Reconstruction of a 450 MY-old Ancestral Vertebrate Proto-karyotype
From recent work the putative eutherian karyotype from 100 MYA has been derived. Here, we have applied a new in silico technique, termed electronic chromosome painting (E-painting) on a large dataset of genes whose chromosome assignments are known in human, chicken, zebrafish and pufferfish. By E-painting conserved syntenies are identified in whatever direction, back and reverse, is wanted. In a first step, from human and chicken data the ancestral tetrapod proto-karyotype from about 310 MYA was reconstructed. This karyotype reveals most of the chromosome characteristics already basic for the reconstruction of the eutherian proto-karyotype and consists of 18 chromosome pairs. Second, from the zebrafish and pufferfish data a proto-teleost karyotype prior to the extra whole genome duplication specific for the teleost fish with 12 chromosome pairs was built. Also this proto-karyotype is already about 300 MY old. From both these reconstructions it was possible to deduce the vertebrate proto-karyotype from 450 MYA. This karyotype is made up of 11 proto-chromosome pairs. The extraordinary conservation of the vertebrate genome is apparent. It is evident that during karyotype evolution in land-vertebrates interchromosomal rearrangements by translocation are relatively frequent whereas the karyotypes of birds and fish are much more conserved. By comparing all vertebrates the human karyotype, which proved to be one of the most conserved in eutherians, can no longer be considered to be highly conserved. Only four human chromosomes (9, 11, 14, 18) appear highly conserved, each representing a single segment of an ancestral proto-chromosome.