Milena Marini

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.

Histochemical and immunocytochemical localization of nitric oxide synthase in the supramedullary neurons of the pufferfish Tetraodon fluviatilis

The presence of the nitric oxide (NO) converting enzyme, constitutive neuronal NO synthase (nNOS), was investigated in the supramedullary neurons (SN) cluster of the pufferfish Tetraodon fluviatilis. The identification of NADPH diaphorase- (NADPHd-) positivity and the demonstration of nNOS with the BAS technique and with immunofluorescence together, strongly indicate the presence of a constitutive NO converting enzyme in SN cellular bodies and axons, and provides evidence that the SN cluster represents a distinct nitrergic neuronal system in the vertebrate CNS. The possible roles of NO in the cluster are discussed, including an involvement in communication among neurons and between neurons and the glial cells in the cluster.

Neuroanatomical and immunohistochemical studies on the dorsal neurons in the spinal cord of Trigla lucerna L. and Scorpaena porcus L. (Scorpaeniformes)

Peculiar dorsal neurons present in the dorsal spinal cord of Trigla lucerna L. and Scorpaena porcus L. were investigated by neuroanatomical and immunohistochemical methods. These neurons were previously defined as commissural cells, but have now been identified as supramedullary neurons. The following fundamental criteria for identifying the supramedullary neurons of Teleosts are proposed: a) dorsomedial location in the spinal cord; b) large size of the soma and axon; c) immunoreactivity to gastrin/CCK-like peptides.

Localization of the (TTAGGG)n telomeric repeat in the chromosomes of the pufferfish Tetraodon fluviatilis (Hamilton Buchanan) (Osteichthyes)

Abstract In order to characterise the telomeric repeats of the pufferfish Tetraodon fluviatilis, fluorescent in situ hybridization (FISH) was carried out on metaphase chromosomes using a PCR generated probe (TTAGGG)n. Distinct signals have been observed on the tel-omeres of all the chromosomes and hybridization signals appears of uniform size and intensity. Moreover FISH experiment does not evidence any interstitial non-telomeric signal. As non-telomeric FISH signal has been used as a marker for karyotype evolution and for determining the evolutionary status of fish species, it could be supposed that the absence of non telomeric signals makes T. fluviatilis (Tetraodontiformes) an evolutionary ancient species in respect to Perciformes.

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.

The mauthner neurons in salamandra

Abstract The Mauthner neurons are described in Salamandra atra and Salamandra salamandra, terrestrial and viviparous urodelans. In both species of Salamandra the M cells are present in every larval stage, and in metamorphosed and adult specimens. These cells are very similar in size and aspect to those described in oviparous and aquatic Salamandridae. The functional and phyletic hypotheses, in order to justify the presence in Salamandra of this apparatus, typical of tail swimming Anamnia, are discussed.

Preliminary findings on the development of the parasitic copepod Lernaea cyprinacea L. from cleavage to hatching

Abstract We report preliminary findings on the development of Lernaea cyprinacea from cleavage to hatching. The eggs are centrolecithal with superficial cleavage. Nucleoli were found in the nuclei of the perilecithal syncytium. Gastrulation occurs by in situ aggregation of cells, without evident morphogenetic movements.

Rohon-Beard neurons in viviparous and oviparous urodeles

Abstract The transient sensory system of the Rohon-Beard neurons is described in the viviparous Salamandra salamandra and Salamandra atra. The features of this system do not differ from those in the oviparous Salamandridae investigated (Triturus cristatus). The presence of such an early differentiated sensory system in viviparous Anamnia that develop isolated from the external environment may be related to the recent acquisition of viviparity by these species.