Anguilla anguilla L., and A. rostrata Le Sueur are two Anguilliform species living in European and American fresh waters respectively. Within the Osteichthyes, the Anguillidae show peculiar and sometimes contradictory characteristics. In fact, they belong to taxonomical division I (Greenwood et al., 1966), which is not related to the remaining divisions and they show some primitive characters. On the other hand, they present compositional compartmentalization of the genome (Medrano et al., 1988; Bernardi et al., 1990) and G and fluorochrome banded chromosomes (Sola et al., 1984; Mayr et al., 1990) characteristic of higher vertebrates. Their reproduction occurs in two partially overlapped areas of the Sargasso sea. Although being very closely related, as evidenced by the presence, in low frequence, of hybrids (Avise et al., 1990), A. anguilla and A. rostrata seem to represent two distinct species, as suggested by studies carried out using allozymes (Williams and Koehn, 1984) and mitochondrial DNA polymorphisms (Avise et al., 1986; Tagliavini et al., 1995). A great similarity exists between the two species at the level of karyotypes and metaphase classical banding patterns, but differences in centromeric heterochromatin composition/organization have been shown by means of the G-banding technique (Sola et al., 1984). Therefore, to deepen our knowledge on A. rostrata chromosomes, restriction endonuclease digestion (RE) was used in situ, a technique capable of providing information on the existence and the localization of repetitive DNA along the chromosome axis (Mezzanotte et al., 1983a, b; Lopez Fernandez et al., 1991). The karyotypes of seven A. rostrata individuals (three males and four females) from North America were analysed. Sex was determined by histological analysis of gonads and species were identified by vertebral counts. Metaphase chromosomes were obtained from lymphocyte cultures, according to Cau et al. (1988), and the experiments with REs were carried out according to Cau et al. (1992). Slides were stained in 25% Wright's stain (in 0.06 M phosphate buffer, pH 6.8) for 8 min, briefly rinsed in distilled water and air-dried. AluI produces a pattern resembling C-banding which tends to disappear when incubation is carried out for >3 h, in fact, after overnight incubation it produces relatively uniform faint staining in all chromosomes [Fig. 1(a)].
The different banding patterns produced by restriction endonuclease digestion in mitotic chromosomes of the American and European eel
SALVADORI, SUSANNA;DEIANA, ANNA MARIA;COLUCCIA, ELISABETTA;CAU, ANGELO
1997-01-01
Abstract
Anguilla anguilla L., and A. rostrata Le Sueur are two Anguilliform species living in European and American fresh waters respectively. Within the Osteichthyes, the Anguillidae show peculiar and sometimes contradictory characteristics. In fact, they belong to taxonomical division I (Greenwood et al., 1966), which is not related to the remaining divisions and they show some primitive characters. On the other hand, they present compositional compartmentalization of the genome (Medrano et al., 1988; Bernardi et al., 1990) and G and fluorochrome banded chromosomes (Sola et al., 1984; Mayr et al., 1990) characteristic of higher vertebrates. Their reproduction occurs in two partially overlapped areas of the Sargasso sea. Although being very closely related, as evidenced by the presence, in low frequence, of hybrids (Avise et al., 1990), A. anguilla and A. rostrata seem to represent two distinct species, as suggested by studies carried out using allozymes (Williams and Koehn, 1984) and mitochondrial DNA polymorphisms (Avise et al., 1986; Tagliavini et al., 1995). A great similarity exists between the two species at the level of karyotypes and metaphase classical banding patterns, but differences in centromeric heterochromatin composition/organization have been shown by means of the G-banding technique (Sola et al., 1984). Therefore, to deepen our knowledge on A. rostrata chromosomes, restriction endonuclease digestion (RE) was used in situ, a technique capable of providing information on the existence and the localization of repetitive DNA along the chromosome axis (Mezzanotte et al., 1983a, b; Lopez Fernandez et al., 1991). The karyotypes of seven A. rostrata individuals (three males and four females) from North America were analysed. Sex was determined by histological analysis of gonads and species were identified by vertebral counts. Metaphase chromosomes were obtained from lymphocyte cultures, according to Cau et al. (1988), and the experiments with REs were carried out according to Cau et al. (1992). Slides were stained in 25% Wright's stain (in 0.06 M phosphate buffer, pH 6.8) for 8 min, briefly rinsed in distilled water and air-dried. AluI produces a pattern resembling C-banding which tends to disappear when incubation is carried out for >3 h, in fact, after overnight incubation it produces relatively uniform faint staining in all chromosomes [Fig. 1(a)].
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