrogenesis proceeds in vitro away from the endogenous limb bud environment. Chondrogenic nodules that form in high-density micromass cultures derived from forelimb and hindlimb buds are consistently different in size and shape. We described analytical tools we have developed to quantify these differences in nodule morphology and demonstrate that characteristic hindlimb nodule morphology is lost in the absence of the hindlimb-restricted limb modifier gene Pitx1. Furthermore, we show that ectopic expression of Pitx1 in the forelimb is sufficient to generate nodule patterns characteristic of the hindlimb. We also demonstrate that hindlimb cells are less adhesive to the tissue culture substrate and, within the limb environment, to the extracellular matrix and to each other. These results reveal autonomously programmed differences in forelimb and hindlimb cartilage precursors of the limb skeleton are controlled, at least in part, by Pitx1 and suggest this has an important role in generating distinct limb-type morphologies. Our results demonstrate that the micromass culture system is ideally suited to study cues governing morphogenesis of limb skeletal elements in a simple and experimentally tractable in vitro system that reflects in vivo potential.

Parvalbumin-Expressing GABAergic Neurons in Primary Motor Cortex Signal Reaching

SummaryThe control of targeted reaching is thought to be shaped by distinct subtypes of local GABAergic inhibitory neurons in primary forelimb motor cortex (M1). However, little is known about their action potential firing dynamics during reaching. To address this, we recorded the activity of parvalbumin-expressing (PV+) GABAergic neurons identified from a larger population of fast-spiking units and putative excitatory regular-spiking units in layer 5 of the mouse forelimb M1 during an M1-dependent, sensory-triggered reaching task. PV+ neurons showed short latency responses to the acoustic cue and vibrotactile trigger stimulus and an increase in firing at reaching onset that scaled with the amplitude of reaching. Unexpectedly, PV+ neurons fired before regular-spiking units at reach onset and showed high overall firing rates during both sensory-triggered and spontaneous reaches. Our data suggest that increasing M1 PV+ neuron firing rates may play a role in the initiation of voluntary reaching.

Abstract P14: A Novel Forelimb Orthotopic Allotransplantation Model in Mouse

PURPOSE: In translational research related to Vascularized composite allotransplantation (VCA), mouse models provide a profoundly relevant means to successfully studying of crucial aspects related to the immunobiology of graft rejection and acceptance, neuronal reinnervation of sensory and motor function and associated cortical reintegration of lost extremity function. The model developed here is designed to address this critical void to allow for mouse orthotopic forelimb transplantation, a tool to studying both aspects of functional recovery and immunobiology related to VCA in a genetically versatile mouse model system. METHODS: Male Balb/c donors and C57BL/6 recipients (8–10 weeks) mice were used to perform syngeneic and allogeneic orthotopic forelimb transplantation. Co-stimulation blockaded (CTLA4-Ig & MR-1) was used for immunosuppression. A circumferential skin incision was made at the shoulder. The pectoralis major muscle insertion was released at the humerus and reflected. The vascular pedicle was dissected from the axilla to the cubital fossa and transected at the level of the proximal axillary artery. Median and ulnar nerves were identified and transected proximal to the cubital fossa. The radial nerve was identified and transected dorsally at the intersection of medial and distal third of the humerus. Both flexor and extensor muscle groups were cauterized and transected at mid humerus level. In the recipient animal shoulder mobility was preserved and vessels and nerves were transected proximal to the cubital fossa. The graft was secured by muscle approximation with 6-0 Polysorb and by using a 26G spinal needle as an intramedullary rod for osteosynthesis. A non-suture cuff technique was employed to anastomose donor axillary vessels with recipient brachial (mid-arm) vessels. Tension free primary end-to-end neurorrhaphy was performed in median, ulnar and radial nerves using 11-0 microsuture. RESULTS: Long term animal and graft survival in syngeneic transplant combinations demonstrated the feasibility of orthotopic mouse forelimb transplantation with only limited behavioral disabilities (>60 days; N=3).The non-suture cuff technique allows for successful supermicrovascular anastomosis of the donor axillary vessel with the recipient brachial vessel. The feasibility of radial, median and ulnar nerve coaptation provides the basis for studying functional recovery as well as cortical reintegration of upper extremity function after VCA. Long term allograft survival (>4 months; N=3) underpins the applicability of orthotopic forelimb transplantation for studying the immunobiology of functional extremity reconstruction using VCA. CONCLUSION: The described orthotopic forelimb transplantation model in the mouse is designed to add an additional research model for VCA by providing the option of using the entire range of genetically engineered mice for research related to transplant immunology, neuroregeneration, and functional recovery after upper extremity transplantation.

Hox gene expression in the specialized limbs of the Iberian mole (Talpa occidentalis).

Fossorial talpid moles use their limbs predominantly for digging, which explains their highly specialized anatomy. The humerus is particularly short and dorsoventrally rotated, with broadened distal and proximal parts where muscles attach and which facilitate powerful abductive movements. The radius and ulna are exceptionally robust and short. The ulna has an expanded olecranon process. The femur is generalized, but the fused tibia-fibula complex is short and robust. To understand the developmental bases of these specializations, we studied expression patterns of four 5' Hox genes in the fossorial Iberian mole (Talpa occidentalis). These genes are known to play major roles in patterning the developing limb skeleton in the mouse, with which comparisons were made (Mus musculus, C57BL/6Jico strain). We find that HoxA9 expression is spatially expanded in the developing stylopodial area in the mole forelimb, compared to the less specialized mouse forelimb and mole hind limb. HoxD9 expression does not extend into the thoracic body wall in the mole forelimb in contrast to the mouse, and is also reduced in the presumptive zeugopodium in mole forelimb, compared to mouse. Expression of HoxD11 is upregulated in the mole in the postaxial area of the hind limb zeugopod, compared to the mouse. On the other hand, HoxD13 is downregulated in the postaxial zeugopodial area in the forelimb of the mole, compared to the mouse. The differences in the expression patterns of these 5' Hox genes between Talpa and Mus are an indication of the developmental changes going hand in hand with anatomical digging adaptations in the mole adult.

Establishment of Human Chronic Lymphocytic Leukemia Model in the BALB/c Nude Mice by Using MEC-1 and HG3 Cell Lines

To explore the the optimal condition for establishing immune deficiency mouse(BALB/c) model with CLL via subcutaneous inoculation of human chronic lymphocytic leukemia (CLL) cells at different inoculative locations and different cell concentrations. Firstly, Two CLL cell lines (MEC-1-GFP and HG3-GFP)with the green fluorescent protein (GFP) were established by lentivirus system respectively, and then the MEC-1-GFP cells (5×107/ml) were inoculated into forelimb, hindlimb and abdomen to observe the tumorigenesis. Secondly, the MEC-1-GFP and HG3-GFP cells with same density (5×107/ml) were inoculated into forelimb to compare the time and rate of tumor formation. Thirdly, the MEC-1-GFP cells (1×107/ml) and HG3-GFP cells (5×107/ml) were inoculated into forelimb to compare the time and rate of tumor formation at different inoculative density. After observation for 5 weeks, the peripheral blood was collected and treated with EDTA and erythrocytolysin, then the of GFP positive cells were detected by flow cytomety. Meanwhile, the tumor-bearing mice were killed, and the tumors were isolated and cut into slices for histopathological examination. MEC-1-GFP and HG3-GFP cell lines were successfully established, and after inocutation of MEC-1-GFP cells with 5×107/ml the xenograt tumors were formated in forelimb, hindlimb and abdomen of mice, especially in the forelimb with a higher tumorigenic rate. In addition, the inoculation of same density of MEC-1-GFP and HG3-GFP cells (5×107/ml) also resulted in xenograft in forelimb, and the tumorigenic rate reached to 80% after 5 weeks. Moreover, the inocutation of MEC-1-GFP and HG3-GFP cells with 1×107 and 5×107/ml respectively also effectively resulted to xenograft tumor in forelimb. The flow cytometry showed that there was no MEC-1-GFP and HG3-GFP cells in peripheral blood, while histopathological examination demonstrated CLL cell metastasis towards peritoneal cavity. The BALB/c nude mouse model is successfully established by subcutaneous injection of MEC-1-GFP and HG3-GFP cells. This model is a useful tool to explore the pathogenic mechanism.

Reducing GABAA-mediated inhibition improves forelimb motor function after focal cortical stroke in mice.

A deeper understanding of post-stroke plasticity is critical to devise more effective pharmacological and rehabilitative treatments. The GABAergic system is one of the key modulators of neuronal plasticity, and plays an important role in the control of “critical periods” during brain development. Here, we report a key role for GABAergic inhibition in functional restoration following ischemia in the adult mouse forelimb motor cortex. After stroke, the majority of cortical sites in peri-infarct areas evoked simultaneous movements of forelimb, hindlimb and tail, consistent with a loss of inhibitory signalling. Accordingly, we found a delayed decrease in several GABAergic markers that accompanied cortical reorganization. To test whether reductions in GABAergic signalling were causally involved in motor improvements, we treated animals during an early post-stroke period with a benzodiazepine inverse agonist, which impairs GABAA receptor function. We found that hampering GABAA signalling led to significant restoration of function in general motor tests (i.e., gridwalk and pellet reaching tasks), with no significant impact on the kinematics of reaching movements. Improvements were persistent as they remained detectable about three weeks after treatment. These data demonstrate a key role for GABAergic inhibition in limiting motor improvements after cortical stroke.

Expression of Fas, FasL, caspase-8 and other factors of the extrinsic apoptotic pathway during the onset of interdigital tissue elimination.

Elimination of the interdigital web is considered to be the classical model for assessing apoptosis. So far, most of the molecules described in the process have been connected to the intrinsic (mitochondrial) pathway. The extrinsic (receptor mediated) apoptotic pathway has been rather neglected, although it is important in development, immunomodulation and cancer therapy. This work aimed to investigate factors of the extrinsic apoptotic machinery during interdigital regression with a focus on three crucial initiators: Fas, Fas ligand and caspase-8. Immunofluorescent analysis of mouse forelimb histological sections revealed abundant expression of these molecules prior to digit separation. Subsequent PCR Array analyses indicated the expression of several markers engaged in the extrinsic pathway. Between embryonic days 11 and 13, statistically significant increases in the expression of Fas and caspase-8 were observed, along with other molecules involved in the extrinsic apoptotic pathway such as Dapk1, Traf3, Tnsf12, Tnfrsf1A and Ripk1. These results demonstrate for the first time the presence of extrinsic apoptotic components in mouse limb development and indicate novel candidates in the molecular network accompanying the regression of interdigital tissue during digitalisation.

Micro PET imaging of 18F-Fluoromisonidazole in an MDA-MB-231 triple negative human breast cancer xenograft model

Background: While 18 F-Fluoromisonidazole ( 18 F-FMISO) is the most frequently used positron emission tomography (PET) tracer for detecting hypoxia, it has not been studied in a metastatic triple-negative [lack expression of estrogen receptor (ER), progesterone receptor (PR) and human EGF receptor 2 (HER2)] human breast cancer cell xenografts model to our best knowledge. This study focuses on whether 18 F-FMISO can detect the hypoxic status of triple-negative human breast cancer (TNBC). Methods: The TNBC cells MDA-MB-231 were successfully inoculated in right forelimb of nude mice. Nude mice models with TNBC xenografts were assessed by micro-PET imaging with 18 F-FMISO, and hypoxic status of the TNBC xenografts was determined by immunohistochemistry. We also compared 18 F-FDG uptake, the most commonly used PET tracer in clinical practice, with 18 F-FMISO uptake to find out its correlation in MDA-MB-231 xenografts. Results: For 18 F-FMISO, intestines and liver as well as bladder could be seen in micro-PET images. 18 F-FDG showed physiologically high uptake in brain, heart, bladder and intestinal tracts. The quantitative radioactivity of 18 F-FMISO and 18 F-FDG in tumor were 2.18±0.15 and 3.84±0.54 %ID/g, respectively. The quantitative radioactivity of 18 F-FMISO and 18 F-FDG in muscle were 1.23±0.08 and 0.59±0.09 %ID/g, respectively. The tumor-to-muscle ratios were 1.79±0.015 and 7.11±2.84 for 18 F-FMISO and 18 F-FDG, respectively. Immunofluorescent images from MDA-MB-231 cryosections showed significant hypoxia. Conclusions: 18 F-FMISO PET may be used for detection of hypoxia in tumor microenvironment of triple negative human breast cancer.

Mapping the chromatin state dynamics in myoblasts

BackgroundGenome-wide mapping reveals chromatin landscapes unique to cell states. Histone marks of regulatory genes involved in cell specification and organ development provide a powerful tool to map regulatory sequences. H3K4me3 marks promoter regions; H3K27me3 marks repressed regions, and Pol II presence indicates active transcription. The presence of both H3K4me3 and H3K27me3 characterize poised sequences, a common characteristic of genes involved in pattern formation during organogenesis. ResultsWe used genome-wide profiling for H3K27me3, H3K4me3, and Pol II to map chromatin states in mouse embryonic day 12 forelimbs in wild type (control) and Pitx2-null mutant mice. We compared these data with previous gene expression studies from forelimb Lbx1+ migratory myoblasts and correlated Pitx2-dependent expression profiles and chromatin states. During forelimb development, several lineages including myoblast, osteoblast, neurons, angioblasts, etc., require synchronized growth to form a functional limb. We identified 125 genes in the developing forelimb that are Pitx2-dependent. Genes involved in muscle specification and cytoskeleton architecture were positively regulated, while genes involved in axonal path finding were poised. ConclusionOur results have established histone modification profiles as a useful tool for identifying gene regulatory states in muscle development, and identified the role of Pitx2 in extending the time of myoblast progression, promoting formation of sarcomeric structures, and suppressing attachment of neuronal axons.

Caspases and osteogenic markers--in vitro screening of inhibition impact.

Caspases, well-known players in apoptosis or inflammation, appear to have roles also in other processes such as cell differentiation. Caspase-3, in particular, was recently demonstrated to have non-apoptotic functions in osteogenesis. However, the molecular pathways involved are not yet known. Therefore, we used osteogenic PCR arrays to provide a comprehensive screening of possible interactions of caspases in general and specifically of caspase-3 in osteogenic networks. Embryonic micromass cultures derived from mouse forelimbs were established and pharmacological fluoromethylketone (FMK) inhibitors applied. Alterations were observed in expression of several genes after caspase inhibition (Bmp1, Bmp5, Bmp6, Col10a1, Col2a1, Comp, Egf, Fgfr2, Gli1, Igf1, Nog, Phex, Sox9, Spp1). The list suggests molecular interactions of caspases and osteogenic molecules and creates a background for further temporospatial and functional studies.

An automated task for the training and assessment of distal forelimb function in a mouse model of ischemic stroke

BackgroundBehavioral models relevant to stroke research seek to capture important aspects of motor skills typically impaired in human patients, such as coordination of distal musculature. Such models may focus on mice since many genetic tools are available for use only in that species and since the training and behavioral demands of mice can differ from rats even for superficially similar behavioral readouts. However, current mouse assays are time consuming to train and score, especially in a manner producing continuous quantification. An automated assay of mouse forelimb function may provide advantages for quantification and speed, and may be useful for many applications including stroke research. New methodWe present an automated assay of distal forelimb function. In this task, mice reach forward, grip and pull an isometric handle with a prescribed force. The apparatus partially automates the training process so that mice can be trained quickly and simultaneously. ResultsUsing this apparatus, it is possible to measure long-lasting impairment in success rate, force pulled, latency to pull, and latency to success up to 22 weeks following photothrombotic cortical strokes in mice. Comparison with existing method(s)This assessment measures forelimb function as do pellet reach tasks, but it utilizes a different motion and provides automatic measures that can ease and augment the research process. ConclusionsThis high-throughput behavioral assay can detect long-lasting motor impairments, eliminates the need for subjective scoring, and produces a rich, continuous data set from which many aspects of the reach and grasp motion can be automatically extracted.

Segmental distribution of the motor neuron columns that supply the rat hindlimb: A muscle/motor neuron tract-tracing analysis targeting the motor end plates

Spinal cord injury (SCI) that disrupts input from higher brain centers to the lumbar region of the spinal cord results in paraplegia, one of the most debilitating conditions affecting locomotion. Non-human primates have long been considered to be the most appropriate animal to model lower limb dysfunction. More recently, however, there has been a wealth of scientific information gathered in the rat regarding the central control of locomotion. Moreover, rodent models of SCI at lumbar levels have been widely used to validate therapeutic scenarios aimed at the restoration of locomotor activities. Despite the growing use of the rat as a model of locomotor dysfunction, knowledge regarding the anatomical relationship between spinal cord motor neurons and the hindlimb muscles that they innervate is incomplete. Previous studies performed in our laboratory have shown the details of the muscle/motor neuron topographical relationship for the mouse forelimb and hindlimb as well as for the rat forelimb. The present analysis aims to characterize the segmental distribution of the motor neuron pools that innervate the muscles of the rat hindlimb, hence completing this series of studies. The location of the motor end plate (MEP) regions on the main muscles of the rat hindlimb was first revealed with acetylcholinesterase histochemistry. For each muscle under scrutiny, injections of Fluoro-Gold were then performed along the length of the MEP region. Targeting the MEPs gave rise to columns of motor neurons that span more spinal cord segments than previously reported. The importance of this study is discussed in terms of its application to gene therapy for SCI.

Expression Pattern of the Orphan Nuclear Receptor, Nurr1, in the Developing Mouse Forelimb and its Relationship to Limb Skeletogenesis and Osteogenesis

The NR4A orphan nuclear receptor, Nurr1, has been shown to regulate the expression of osteoblastic genes and osteoblastic differentiation. However, the expression profile of Nurr1 in the developing mouse forelimb and its relationship to skeletogenesis has not, to the best of our knowledge, been previously analyzed. In this study, the relationship between Nurr1 expression pattern, skeletogenesis and osteogenesis in the developing mouse forelimb was investigated. The expression level of Nurr1 during development was also quantified by real time-polymerase chain reaction. Our results revealed that Nurr1 is expressed in the mesenchyme cells that will form the skeleton. Nurr1 is aabundantly expressed in the primary ossification centers of the forelimb skeletal elements and its expression level is gradually increased during limb development, particularly, at the onset of ossification. Collectively, these data suggested that Nurr1 plays an important role in skeletogenesis and patterning of the developing mouse forelimb.

Arm and hand movement: current knowledge and future perspective.

Reaching with the arm and grasping with the hand and fingers is a complex behavior that appears in utero, is elaborated over the first few years of life, and serves useful everyday functions throughout the course of human life. Several neurological conditions can impair the ability to produce arm and hand movements and so greatly impact on the quality of life and well-being of the affected individuals. Given the fundamental role that arm and hand movements play in everyday life, deficits related to arm and hand function are one of the most debilitating motor conditions. Neurological conditions that can affect arm and hand movements include autism spectrum disorder, Parkinson’s and Huntington’s diseases, amyotrophic lateral sclerosis, cerebral palsy, and stroke-related motor cortex damage as well as spinal cord injury at cervical levels. While arm and hand movement has received considerable attention from both clinicians and researchers from diverse scientific backgrounds, there are a number of broad research questions that still need to be addressed in this research field. The present Research Topic is entirely devoted to arm and hand movement in health as well as in disease. It is a compilation of original research papers and reviews, clinical case studies, hypothesis and theory articles, opinions, commentaries, and methods articles that cover important aspects of the topic from different perspectives. In this volume, de Bruin et al. (1) present data that describe how healthy adults use space while performing a visually guided grasping task. A model for understanding hand functioning in children with cerebral palsy is proposed by Arnould et al. (2) while Johansson et al. (3) explore the effect of timing training on upper limb movement in three children with diplegic cerebral palsy. Parma et al. (4) compare the kinematics of the reach-to grasp movement in patients with vascular and idiopathic Parkinson’s disease whereas Aluru et al. (5) evaluate the effect of auditory constraints on motor performance at different stages after a stroke. Lawrence et al. (6) measure dexterous manipulation in a cross-sectional study comparing gender, age, and absence and presence of disease. Kirsh et al. (7) provide evidence to support the view that neurons outside the primary motor cortex – such as those populating the pontomedullary reticular formation and the spinal cord-drive movement and muscle synergies that primary motor cortex neurons then break up to create individual wrist and finger movements. Sacrey et al. (8) summarize current knowledge related to reaching and grasping in autism spectrum disorder. On the other hand, Whitwell et al. (9) reinstate patient DF’s amazing ability to use information regarding form and orientation of objects to guide skilled reaching actions despite her visual agnosia. In an opinion article, Moore (10) argues that nerve transfer is increasingly popular and is becoming the best treatment strategy for most brachial plexus damage as well as for patients with spinal cord injury at cervical levels. Vicario (11) provides a personal commentary on a paper from Hayashi et al. (12) and, in a review article, Karl and Whishaw (13) summarize the evidence that show that reaching and grasping are from distinct neural and evolutionary origins. Irvine et al. (14) contribute a methods article that assesses the reliability of the Irvine, Beatties, and Bresnahan (IBB) forelimb recovery scale. Fouad et al. (15) demonstrate that continuous viral-mediated brain-derived neurotrophic factor (BDNF) over-expression promotes spasticity in rats with spinal cord hemisections at cervical levels. Alstermark and Pettersson (16) bring evidence to show that lesions to the corticospinal tract that spare the cortico-reticulospinal pathway in the rat have no deleterious effects on skilled reaching and grasping. Finally, Tosolini et al. (17) describe how targeting the full length of the motor endplate region in the mouse forelimb with Fluoro-Gold increases the uptake of this neuroanatomical retrograde tracer in corresponding motor neurons. We are delighted to present “Arm and Hand Movement: Current Knowledge and Future Perspective” as a Research Topic in Frontiers in Neurology. We feel that this wide-ranging compilation of articles by leading experts in upperlimb/forelimb movement and working either in clinical or basic research settings has offered fresh perspectives on the topic. We are thankful for the support of all the scientists who have contributed to this Research Topic and have shared with us their expertise and point of views. Their contributions have deepened our appreciation of the challenge that restoring arm and hand function in different pathologies represents. We invite the readers to experience the diversity in methodological approaches and experimental designs that together have led to broaden our understanding of this particularly wide field of research.

Synaptic circuit organization of motor corticothalamic neurons.

Corticothalamic (CT) neurons in layer 6 constitute a large but enigmatic class of cortical projection neurons. How they are integrated into intracortical and thalamo-cortico-thalamic circuits is incompletely understood, especially outside of sensory cortex. Here, we investigated CT circuits in mouse forelimb motor cortex (M1) using multiple circuit-analysis methods. Stimulating and recording from CT, intratelencephalic (IT), and pyramidal tract (PT) projection neurons, we found strong CT↔ CT and CT↔ IT connections; however, CT→IT connections were limited to IT neurons in layer 6, not 5B. There was strikingly little CT↔ PT excitatory connectivity. Disynaptic inhibition systematically accompanied excitation in these pathways, scaling with the amplitude of excitation according to both presynaptic (class-specific) and postsynaptic (cell-by-cell) factors. In particular, CT neurons evoked proportionally more inhibition relative to excitation (I/E ratio) than IT neurons. Furthermore, the amplitude of inhibition was tuned to match the amount of excitation at the level of individual neurons; in the extreme, neurons receiving no excitation received no inhibition either. Extending these studies to dissect the connectivity between cortex and thalamus, we found that M1-CT neurons and thalamocortical neurons in the ventrolateral (VL) nucleus were remarkably unconnected in either direction. Instead, VL axons in the cortex excited both IT and PT neurons, and CT axons in the thalamus excited other thalamic neurons, including those in the posterior nucleus, which additionally received PT excitation. These findings, which contrast in several ways with previous observations in sensory areas, illuminate the basic circuit organization of CT neurons within M1 and between M1 and thalamus.

RING1 proteins contribute to early proximal-distal specification of the forelimb bud by restricting Meis2 expression.

Polycomb group (PcG) proteins play a pivotal role in silencing developmental genes and help to maintain various stem and precursor cells and regulate their differentiation. PcG factors also regulate dynamic and complex regional specification, particularly in mammals, but this activity is mechanistically not well understood. In this study, we focused on proximal-distal (PD) patterning of the mouse forelimb bud to elucidate how PcG factors contribute to a regional specification process that depends on developmental signals. Depletion of the RING1 proteins RING1A (RING1) and RING1B (RNF2), which are essential components of Polycomb repressive complex 1 (PRC1), led to severe defects in forelimb formation along the PD axis. We show that preferential defects in early distal specification in Ring1A/B-deficient forelimb buds accompany failures in the repression of proximal signal circuitry bound by RING1B, including Meis1/2, and the activation of distal signal circuitry in the prospective distal region. Additional deletion of Meis2 induced partial restoration of the distal gene expression and limb formation seen in the Ring1A/B-deficient mice, suggesting a crucial role for RING1-dependent repression of Meis2 and likely also Meis1 for distal specification. We suggest that the RING1-MEIS1/2 axis is regulated by early PD signals and contributes to the initiation or maintenance of the distal signal circuitry.