J. Méndez

NOR activity in larval and juvenile mussels (Mytilus gallopro vincialis Lmk.)

Abstract The silver staining patterns of the nucleolus organizer regions (NORs), an indication of rDNA transcriptional activity, were studied in metaphase chromosomes from larvae and juveniles of a bivalve mussel, Mytilus galloprovincialis. Two submetacentric/subtelocentric pairs of chromosomes, out of the the total complement of 14 pairs, were characterized by the presence of silver-stained NORs. A considerable degree of inter- and intraindividual variation in NOR activity was noted. Mean NOR activity in larvae (3.27 active NORs per metaphase) was demonstrated to be higher than in the gill tissue of the juvenile mussels (1.93).

Analysis of NORs and NOR-associated heterochromatin in the mussel Mytilus galloprovincialis Lmk

The chromosomes of the mussel Mytilus galloprovincialis were analysed by means of chromomycin A3 (CMA), distamycin A/DAPI (DA/DAPI), DAPI/actinomycin D (DAPI/AMD) and chromomycin A3/distamycin A/DAPI(CDD) fluorescence banding techniques, C-banding, silver staining, N-banding and in situ hybridization with 18S+28S rDNA and telomere probes. 18S+28S rDNA clusters were located on the telomeres of two pairs of submeta/subtelocentric chromosomes. The nucleolar organizing regions (NORs) were associated with bright CMA fluorescence, dull DAPI fluorescence and C- and N-positive bands, but not all four NOR-associated heterochromatin bands showed bright CMA fluorescence in a given cell; intra- and interindividual variability was found in this character. Additional non-ribosomal C-bands did not show any differential fluorescent behaviour.

Proliferation kinetics of mussel (Mytilus galloprovincialis) gill cells

A technique of sister chromatid differentiation (SCD) using bromodeoxyuridine (BrdU) incorporation and a modification of the fluorescence plus Giemsa (FPG) method was employed to determine cell-proliferation kinetics in gill tissue of the mussel Mytilus galloprovincialis. Dose-dependent proliferation inhibition was examined. In vivo administration of BrdU for 12, 24, 36, 48, 60, 72, 84, and 96 h was studied. Our data show that the highest yield of second-generation metaphase plates is obtained after 60 h BrdU treatment; the duration of a cell cycle is 24 to 30 h. On the basis of these data, a BrdU incorporation period of 48 to 60 h would seem to be most appropriate for the sister chromatid exchange (SCE) tests carried out in gill cells of M. galloprovincialis, whereas the 12 to 24 h exposure would give the best results for replication band analysis.

Banding pattern of mussel (Mytilus galloprovincialis) chromosomes induced by 2 × SSC/Giemsa-stain treatment

Mytilus galloprovincialis were collected from an intertidal population in NW Spain in 1988, and chromosomes from the gill tissue of 37 individuals were studied. The present paper describes the banding pattern of aM. galloprovincialis population which enabled us to identify all pairs of chromosomes. Banding was induced by means of a 2 × SSC (0.3M sodium chloride:0.03M sodium citrate)/Giemsa-staining technique, and a diagrammatic representation was constructed based on mean number of bands. The application of this banding technique may prove useful in future research related to the cytogenetics and cytotaxonomy of mussels and other molluscs.

C-band polymorphism in the chromosomes of the mussel Mytilus galloprovincialis Lmk.

SUMMARYThe chromosomes of 346 specimens of Mytilus galloprovincialis, collected at four NW Iberian peninsula sites, were studied using a C-banding technique. Polymorphism for C-banding was detected. According to the banding patterns, three classes of mussels could be distinguished: 1) individuals showing two pairs of submeta/subtelocentric chromosomes bearing NOR-associated heterochromatic regions terminal to their long arms, 2) mussels presenting additional C-bands located at other positions on the NOR-bearing chromosomes or on other chromosomes, and 3) mosaic mussels. The location of the additional C-band positive regions was similar in the four populations studied.

Evolution of digestibility by Hind III: an analysis by light and electron microscopy

Digestion of Chinese hamster metaphase chromosomes from the Don cell line by Hind III restriction endonuclease followed by Giemsa staining were analysed by light and electron microscopy. The evolution of digestibility was studied and four digestion stages were characterized by different levels of chromosome structure. Three different condensation stages were established according to morphological criteria of length, width and separation among chromatids. It was observed that there are statistically significant differences in the digestion progress at the three condensation stages previously defined.