Polar Biol (1994) 14:285-290 Springer-Verlag 1994 T. Capriglione. A. Morescalchi E. Olmo- L. Rocco V. Stingo S. Manzo Satellite DNAs, Heterochromatin and sex chromosomes in Chionodraco hamatus (Channichthyidae, Percif0rmes) Received: 11 June 1993/Accepted: 14 November 1993 Abstract We studied the genome of an antarctic ice fish, Chionodraco hamatus, in order to detect highly repetitive DNAs that may play a role in hetero- chromatinization processes and sex chromosome differ- entiation. We used two different experimental approaches. Hybridization of a Bkm probe to genomic DNA showed slight differences between the two sexes. Using restriction enzymes, a Bgl II satellite (pIF) was isolated. In situ hybridization revealed a preferential localization of pIF on the centromeres and the telomeres of most chromosomes, as well as an inter- stitial band on the long arms of the neo-Y sex chromo- some, where probably the hypothetical fusion took place. Dot-blot experiments showed that pIF is still present in species belonging to different families of the same suborder. Though preliminary, our results suggest a conservative nature of this DNA which might have played a definite functional role in the genome of these polar fishes. Introduction It has been suggested that highly repetitive DNAs local- ized in heterochromatic areas may play a relevant role in several chromosome mutations, such as hetero- chromatinization processes (Ng et al. 1986; Radic et al. 1987), Robertsonian rearrangements (Mayr et al. 1984) and sex-chromosome differentiation (Jones 1984). T. Capriglione L. Rocco V. Stingo S. Manzo Dipartimento di Biologia Evolutiva e Comparata, Via Mezzocannone 8, 1-80134 Napoli, Italy E. Olmo Istituto di Biologia e Genetica, Via delle Brecce Bianche, 1-60100 Ancona, Italy A. Morescalchi (~) Istituto di Anatomia Comparata, Viale Benedetto XV, 5, 1-16132, Genova, Italy In particular, a satellite DNA, named Bkm and pref- erentially located on the W chromosome, has been isolated from some species of snakes by Jones and Singh (Singh et al. 1980); they suggested that sexchromosome differentiation may depend on the preferential accumu- lation of these DNA sequences on either sex homolog, accompanied by wide heterochromatinization of this chromosome (Jones 1984). The studies so far conducted in several organisms have shown quite a controversial situation. In some species, Bkm is preferentially distrib- uted in the heterogametic sex, being localized mainly or exclusively either on the W or the Y chromosome (Jones 1984; Schafer et al. 1986; Nanda et al. 1990). Vice versa, in other species, this DNA is absent or, if any, does not show either a sex-specific distribution or any relations with sex chromosomes (Arnemann et al. 1986; Traut 1987; Miklos et al. 1989; Pelliccia et al. 1991). In some other species, instead, highly repetitive DNAs have been found, which have a preferential distribution in the heterogametic sex, but do not show any affinity with or resemblance to Bkm (Griffith and Holland 1990; Tone et al. 1984). Sex-chromosome differentiation associated with het- erochromatization processes have been evidenced also in teleosteans (Galetti and Foresti 1986; Haaf and Schmid 1984). However, DNA-to-DNA hybridization studies, using Bkm-like oligonucleotides, have shown a controversial and variable situation also in these verte- brates, including species with a sex-specific distribution of this DNA and species where there are no differences between the two sexes (Nanda et al. 1990, 1992). An interesting system of multiple sex chromosomes has been found in Antarctic fishes of the suborder notothenioids. In these teleosteans, the Y chromosome would have originated by tandem or Robertsonian fusion (Morescalchi et al. 1991); it is characterized by the presence of C-banded heterochromatin in the sup- posed areas of fusion (Morescalchi et al. 1992). Based on these morphological data, we undertook a study in order to get a deeper insight into the genetic