Biology subjects

Candal, E.

Publications and source records attributed to Candal, E..

7 recordsLinked to original sources

bioRxiv2024

A single-nucleus RNA sequencing atlas of the postnatal retina of the shark Scyliorhinus canicula

The retina, whose basic cellular structure is highly conserved across vertebrates, constitutes an accessible system for studying the central nervous system. In recent years, single-cell RNA-sequencing studies have uncovered cellular diversity in the retina of a variety of species, providing new insights on retinal evolution and development. However, similar data in cartilaginous fishes, the sister group to all other extant jawed vertebrates, are still lacking. Here, we present a single-nucleus RNA-sequencing atlas of the postnatal retina of the catshark Scyliorhinus canicula, consisting of the expression profiles for 17,438 individual cells from three female, juvenile catshark specimens. Unsupervised clustering revealed 22 distinct cell types comprising all major retinal cell classes, as well as retinal progenitor cells (whose presence reflects the persistence of proliferative activity in postnatal stages in sharks) and oligodendrocytes. Thus, our dataset serves as a foundation for further studies on the development and function of the catshark retina. Moreover, integration of our atlas with data from other species will allow for a better understanding of vertebrate retinal evolution.

neuroscience↗

bioRxiv2023

Analysis of a shark reveals ancient habenular asymmetries in gnathostomes and points to Wnt regulation as a driving force in their diversification

The origin of left-right asymmetries in the vertebrate habenula remains largely unknown. Using a transcriptomic approach, we show that in a cartilaginous fish, the catshark Scyliorhinus canicula, habenulae exhibit marked asymmetries both in their medial and their lateral component. Comparisons across gnathostomes suggest that asymmetries in the catshark lateral habenulae reflect an ancestral gnathostome trait, independently lost in tetrapods and neopterygians. Analysis of the mechanisms underlying their formation highlights an essential role of Wnt signaling. Wnt activity is submitted to a dynamic, asymmetric regulation during habenula development, with a Nodal dependent left repression at a stage when precursors for lateral habenulae have exited cell cycles. Pharmacological treatments during this time window reveal that Wnt signaling promotes lateral right neuronal identities in the right lateral habenula, while its repression by Nodal in the left one promotes lateral left neuronal identities. Based on comparisons with the zebrafish and the mouse, we propose that habenular asymmetry formation and diversification in gnathostomes involve the same developmental logic, relying on a conserved temporal regulation of neurogenesis, shaping neuronal identities on both sides, and its modification by a dynamic Wnt activity, right-restricted in the ancestral state and prone to variations in time and space during evolution.

developmental biology↗

bioRxiv2022

Use of vivo-morpholinos for gene knockdown in the postnatal shark retina

Work in the catshark Scyliorhinus canicula has shown that the evolutionary origin of postnatal neurogenesis in vertebrates is earlier than previously thought. Thus, the catshark can serve as a model of interest to understand postnatal neurogenic processes and their evolution in vertebrates. One of the best characterized neurogenic niches of the catshark CNS is found in the peripheral region of the retina. Unfortunately, the lack of genetic tools in sharks limits the possibilities to deepen in the study of genes involved in the neurogenic process. Here, we report a method for gene knockdown in the juvenile catshark retina based on the use of Vivo-Morpholinos. To establish the method, we designed Vivo-Morpholinos against the proliferation marker PCNA. We first evaluated the possible toxicity of 3 different intraocular administration regimes. After this optimization step, we show that a single intraocular injection of the PCNA Vivo-Morpholino decreases the expression of PCNA in the peripheral retina, which leads to reduced mitotic activity in this region. This method will help in deciphering the role of other genes potentially involved in postnatal neurogenesis in this model. Summary statementIn this study, we report the development of a method for the use of Vivo-Morpholinos in the postnatal shark retina, which will allow to decipher the role of different genes in retinal neurogenesis in sharks.

neuroscience↗

bioRxiv2021

Decline in constitutive proliferative activity in the zebrafish retina with ageing

It is largely assumed that the teleost retina shows continuous and active proliferative and neurogenic activity throughout life. But when deepening in the teleost literature one finds that assumptions about a highly active and continuous proliferation in the adult retina are based on studies in which proliferation was not quantified in a comparative way at the different life stages or was mainly studied in juveniles/young adults. Here, we performed a systematic and comparative study of the constitutive proliferative activity of the retina from early developing (2 days post-fertilization) to aged (up to 3-4 years post-fertilization) zebrafish. Mitotic activity and cell cycle progression were analyzed by using immunofluorescence against pH3 and PCNA, respectively. We observed a decline in cell proliferation in the retina with ageing, even despite the occurrence of a wave of secondary proliferation during sexual maturation. During this wave of secondary proliferation the distribution of proliferating and mitotic cells changes from the inner to the outer nuclear layer in the central retina. Importantly, in aged zebrafish there is a virtual disappearance of mitotic activity. Our results showing a decline in proliferative activity of the zebrafish retina with ageing are of crucial importance since it is generally assumed that the fish retina has continuous proliferative activity throughout life.

neuroscience↗

bioRxiv2020

Loss of active neurogenesis in the adult shark retina

Neurogenesis is the process by which progenitor cells generate new neurons. As development progresses neurogenesis becomes restricted to concrete neurogenic niches, where it persists during postnatal life. The retina of teleost fishes is thought to proliferate and produce new cells throughout life. Whether this capacity may be an ancestral characteristic of jawed vertebrates, shared with chondrichthyans, which diverged from osteichthyans prior to the gnathostome radiation is completely unknown. Previous work from our group revealed that the juvenile retina of the catshark Scyliorhinus canicula shows active proliferation and neurogenesis. Here, we compared the morphology and proliferative status of the retina between catshark juveniles and adults. Histological analyses revealed an important reduction in the size of the peripheral retina (where progenitor cells are mainly located), an increase in the thickness of the plexiform layers and a decrease in the thickness of the inner nuclear layer in adults. Contrary to what has been reported in teleost fish, we did not observe active mitotic activity in the catshark retina after sexual maturation, suggesting that there is no significant proliferation and neurogenesis in adult specimens. Based on these results, we carried out RNA-Sequencing (RNA-Seq) analyses comparing the retinal transcriptome of juveniles and adults, which revealed a statistically significant decrease in the expression of many genes involved in cell proliferation and neurogenesis in adult catsharks. Our RNA-Seq data provides an excellent resource to identify new signaling pathways controlling neurogenesis in the vertebrate retina.

developmental biology↗

bioRxiv2019

Differential expression of five prosomatostatin genes in the central nervous system of the catshark Scyliorhinus canicula

Five prosomatostatin genes (PSST1, PSST2, PSST3, PSST5 and PSST6) have been recently identified in elasmobranchs (Tostivint, Gaillard, Mazan, & Pezeron, 2019). In order to gain insight into the contribution of each somatostatin to specific nervous systems circuits and behaviors in this important jawed vertebrate group, we studied the distribution of neurons expressing PSST mRNAs in the catshark Scyliorhinus canicula using in situ hybridization with specific probes for the five PSSTs transcripts. Additionally, we combined in situ hybridization with tyrosine hydroxylase (TH) immunochemistry for better localization of some PSSTs-positive populations. The five PSST genes showed expression in the brain, although with important differences in distribution. PSST1 and PSST6 were widely expressed in different brain regions. Instead, PSST2 and PSST3 were expressed only in the ventral hypothalamus and in some hindbrain lateral reticular neurons, whereas PSST5 was only expressed in the region of the entopeduncular nucleus. PSST1 and PSST6 were expressed by numerous pallial neurons, although in different populations judging from the colocalization of tyrosine hydroxylase (TH) immunoreactivity and PSST6 expression in pallial neurons and the absence of colocalization between TH and PSST1 expression. Differential expression of PSST1 and PSST6 was also observed in the subpallium, hypothalamus, diencephalon, optic tectum, midbrain tegmentum and rhombencephalon. Expression of PSST1 was observed in numerous cerebrospinal fluid-contacting (CSF-c) neurons of the paraventricular organ of the hypothalamus and the central canal of the spinal cord. These wide differences in expression of PSST genes together with the numerous brain nuclei expressing PSSTs, indicate that catshark somatostatinergic neurons are implicated differentially in a number of neural circuits.

neuroscience↗

bioRxiv2019

Characterization of neurogenic niches in the telencephalon of juvenile and adult sharks

Neurogenesis is a multistep process by which progenitor cells become terminally differentiated neurons. Adult neurogenesis has gathered increasing interest with the aim of developing new cell-based treatments for neurodegenerative diseases in humans. Active sites of adult neurogenesis exist from fish to mammals, although in the adult mammalian brain the number and extension of neurogenic areas is considerably reduced in comparison to non-mammalian vertebrates, and they become mostly reduced to the telencephalon. Much of our understanding in this field is based in studies on mammals and zebrafish, a modern bony fish. The use of the cartilaginous fish Scyliorhinus canicula (representative of basal gnathostomes) as a model expands the comparative framework to a species that shows highly neurogenic activity in the adult brain. In this work, we studied the proliferation pattern in the telencephalon of juvenile and adult specimens of S. canicula by using antibodies against the proliferation marker PCNA. We have characterized proliferating niches by using stem cell markers (Sox2), glial markers (GFAP, BLBP and GS), intermediate progenitor cell markers (Dlx2 and Tbr2) and markers for migrating neuroblasts (DCX). Based in the expression pattern of these markers, we demonstrate the existence of different cell subtypes within the PCNA immunoreactive zones including non-glial stem cells, glial progenitors, intermediate progenitor-like cells and migratory neuroblasts, which were widely distributed in the ventricular zone of the pallium, suggesting that the main progenitor types that constitute the neurogenic niche in mammals are already present in cartilaginous fishes.

neuroscience↗