Microglia of teleosts: facing a challenge in neurobiology.

This review is concerned with recent literature on teleost fish CNS microglia. It covers not only various aspects of these cells, notably comparing them with mammalian microglia, but also points out the several potentialities neural tissue of teleosts exhibits in neurobiological research. The relationships between neurons and glial cells are considered in fish, aiming at an integrated picture of the complex ways neurons and glia communicate and collaborate in normal and injured neural tissues. In addition, attention has been paid to different teleost models according to their availability, easy maintenance in experimental conditions, possibilities of embryos manipulation and sequenced genome. The recent setting up of successful protocols for fish glia and mixed neuron-glia cultures, together with the molecular facilities offered from genome knowledge, should provide a new boost to studies about microglia and neuron-microglia relationships.

The supramedullary cells of the teleost Coris julis (L.): a noradrenergic neuronal system.

This study, carried out on Coris julis (Labridae), is a contribution to the immunocytochemical characterization of fish supramedullary neurons. The significance of these giant cells has been debated since the beginning of the twentieth century. Our research provides the first evidence for a noradrenergic feature of this neuronal system. The possible role of supramedullary neurons as components of the autonomic nervous system is discussed. Moreover, the present results, taken together with our previous studies, surmise that this the first known case of colocalization of a neuropeptide (gastrin/CCK-like) and noradrenaline in the nervous system of teleosts.

DNA endoreplication in the clustered supramedullary neurons of the pufferfish Diodon holacanthus L. (osteichthyes).

DNA contents, ranging from 4C to more than 500C, were determined by a quantitative microfluorimetric assay in supramedullary neuron nuclei of the pufferfish Diodon holacanthus. The distribution of C values after ethidium bromide staining indicates an inter- and intra-individual variation in DNA contents which do not correspond to duplications of the total genome, suggesting that DNA replication is specific for particular genes (endoreplication). Moreover, the DNA content appears to be correlated with nuclear size. A relationship between the DNA amounts and the presence of AT- and GC-rich sequences has been shown. This work demonstrates, for the first time, DNA endoreplication in a specific neuronal type in vertebrates.

An anti-Bcl-2 antibody prevents 2-deoxy-D-ribose-induced apoptosis in the IPLB-LdFB insect cell line.

Confocal microscopy reveals that the anti-Bcl-2 antibody (pAb) is able to diffuse across the plasma membrane of the fat body cell line IPLB-LdFB from the insect Lymantria dispar, demonstrating the presence of Bcl-2-like molecules in the cytoplasm. Immunoperoxidase procedure confirms the cellular localization. Furthermore, an immunoprecipitation corresponding to a molecular weight of 29 KDa is observed with western blot analysis using the anti-Bcl-2 pAb. Cytofluorimetric experiments show that anti-Bcl-2 pAb counteracts 2-deoxy-D-ribose-induced apoptosis and provokes morphological changes in the insect cell line, i. e. a reduction in cell size, the disappearance of the vacuola and changes in shape. At the same time, the antibody provokes mitochondrial membrane depolarization, and N-acetyl-L-cysteine is unable to reconstitute the physiological conditions. The present findings suggest that Bcl-2-like proteins play a main role in maintaining of the integrity of cellular components, e.g. mitochondria, rather than in controlling programmed cell death.

Ultrastructural and cytochemical features of the supramedullary neurons of the pufferfish Diodon holacanthus (L.) (Osteichthyes).

Exceptionally high DNA contents were found in supramedullary neuron (SN) nuclei of the pufferfish Diodon holacanthus by quantitative microfluorimetric assay. This phenomenon has been explained by endoreplication, the functional significance of which is still unclear. In this view, the peptidergic nature and large dimensions make the teleostean clustered SN an interesting model for investigating the relationships between endoreplication, nuclear morphology and biosynthetic cellular activity. In this paper, we present a cytochemical and ultrastructural study on the SN of D. holacanthus (Tetraodontiformes). The nucleolar and nucleus structures suggest an intense production of ribosomal components in order to satisfy high cellular demands for protein synthesis. Accordingly, the cytoplasmic compartment presents an extensive rough endoplasmic reticulum, well-developed Golgi apparatus and a remarkable vesicular traffic. These features suggest that SN are engaged in an intense process of protein biosynthesis. The SN are completely surrounded by processes of different types of glial cells. The glial cells may be considered part of the SN cluster.

Glial cells: basic components of clusters of supramedullary neurons in pufferfish.

In this paper a cytochemical and ultrastructural study of clustered supramedullary neurons (SN) of Tetraodon fluviatilis (Tetraodontiformes) is presented. SN are large-sized nerve cells that have a high metabolic rate and are intensely engaged in protein biosynthesis. The SN are completely surrounded by two types of glial cell, which have been ultrastructurally, histochemically and immunohistochemically identified as astrocyte-like cells and microglial cells. The glial cells are located very close to the SN and sometimes contact them, which suggests that they do not only provide mechanical support but are also trophic for the SN and serve their functioning. We consider these glial cells as a constitutive and functional part of the cluster of SN, and therefore propose that the SN cluster constitute a suitable model to study in detail the morphological and functional relationships between neurons and glial cells in Anamnia.

Cytogenetic analysis of the pufferfish Tetraodon fluviatilis (Osteichthyes).

Because of their compact genome, pufferfish (Tetraodontiformes) have been proposed as a model for the study of the vertebrate genome. The genome of pufferfish is peculiar as it has the structural complexity of the genomes of higher vertebrates, but has small introns and lacks large clusters of highly repetitive sequences. Despite such interest, information about the genetics of pufferfish is still scanty. To fill this gap, we have performed a cytogenetic analysis of the pufferfish, Tetraodon fluviatilis, which can be maintained in an aquarium for a long time and, unlike the pufferfish, Fugu rubripes, it is not difficult to obtain. Karyotype analysis shows that T. fluviatilis has 2n = 42 with two metacentric chromosomes, four submetacentrics, two subtelocentrics and 34 acrocentrics. C-banding, followed by DAPI staining, showed that heterochromatin is essentially AT-rich and is located at centromeres. Staining of the same metaphase plates with CMA3 showed the presence of four heterochromatic regions located on two pairs of submetacentric chromosomes. Silver staining and FISH with a 28S rDNA probe showed that these GC-rich regions are nucleolar organizing regions (NORs). Finally, regardless of the technique used, no difference in the chromosome complement was found between males and females.