Chromosome Diversification in Antarctic Fish (Notothenioidei)
283
Molecular Cytogenetics and Future Studies
The technology now exists which will permit major advances in genetics
and cytogenetics of fishes (and Antarctic fishes) at the molecular level. One
promising molecular cytogenetic method with broad application is
fluorescence in situ hybridization (FISH) [26]. This technique has been
widely used in human genetics to identify chromosomes and to localize
genes on the chromosome arms [27]. Recent results using FISH have
resolved the problem of species chromosome homology between many
mammals and has defined the chromosomal syntenies and major
translocations involved in the genome evolution of higher vertebrates,
especially primates [28]. Genomic specific sequences corresponding to
highly repetitive ribosomal genes (rDNAs) were obtained from Antarctic
fish and then used as a probe to map the chromosome location of the 28S
rDNA in Champsocephalus gunnari using FISH. The structural
information derived has implication for general knowledge of the genome
in teleosts [8]. Using similar methods a satellite DNA was isolated from
Chionodraco hamatus and mapped to that species' chromosomes. The
interstitial location of this satellite in the Y-chromosome supports the
hypothesis about the origin of the sex-linked heteromorphic chromosomes
in this species [29]. Specific centromeric and telomeric probes could be
used to examine intraspecific chromosome rearrangements and painting
with chromosome probes could also be used to assess intraspecific
homologies and to provide unambiguous mapping information. Such
advances would overcome many of the limits of conventional karyotyping
for phylogenetic analysis. Moreover information on chromosome changes
in various species would help to test more general assumptions regarding
the role of chromosomes in speciation and evolution [11,30].
Finally, various molecular cytogenetic techniques are now available
which permit the visualization of smaller DNA sequences and even single
genes directly on chromosomes, in interphase nuclei or on stretched DNA
filaments. These methods would allow the mapping of genes important in
the diversification and adaptation of the Antarctic species such as globin or
antifreeze protein genes. Such information would provide new perspective
on understanding how changes in genome organization and function are
correlated with critical events in the evolution of Antarctic fish.
Acknowledgments
The Italian National Programme for Antarctic Research, the Institut Fran9ais pour
la Recherche et la Technologie Polaire, the Australian Antarctic Division, the
CNRS GDR 1005 and the Museum National d'Histoire Naturelle of Paris provided
financial support. The European Science Foundation Network "Fishes of the
Antarctic Ocean" also supported both collaborative exchanges and field work. R.
283
Molecular Cytogenetics and Future Studies
The technology now exists which will permit major advances in genetics
and cytogenetics of fishes (and Antarctic fishes) at the molecular level. One
promising molecular cytogenetic method with broad application is
fluorescence in situ hybridization (FISH) [26]. This technique has been
widely used in human genetics to identify chromosomes and to localize
genes on the chromosome arms [27]. Recent results using FISH have
resolved the problem of species chromosome homology between many
mammals and has defined the chromosomal syntenies and major
translocations involved in the genome evolution of higher vertebrates,
especially primates [28]. Genomic specific sequences corresponding to
highly repetitive ribosomal genes (rDNAs) were obtained from Antarctic
fish and then used as a probe to map the chromosome location of the 28S
rDNA in Champsocephalus gunnari using FISH. The structural
information derived has implication for general knowledge of the genome
in teleosts [8]. Using similar methods a satellite DNA was isolated from
Chionodraco hamatus and mapped to that species' chromosomes. The
interstitial location of this satellite in the Y-chromosome supports the
hypothesis about the origin of the sex-linked heteromorphic chromosomes
in this species [29]. Specific centromeric and telomeric probes could be
used to examine intraspecific chromosome rearrangements and painting
with chromosome probes could also be used to assess intraspecific
homologies and to provide unambiguous mapping information. Such
advances would overcome many of the limits of conventional karyotyping
for phylogenetic analysis. Moreover information on chromosome changes
in various species would help to test more general assumptions regarding
the role of chromosomes in speciation and evolution [11,30].
Finally, various molecular cytogenetic techniques are now available
which permit the visualization of smaller DNA sequences and even single
genes directly on chromosomes, in interphase nuclei or on stretched DNA
filaments. These methods would allow the mapping of genes important in
the diversification and adaptation of the Antarctic species such as globin or
antifreeze protein genes. Such information would provide new perspective
on understanding how changes in genome organization and function are
correlated with critical events in the evolution of Antarctic fish.
Acknowledgments
The Italian National Programme for Antarctic Research, the Institut Fran9ais pour
la Recherche et la Technologie Polaire, the Australian Antarctic Division, the
CNRS GDR 1005 and the Museum National d'Histoire Naturelle of Paris provided
financial support. The European Science Foundation Network "Fishes of the
Antarctic Ocean" also supported both collaborative exchanges and field work. R.