Chromosome painting reveals that galagos have highly derived karyotypes.

The differences in chromosome number between Otolemur crassicaudatus (2n = 62) and Galago moholi (2n = 38) are dramatic. However, the total number of signals given by hybridizing human chromosome paints to galago metaphases is similar: 42 in O. crassicaudatus and 38 G. moholi. Many human chromosome homologs are found fragmented in each species, and numerous translocations have resulted in chromosomal syntenies or hybridization associations which differ from those found in humans. Only 7 human autosomes showed conserved synteny in O. crassicaudatus, and 9 in G. moholi. Both galago species have numerous associations or syntenies not found in humans: O. crassicaudatus has 11, and G. moholi has 21. The phylogenetic line leading to the last common ancestor of the two galago species accumulated 6 synapomorphic fissions and 5 synapomorphic fusions. Since the divergence of the two galago species, 10 Robertsonian translocations have further transformed the G. moholi karyotype, and 2 fissions have been incorporated into the O. crassicaudatus karyotype. Comparison with other primates, tree shrews, and other mammals shows that both galagos have karyotypes which are a mixture of derived and conserved chromosomes, and neither has a karyotype close to that of the proposed ancestor of all primates. Am J Phys Anthropol 117:319-326, 2002. Published 2002 Wiley-Liss, Inc.

Chromosome painting defines genomic rearrangements between red howler monkey subspecies.

We hybridized whole human chromosome-specific DNA libraries to chromosomes of two supposed subspecies of Alouatta seniculus: Alouatta seniculus sara and Alouatta seniculus arctoides. The number of hybridization signals per haploid set is 42 in A. s. sara and 43 in A. s. arctoidea; the two karyotypes differ by at least 16 chromosomal rearrangements, including numerous translocations. An unusual sex chromosome system is shared by both taxa. The sex chromosome system results from a Y translocation with a chromosome homologous to parts of human chromosome 3/15 and can be described as X1X2Y1Y2/X1X1X2X2 (male/female). Both red howlers also have microchromosomes, a highly unusual karyological trait not found in other higher primates. These microchromosomes are not hybridized by any human chromosome paint and therefore are probably composed of repetitive DNA. It is well known that New World monkeys have high karyological variability. It is probable that molecular cytogenetic analyses including chromosome painting will permit an accurate reconstruction of the phylogeny of these monkeys and help establish the ancestral karyotype for higher primates.

Mapping chromosomal homology between humans and the black-handed spider monkey by fluorescence in situ hybridization.

We hybridized human chromosome-specific DNA probes to metaphases of the New World monkey Ateles geoffroyi to map the chromosomal homology between these two species. In the haploid Ateles geoffroyi karyotype the total number of signals was 51 for the 22 human autosomal probes used. Compared with Old World monkeys, the number of translocations found in the black-handed spider monkey karyotype was quite striking. The majority of these translocations are apparently Robertsonian and no reciprocal translocations were revealed. Nine autosomal human chromosome probes (11, 13, 14, 17, 18, 19, 20, 21, 22) provided only two signals each per metaphase, but six of these were translocated to subregions of different spider monkey chromosomes. The other 13 autosomal human chromosome paints (1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 15, 16) provided fragmented signals. Three human probes (5, 8, 10) provided signals located on two pairs of spider monkey chromosomes. Four human paints (2, 3, 4, 12) provided hybridization signals on three pairs of chromosomes. Probes 6, 7, 15 provided six signals each on two pairs of chromosomes; probe 16 gave eight signals on two pairs of spider monkey chromosomes and probe 1 gave 12 signals on four pairs of chromosomes. The synteny between segments to human 18/8 appears to be an apomorphic ancestral condition for all New World monkeys. A synteny between regions homologous to human 16/10, 5/7 and 2/16 HSA is probably an apomorphic ancestral condition for all Cebidae. The syntenic association 3/15 and 4/1 is an apomorphic condition for the Atelinae.

Fluorescence in situ hybridization (FISH) maps chromosomal homologies between the dusky titi and squirrel monkey.

The Platyrrhini are one of the most karyologically derived groups of primates and the evolution of their karyotypes is far from understood. The identification of the origin and direction of chromosome rearrangements will contribute to a better understanding of New World monkey phylogeny, taxonomy, and evolution. We mapped homology and identified translocations in the chromosomes of the dusky titi monkey (Callicebus moloch, 2n = 50) and the squirrel monkey (Saimiri sciureus, 2n = 44) by fluorescence in situ hybridization (FISH) of human chromosome paints. The hybridization results established chromosomal homologies between these New World primates, humans, other primates, and more distantly related mammalian species and show that both species have highly rearranged karyotypes. The total number of hybridization signals was 37 in C. moloch and 40 in S. sciureus, which is in the range of most comparisons of human chromosomes with phylogenetically more distant species outside of the primate order. Parsimony analyses of outgroup painting patterns allowed us to propose an ancestral karyotype for New World monkeys consisting of 2n = 56 with homologs to the following human chromosomes or chromosome segments: 1b; 1c; 2a; 2b; 3a; 3b; 3/21; 4; 5; 6; 7; 8a; 8/18; 9; 10a; 10/16; 11; 12; 13; 14/15; 15a; 16a; 17; 19; 20; 22; X; Y. Associations 8/18 and 10/16 are derived ancestral associations for all Platyrrhini. A 2/16 association found in S. sciureus and C. moloch was also seen in Ateles geoffroyi and Cebus capucinus; a 5/7 association in S. sciureus was present in A. geoffroyi, C. capucinus, and Alouatta belzebul. Other associations seen in the dusky titi monkey or the squirrel monkey are probably automorphisms. Comparison with chromosome phylogenies based on R-banding [Dutrillaux et al., 1986] showed that there were many errors in assigning homology with human chromosomes. The chromosomal phylogeny of New World monkeys based on banding patterns is in need of revision using modern molecular methods.

In situ hybridization (FISH) maps chromosomal homologies between Alouatta belzebul (Platyrrhini, Cebidae) and other primates and reveals extensive interchromosomal rearrangements between howler monkey genomes.

We hybridized whole human chromosome specific probes to metaphases of the black-and-red howler monkey Alouatta belzebul in order to establish chromosomal homology between humans and black-and-red howlers. The results show that the black-and-red howler monkey has a highly rearranged genome and that the human chromosome homologs are often fragmented and translocated. The number of hybridization signals we obtained per haploid set was 40. Nine human chromosome probes gave multiple signals on different howler chromosomes, showing that their synteny is disturbed in A. belzebul. Fourteen black-and-red howler autosomes were completely hybridized by one human autosomal paint, six had two signals, three had three signals, and one chromosome had four signals. Howler chromosomes with multiple signals have produced 12 chromosomal syntenies or hybridization associations which differ from those found in humans: 1/2, 2/20, 3/21, 4/15, 4/16, 5/7, 5/11, 8/18, 9/12, 10/16, 14/15, and 15/22. The hybridization pattern was then compared with those found in two red howler taxa and other mammals. The comparison shows that even within the genus Alouatta numerous interchromosomal rearrangements differentiate each taxa: A. belzebul has six unique apomorphic associations, A. seniculus sara and A. seniculus arctoidea share seven derived associations, and additionally A. seniculus sara has four apomorphic associations and A. seniculus arctoidea seven apomorphic associations. A. belzebul appears to have a more conserved karyotype than the red howlers. Both red and black-and-red howlers are characterized by Y-autosome translocations; the peculiar chromosomal sex system found in the red howler taxa could be considered a further transformation of the A. belzebul sex system. The finding that apparently morphologically similar or even identical taxa have such extreme genomic differences has important implications for speciation theory and neotropical primate conservation.

Reciprocal chromosome painting between a New World primate, the woolly monkey, and humans.

We employed fluorescence-activated chromosome sorting (FACS) to construct chromosome paint sets for the woolly monkey (Lagothrix lagotricha) and then FISH to reciprocally paint human and woolly monkey metaphases. Reciprocal chromosome painting between humans and the woolly monkey allowed us to assign subchromosomal homologies between these species. The reciprocal painting data between humans and the woolly monkey also allow a better interpretation of the chromosomal difference between humans and platyrrhines, and refine hypotheses about the genomic rearrangements that gave origin to the genome of New World monkeys. Paints of woolly monkey chromosomes were used to paint human metaphases and forty-five clear signals were detected. Paints specific to each human chromosome were used to paint woolly monkey metaphases. The 23 human paints gave 39 clear signals on the woolly monkey karyotype. The woolly monkey chromosomes painted by human paints produced 7 associations of segments homologous to human chromosomes or human chromosome segments: 2/16, 3/21, 4/15, 5/7, 8/18, 10/16 and 14/15. A derived translocation between segments homologous to human chromosomes 4 and 15 is a synapomorphic marker linking all Atelines. These species may also be linked by fragmentation of homologs to human 1, 4, and 15.