Modeling Parkinson’s Disease in Zebrafish

Parkinson’s Disease (PD) is one of the most common neurodegenerative disorders that affects the motor system, and includes cardinal motor symptoms such as resting tremor, cogwheel rigidity, bradykinesia and postural instability. Its prevalence is increasing worldwide due to the increase in life span. Although, two centuries since the first description of the disease, no proper cure with regard to treatment strategies and control of symptoms could be reached. One of the major challenges faced by the researchers is to have a suitable research model. Rodents are the most common PD models used, but no single model can replicate the true nature of PD. In this review, we aim to discuss another animal model, the zebrafish (Danio rerio), which is gaining popularity. Zebrafish brain has all the major structures found in the mammalian brain, with neurotransmitter systems, and it also possesses a functional blood-brain barrier similar to humans. From the perspective of PD research, the zebrafish possesses the ventral diencephalon, which is thought to be homologous to the mammalian substantia nigra. We summarize the various zebrafish models available to study PD, namely chemical-induced and genetic models. The zebrafish can complement the use of other animal models for the mechanistic study of PD and help in the screening of new potential therapeutic compounds.

FGF3 from the Hypothalamus Regulates the Guidance of Thalamocortical Axons

Thalamus is an important sensory relay station: afferent sensory information, except olfactory signals, is transmitted by thalamocortical axons (TCAs) to the cerebral cortex. The pathway choice of TCAs depends on diverse diffusible or substrate-bound guidance cues in the environment. Not only classical guidance cues (ephrins, slits, semaphorins, and netrins), morphogens, which exerts patterning effects during early embryonic development, can also help axons navigate to their targets at later development stages. Here, expression analyses reveal that morphogen Fibroblast growth factor (FGF)-3 is expressed in the chick ventral diencephalon, hypothalamus, during the pathfinding of TCAs. Then, using in vitro analyses in chick explants, we identify a concentration-dependent effect of FGF3 on thalamic axons: attractant 100 ng/mL FGF3 transforms to a repellent at high concentration 500 ng/mL. Moreover, inhibition of FGF3 guidance functions indicates that FGF3 signaling is necessary for the correct navigation of thalamic axons. Together, these studies demonstrate a direct effect for the member of FGF7 subfamily, FGF3, in the axonal pathfinding of TCAs.

Comprehensive Analysis of Neurotoxin-Induced Ablation of Dopaminergic Neurons in Zebrafish Larvae

Neurotoxin exposure of zebrafish larvae has been used to mimic a Parkinson’s disease (PD) phenotype and to facilitate high-throughput drug screening. However, the vulnerability of zebrafish to various neurotoxins was shown to be variable. Here, we provide a direct comparison of ablative effectiveness in order to identify the optimal neurotoxin-mediated dopaminergic (DAnergic) neuronal death in larval zebrafish. Transgenic zebrafish, Tg(dat:eGFP), were exposed to different concentrations of the neurotoxins MPTP, MPP+, paraquat, 6-OHDA, and rotenone for four days, starting at three days post-fertilization. The LC50 of each respective neurotoxin concentration was determined. Confocal live imaging on Tg(dat:eGFP) showed that MPTP, MPP+, and rotenone caused comparable DAnergic cell loss in the ventral diencephalon (vDC) region while, paraquat and 6-OHDA caused fewer losses of DAnergic cells. These results were further supported by respective gene expression analyses of dat, th, and p53. Importantly, the loss of DAnergic cells from exposure to MPTP, MPP+, and rotenone impacted larval locomotor function. MPTP induced the largest motor deficit, but this was accompanied by the most severe morphological impairment. We conclude that, of the tested neurotoxins, MPP+ recapitulates a substantial degree of DAnergic ablation and slight locomotor perturbations without systemic defects indicative of a Parkinsonian phenotype.

Mutations in MAGEL2 and L1CAM Are Associated With Congenital Hypopituitarism and Arthrogryposis

Context Congenital hypopituitarism (CH) is rarely observed in combination with severe joint contractures (arthrogryposis). Schaaf-Yang syndrome (SHFYNG) phenotypically overlaps with Prader-Willi syndrome, with patients also manifesting arthrogryposis. L1 syndrome, a group of X-linked disorders that include hydrocephalus and lower limb spasticity, also rarely presents with arthrogryposis. Objective We investigated the molecular basis underlying the combination of CH and arthrogryposis in five patients. Patients The heterozygous p.Q666fs*47 mutation in the maternally imprinted MAGEL2 gene, previously described in multiple patients with SHFYNG, was identified in patients 1 to 4, all of whom manifested growth hormone deficiency and variable SHFYNG features, including dysmorphism, developmental delay, sleep apnea, and visual problems. Nonidentical twins (patients 2 and 3) had diabetes insipidus and macrocephaly, and patient 4 presented with ACTH insufficiency. The hemizygous L1CAM variant p.G452R, previously implicated in patients with L1 syndrome, was identified in patient 5, who presented with antenatal hydrocephalus. Results Human embryonic expression analysis revealed MAGEL2 transcripts in the developing hypothalamus and ventral diencephalon at Carnegie stages (CSs) 19, 20, and 23 and in the Rathke pouch at CS20 and CS23. L1CAM was expressed in the developing hypothalamus, ventral diencephalon, and hindbrain (CS19, CS20, CS23), but not in the Rathke pouch. Conclusion We report MAGEL2 and L1CAM mutations in four pedigrees with variable CH and arthrogryposis. Patients presenting early in life with this combined phenotype should be examined for features of SHFYNG and/or L1 syndrome. This study highlights the association of hypothalamo-pituitary disease with MAGEL2 and L1CAM mutations.

Desikan-Killiany-Tourville Atlas Compatible Version of M-CRIB Neonatal Parcellated Whole Brain Atlas: The M-CRIB 2.0

Our recently published M-CRIB atlas comprises 100 neonatal brain regions including 68 compatible with the widely-used Desikan-Killiany adult cortical atlas. A successor to the Desikan-Killiany atlas is the Desikan-Killiany-Tourville atlas, in which some regions with unclear boundaries were removed, and many existing boundaries were revised to conform to clearer landmarks in sulcal fundi. Our first aim here was to modify cortical M-CRIB regions to comply with the Desikan-Killiany-Tourville protocol, in order to offer: a) compatibility with this adult cortical atlas, b) greater labelling accuracy due to clearer landmarks, and c) optimisation of cortical regions for integration with surface-based infant parcellation pipelines. Secondly, we aimed to update subcortical regions in order to offer greater compatibility with subcortical segmentations produced in FreeSurfer. Data utilized were the T2-weighted MRI scans in our M-CRIB atlas, for ten healthy neonates (postmenstrual age at MRI 40-43 weeks, 4 female), and corresponding parcellated images. Edits were performed on the parcellated images in volume space using ITK-SNAP. Cortical updates included deletion of frontal and temporal poles and ‘Banks STS’, and modification of boundaries of many other regions. Changes to subcortical regions included the addition of ‘ventral diencephalon’, and deletion of ‘subcortical matter’ labels. A detailed updated parcellation protocol was produced. The resulting whole-brain M-CRIB 2.0 atlas comprises 94 regions altogether. This atlas provides comparability with adult Desikan-Killiany-Tourville-labelled cortical data and FreeSurfer-labelled subcortical data, and is more readily adaptable for incorporation into surface-based neonatal parcellation pipelines. As such, it offers the ability to help facilitate a broad range of investigations into brain structure and function both at the neonatal time point and developmentally across the lifespan.

Genetic regulation of murine pituitary development

Significant progress has been made recently in unravelling the embryonic events leading to pituitary morphogenesis, bothin vivoandin vitro. This includes dissection of the molecular mechanisms controlling patterning of the ventral diencephalon that regulate formation of the pituitary anlagen or Rathke's pouch. There is also a better characterisation of processes that underlie maintenance of pituitary progenitors, specification of endocrine lineages and the three-dimensional organisation of newly differentiated endocrine cells. Furthermore, a population of adult pituitary stem cells (SCs), originating from embryonic progenitors, have been described and shown to have not only regenerative potential, but also the capacity to induce tumour formation. Finally, the successful recapitulationin vitroof embryonic events leading to generation of endocrine cells from embryonic SCs, and their subsequent transplantation, represents exciting advances towards the use of regenerative medicine to treat endocrine deficits. In this review, an up-to-date description of pituitary morphogenesis will be provided and discussed with particular reference to pituitary SC studies.

Heterogeneous Expression of Chondroitin Sulfate Glycosaminoglycans and Versican Proteoglycan during Early Development of Rathke’s Pouch

While much is known regarding morphogenetic factors involved in specification and differentiation of Rathke’s pouch, less attention has been given to extracellular matrix (ECM) interactions involved in its formation. The present research investigated localization of two different chondroitin sulfate glycosaminoglycans (CS-GAGs), TC2 and d1C4, and versican CS-proteoglycan (PG) to identify additional ECM molecules involved in formation of the pituitary rudiment. Immunohistochemical evaluation of anterior pituitary primordia between HH15 and HH28 showed these ECM molecules prevalent in basement membrane and surrounding ECM underlying Rathke’s epithelia and to a lesser extent between pouch epithelial cells. TC2/d1C4 CS-GAGs and versican showed changing and heterogeneous localization during pouch development that suggested specific roles in cell-ECM interaction during pituitary morphogenesis. TC2 antigen colocalized with versican at early stages in an asymmetric pattern, with particularly strong staining between ventral diencephalon and roof of Rathke’s pouch while d1C4 CS-GAG encompassed the entire pouch by HH22 indicating association with a different CSPG. The heparan sulfate proteoglycan, perlecan, used to verify basement membrane structure, was a consistent component of Rathke’s pouch. Data show a dynamic and heterogeneous pattern of CS-GAG and versican expression during early chick Rathke’s pouch development that suggests new possibilities for ECM function in its establishment and growth.