The genomic sequence for Prader-Willi/Angelman syndromes' loci of human is apparently conserved in the great apes

Refinement of a chimpanzee pericentric inversion breakpoint to a segmental duplication cluster

BACKGROUND

Pericentric inversions are the most common euchromatic chromosomal differences among humans and the great apes. The human and chimpanzee karyotype differs by nine such events, in addition to several constitutive heterochromatic increases and one chromosomal fusion event. Reproductive isolation and subsequent speciation are thought to be the potential result of pericentric inversions, as reproductive boundaries form as a result of hybrid sterility.

RESULTS

Here we employed a comparative fluorescence in situ hybridization approach, using probes selected from a combination of physical mapping, genomic sequence, and segmental duplication analyses to narrow the breakpoint interval of a pericentric inversion in chimpanzee involving the orthologous human 15q11-q13 region. We have refined the inversion breakpoint of this chimpanzee-specific rearrangement to a 600 kilobase (kb) interval of the human genome consisting of entirely duplicated material. Detailed analysis of the underlying sequence indicated that this region comprises multiple segmental duplications, including a previously characterized duplication of the alpha7 neuronal nicotinic acetylcholine receptor subunit gene (CHRNA7) in 15q13.3 and several Golgin-linked-to-PML, or LCR15, duplications.

CONCLUSIONS

We conclude that, on the basis of experimental data excluding the CHRNA7 duplicon as the site of inversion, and sequence analysis of regional duplications, the most likely rearrangement site is within a GLP/LCR15 duplicon. This study further exemplifies the genomic plasticity due to the presence of segmental duplications and highlights their importance for a complete understanding of genome evolution.

Evolutionary divergence of the oncogenes GLI, HST and INT2

Almost a quarter of a century ago, the banding patterns of human and other higher primate chromosomes were compared, creating a barrage of speculation. Consequently, a number of approaches have been used to understand human descent. Chromosome modifications are believed to be important in the origin of species, and pericentric inversions account for the majority of evolutionary chromosomal alterations seen in Hominoidea. A comparative mapping fluorescence in situ hybridization technique, using locus-specific DNA probes as phylogenotic markers, was used to decipher the pericentric inversions of human chromosomes 11 and 12. Human-derived (Homo sapiens, HSA) DNA probes for GLI, HST and INT2 protooncogenes were used to identify their homologous locations in the chromosomes of chimpanzee (Pan troglodytes, PTR), gorilla (Gorilla gorilla, GGO) and orangutan (Pongo pygmaeus, PPY). The INT2 and HST loci mapping results confirm the earlier putative claim that a pericentric inversion took place in HSA chromosome 11 and its equivalent PTR and GGO chromosomes. In addition, these data provide additional information regarding the orangutan's position on the evolutionary tree of Pongidae and Hominidae. GLI mapping reveals that a pericentric inversion occurred in the HSA chromosome 12 equivalent in PTR and GGO, but was not seen in HSA or PPY. These pericentric inversions in PTR and GGO may have occurred at a period when both PTR and GGO had branched off from the Hominoidae trunk. The use of loci-specific probes to decipher pericentric inversions has proved to be a formidable approach in characterizing chromosome rearrangements and providing further evidence on human descent.

Brief communication: comparative mapping of the human estrogen receptor (ESR) and the Kallmann (KAL) regions to the chromosomes of the great apes

Human and great ape chromosomes display significant concordance by molecular and cytogenetic techniques, which may reflect their common origin. Nevertheless, chromosomal banding techniques did not reflect the syntenic homology at the DNA level, which created controversy and debate. The recent availability of the unique sequence loci-specific human estrogen receptor (ESR) (bq25.1) region and Kallmann (KAL) (Xp22.3) DNA probes have prompted us to search the degree of DNA sequence synteny among chimpanzee, gorilla, and orangutan by the FISH technique. The conservation of the ESR and Kallmann regions at the corresponding equivalent loci of the great ape chromosomes (5q25 and Xp22, respectively) has provided insights into genome evolution and facilitated assignment of map locations for human unique DNA sequences. These findings are aimed toward developing an augmented framework to determine with greater certainty the pathway of human descent at the single gene level.

A unique genomic sequence in the Wolf-Hirschhorn syndrome [WHS] region of humans is conserved in the great apes

The Wolf-Hirschhorn syndrome (WHS) is caused by a partial deletion in the short arm of chromosome 4 band 16.3 (4p 16.3). A unique-sequence human DNA probe (39 kb) localized within this region has been used to search for sequence homology in the apes' equivalent chromosome 3 by FISH-technique. The WHS loci are conserved in higher primates at the expected position. Nevertheless, a control probe, which detects alphoid sequences of the pericentromeric region of humans, is diverged in chimpanzee, gorilla, and orangutan. The conservation of WHS loci and divergence of DNA alphoid sequences have further added to the controversy concerning human descent.