Localization and Characterization of Major Neurogenic Niches in the Brain of the Lesser-Spotted Dogfish Scyliorhinus canicula

Adult neurogenesis is defined as the ability of specialized cells in the postnatal brain to produce new functional neurons and to integrate them into the already-established neuronal network. This phenomenon is common in all vertebrates and has been found to be extremely relevant for numerous processes, such as long-term memory, learning, and anxiety responses, and it has been also found to be involved in neurodegenerative and psychiatric disorders. Adult neurogenesis has been studied extensively in many vertebrate models, from fish to human, and observed also in the more basal cartilaginous fish, such as the lesser-spotted dogfish, Scyliorhinus canicula, but a detailed description of neurogenic niches in this animal is, to date, limited to the telencephalic areas. With this article, we aim to extend the characterization of the neurogenic niches of S. canicula in other main areas of the brain: we analyzed via double immunofluorescence sections of telencephalon, optic tectum, and cerebellum with markers of proliferation (PCNA) and mitosis (pH3) in conjunction with glial cell (S100β) and stem cell (Msi1) markers, to identify the actively proliferating cells inside the neurogenic niches. We also labeled adult postmitotic neurons (NeuN) to exclude double labeling with actively proliferating cells (PCNA). Lastly, we observed the presence of the autofluorescent aging marker, lipofuscin, contained inside lysosomes in neurogenic areas

Distribution of Brain-Derived Neurotrophic Factor in the Brain of the Small-Spotted Catshark Scyliorhinus canicula, and Evolution of Neurotrophins in Basal Vertebrates

Neurotrophins (NTFs) are structurally related neurotrophic factors essential for differentiation, survival, neurite outgrowth, and the plasticity of neurons. Abnormalities associated with neurotrophin-signaling (NTF-signaling) were associated with neuropathies, neurodegenerative disorders, and age-associated cognitive decline. Among the neurotrophins, brain-derived neurotrophic factor (BDNF) has the highest expression and is expressed in mammals by specific cells throughout the brain, with particularly high expression in the hippocampus and cerebral cortex. Whole genome sequencing efforts showed that NTF signaling evolved before the evolution of Vertebrates; thus, the shared ancestor of Protostomes, Cyclostomes, and Deuterostomes must have possessed a single ortholog of neurotrophins. After the first round of whole genome duplication that occurred in the last common ancestor of Vertebrates, the presence of two neurotrophins in Agnatha was hypothesized, while the monophyletic group of cartilaginous fishes, or Chondrichthyans, was situated immediately after the second whole genome duplication round that occurred in the last common ancestor of Gnathostomes. Chondrichthyans represent the outgroup of all other living jawed vertebrates (Gnathostomes) and the sister group of Osteichthyans (comprehensive of Actinopterygians and Sarcopterygians). We were able to first identify the second neurotrophin in Agnatha. Secondly, we expanded our analysis to include the Chondrichthyans, with their strategic phylogenetic position as the most basal extant Gnathostome taxon. Results from the phylogenetic analysis confirmed the presence of four neurotrophins in the Chondrichthyans, namely the orthologs of the four mammalian neurotrophins BDNF, NGF, NT-3, and NT-4. We then proceeded to study the expression of BDNF in the adult brain of the Chondrichthyan Scyliorhinus canicula. Our results showed that BDNF is highly expressed in the S. canicula brain and that its expression is highest in the Telencephalon, while the Mesencephalic and Diencephalic areas showed expression of BDNF in isolated and well-defined cell groups. NGF was expressed at much lower levels that could be detected by PCR but not by in situ hybridization. Our results warrant further investigations in Chondrichthyans to characterize the putative ancestral function of neurotrophins in Vertebrates

Quantification of noradrenergic-, dopaminergic-, and tectal-neurons during aging in the short-lived killifish Nothobranchius furzeri

Parkinson's disease (PD) is characterized by phosphorylation and aggregation of the protein alpha-Synuclein and ensuing neuronal death progressing from the noradrenergic locus coeruleus to midbrain dopaminergic neurons. In 2019, Matsui and colleagues reported a spontaneous age-dependent degeneration of dopaminergic neurons and an even greater neurodegeneration of the noradrenergic neurons in the short-lived killifish Nothobranchius furzeri. Given the great possible relevance of a spontaneous model for PD, we assessed neurodegeneration of noradrenergic and dopaminergic neurons in two further laboratory strains of N. furzeri. We implemented, for the first time in N. furzeri, a whole-brain clarification technique and proceeded to entire 3D nuclei reconstruction to quantify total cell numbers in two different stains of N. furzeri. In both strains, we observed that age-dependent neurodegeneration is limited to the locus coeruleus and does not involve the posterior tuberculum. We also applied 3D counting to the optic tectum, an area of active adult neurogenesis, and detected an increase of neurons with age. Our results confirm age-dependent neurodegeneration of noradrenergic neurons, a condition reminiscent of the presymptomatic stage of PD indicating that N. furzeri could be used in the future to identify modifying factors for age-dependent neurodegeneration and open the intriguing possibility that natural genetic variation may influence the susceptibility of dopaminergic neurons

The age-regulated zinc finger factor ZNF367 is a new modulator of neuroblast proliferation during embryonic neurogenesis.

Global population aging is one of the major social and economic challenges of contemporary society. During aging the progressive decline in physiological functions has serious consequences for all organs including brain. The age-related incidence of neurodegenerative diseases coincides with the sharp decline of the amount and functionality of adult neural stem cells. Recently, we identified a short list of brain age-regulated genes by means of next-generation sequencing. Among them znf367 codes for a transcription factor that represents a central node in gene co-regulation networks during aging, but whose function in the central nervous system (CNS), is completely unknown. As proof of concept, we analysed the role of znf367 during Xenopus laevis neurogenesis. By means of a gene loss of function approach limited to the CNS, we suggested that znf367 might act as a key controller of the neuroblast cell cycle, particularly in the progression of mitosis and spindle checkpoint. A candidate gene approach based on a weighted-gene co-expression network analysis, revealed fancd2 and ska3 as possible targets of znf367. The age-related decline of znf367 correlated well with its role during embryonic neurogenesis, opening new lines of investigation also in adult neurogenesis to improved maintenance and even repair of neuronal function

Specific alterations of tyrosine hydroxylase immunopositive cells in the retina of NT-4 knock out mice

AbstractTo assess the effect of NT-4 deprivation on maturation of retinal circuitry, we investigated a mouse with targeted deletion of the gene encoding nt-4 (nt-4−/−). In particular, we studied neurons immunostained by an antibody recognizing tyrosine hydroxylase (TH), the rate limiting enzyme for dopamine (DA) synthesis. We found that TH immunopositive processes were altered in the retina of nt-4−/−. Alteration of TH immunopositive processes in nt-4−/− mice resulted in changes of DA turnover, as assessed by high-pressure liquid chromatography measurements. These findings suggest that retinal NT-4 plays a role in the morphological maturation of dopaminergic retinal cells

Large Differences in Aging Phenotype between Strains of the Short-Lived Annual Fish Nothobranchius furzeri

BACKGROUND: A laboratory inbred strain of the annual fish Nothobranchius furzeri shows exceptionally short life expectancy and accelerated expression of age markers. In this study, we analyze new wild-derived lines of this short-lived species. METHODOLOGY/PRINCIPAL FINDINGS: We characterized captive survival and age-related traits in F1 and F2 offspring of wild-caught N. furzeri. Wild-derived N. furzeri lines showed expression of lipofuscin and neurodegeneration at age 21 weeks. Median lifespan in the laboratory varied from to 20 to 23 weeks and maximum lifespan from 25 to 32 weeks. These data demonstrate that rapid age-dependent decline and short lifespan are natural characteristics of this species. The N. furzeri distribution range overlaps with gradients in altitude and aridity. Fish from more arid habitats are expected to experience a shorter survival window in the wild. We tested whether captive lines stemming from semi-arid and sub-humid habitats differ in longevity and expression of age-related traits. We detected a clear difference in age-dependent cognitive decline and a slight difference in lifespan (16% for median, 15% for maximum lifespan) between these lines. Finally, we observed shorter lifespan and accelerated expression of age-related markers in the inbred laboratory strain compared to these wild-derived lines. CONCLUSIONS/SIGNIFICANCE: Owing to large differences in aging phenotypes in different lines, N. furzeri could represent a model system for studying the genetic control of life-history traits in natural populations

The microRNA miR-21 Is a Mediator of FGF8 Action on Cortical COUP-TFI Translation

The morphogen FGF8 plays a pivotal role in neocortical area patterning through its inhibitory effect on COUP-TFI/Nr2f1 anterior expression, but its mechanism of action is poorly understood. We established an in vitro model of mouse embryonic stem cell corticogenesis in which COUP-TFI protein expression is inhibited by the activation of FGF8 in a time window corresponding to cortical area patterning. Interestingly, overexpression of the COUP-TFI 3′UTR reduces the inhibitory effect of FGF8 on COUP-TFI translation. FGF8 induces the expression of few miRNAs targeting COUP-TFI 3′UTR in silico. We found that the functional inhibition of miR-21 can effectively counteract the inhibitory effect of FGF8 in vitro and regulate COUP-TFI protein levels in vivo. Accordingly, miR-21 expression is complementary to COUP-TFI expression during corticogenesis. These data support a translational control of COUP-TFI gradient expression by FGF8 via miR-21 and contribute to our understanding of how regionalized expression is established during neocortical area mapping

Age-related central regulation of orexin and NPY in the short-lived African killifish Nothobranchius furzeri

Orexin A (OXA) and neuropeptide Y (NPY) are two hypothalamic neuropeptides involved in the regulation of feeding behavior and food intake in all vertebrates. Accumulating evidences document that they undergo age-related modifications, with consequences on metabolism, sleep/wake disorders and progression of neurodegenerations. The present study addressed the age related changes in expression and distribution of orexin A (its precursor is also known as hypocretin\u2014HCRT) and NPY, and their regulation by food intake in the short-lived vertebrate model Nothobranchius furzeri. Our experiments, conducted on male specimens, show that: (a) HCRT and OXA and NPY mRNA and protein are localized in neurons of diencephalon and optic tectum, as well as in numerous fibers projecting through the entire neuroaxis, and are colocalized in specific nuclei; (b) in course of aging, HCRT and NPY expressing neurons are localized also in telencephalon and rhombencephalon; (c) HCRT expressing neurons increased slightly in the diencephalic area of old animals and in fasted animals, whereas NPY increased sharply; (d) central HCRT levels are not regulated neither in course of aging nor by food intake; and (e) central NPY levels are augmented in course of aging, and regulated by food intake only in young. These findings represent a great novelty in the study of central orexinergic and NPY-ergic systems in vertebrates', demonstrating an uncommon and unprecedented described regulation of these two orexigenic neuropeptides

Systemic but not intraocular Epo Gene Transfer Protects the Retina from Light-and Genetic-Induced Degeneration

n/