Genome size and A-T rich DNA in selachians

The nuclear DNA content of 23 selachian species (10 Batoidea, 11 Galeomorphii, and 2 Squalomorphii) was histophotometrically studied. Their genome sizes range from 7.5 pg/N in Raja fillae (Batoidea) to 34.1 pg/N in Oxynotus centrina (Squalomorphii).Results show slight differences in the pattern of quantitative variations between the superorders Batoidea and Galeomorphii; Squalomorphii preserve their peculiar wide interspecific variability at the intrafamilial level, with values sited between 13.1 and 34.1 pg/N.In 21 species also the DNA base composition was determined by means of DAPI. The study shows that in the species examined the DAPI positive fraction varies from a minimum of 27.7% in Oxynotus centrina, which possesses the largest genome size among all the Selachians studied, to a maximum of 72.5% in Carcharhinus limbatus. As a whole the data show an inverse correlation between the DNA content and the DAPI positive fraction, a condition common to all cold-blooded vertebrates.The low percentage of DAPI positive DNA found in Oxynotus centrina could be attributable to a lower stainability by the fluorochrome caused by a higher chromatin condensation in the erythrocytes.The validity of the DAPI method was verified by comparison with the biochemical assay according to the thermal denaturation method in 6 selachian species.

[1]  R. Hinegardner,et al.  The cellular DNA content of sharks, rays and some other fishes. , 1976, Comparative biochemistry and physiology. B, Comparative biochemistry.

[2]  J. Marmur.  A procedure for the isolation of deoxyribonucleic acid from micro-organisms , 1961 .

[3]  J. Maisey.  Higher elasmobranch phylogeny and biostratigraphy , 1984 .

[4]  E. Olmo,et al.  Repetitive DNA and polyploidy in selachians. , 1982, Comparative biochemistry and physiology. B, Comparative biochemistry.

[5]  E. Olmo.  Nucleotype and cell size in vertebrates: a review. , 1983, Basic and applied histochemistry.

[6]  J. Marmur,et al.  [109] Use of ultraviolet absorbance-temperature profile for determining the guanine plus cytosine content of DNA , 1968 .

[7]  K. Tsou,et al.  A comparative study of DAPI, DIPI, and Hoechst 33258 and 33342 as chromosomal DNA stains. , 1985, Stain technology.

[8]  A. Coleman,et al.  Applications of fluorochromes to pollen biology. I. Mithramycin and 4',6-diamidino-2-phenylindole (DAPI) as vital stains and for quantitation of nuclear DNA. , 1985, Stain technology.

[9]  J. Maisey.  Chondrichthyan phylogeny: a look at the evidence , 1984 .

[10]  J. Lewis.  Comparative hematology--studies on Camelidae. , 1976, Comparative biochemistry and physiology. A, Comparative physiology.

[11]  U. Leemann,et al.  Cytofluorometric determination of DNA base content in plant nuclei and chromosomes by the fluorochromes DAPi and chromomycin A3. , 1982, Experimental cell research.

[12]  V. Stingo,et al.  Genome size of some selachian fishes , 1980 .

[13]  J. Marmur.  [100] A procedure for the isolation of deoxyribonucleic acid from microorganisms , 1963 .

[14]  W. Nagl.  Chromatin organization and the control of gene activity. , 1985, International review of cytology.

[15]  E. Olmo,et al.  Cytofluorometric DNA base determination in vertebrate species with different genome sizes. , 1987, Basic and applied histochemistry.