hrvatski

Are noncoding DNA sequences responsible for speciation?

Heterochromatic chromosomal segments differ from their euchromatic counterparts by a number of peculiar molecular characteristics, such as high level of chromatin condensation throughout the cell cycle, late DNA replication, and paucity of genes. However, functions vital for chromosomes, those of centromeres and telomeres, are embedded within heterochromatin. Major DNA components of centromeric heterochromatin are non-coding tandemly repeated sequences, or satellite DNAs. While centromeric function is conserved in evolution, DNA components are not, and composition of centromeric satellites differs often even between closely related organisms. Recent experiments have provided evidence that related species share a collection, or a library, of satellite sequences that coexist in centromeric heterochromatin, but differ significantly in a copy number. Species– specific satellite DNA profiles result from amplification of a particular satellite into a major, highly abundant satellite DNA, while the others are still present as minor repeats. Nucleotide changes of satellite sequences occur within a broad variety of rates, thus contributing to the genesis of species– specific satellite profiles. In addition, rearrangements and amplifications of preexisting sequences lead to generation of novel satellite repeating units. Differences among major satellite components of centromeric heterochromatin could disable regular chromosome pairing and disjunction in hybrids. Changes in major satellite DNAs are followed by changes in corresponding centromeric histones, as demonstrated by Henikoff and coworkers. Both effects could reflect on the fecundity in crosses between individuals, thus raising a reproductive barrier that would ultimately act as a trigger in the speciation process.

satellite DNA; heterochromatin; centromere; simpatric speciation

nije evidentirano

engleski

Are noncoding DNA sequences responsible for speciation?

Heterochromatic chromosomal segments differ from their euchromatic counterparts by a number of peculiar molecular characteristics, such as high level of chromatin condensation throughout the cell cycle, late DNA replication, and paucity of genes. However, functions vital for chromosomes, those of centromeres and telomeres, are embedded within heterochromatin. Major DNA components of centromeric heterochromatin are non-coding tandemly repeated sequences, or satellite DNAs. While centromeric function is conserved in evolution, DNA components are not, and composition of centromeric satellites differs often even between closely related organisms. Recent experiments have provided evidence that related species share a collection, or a library, of satellite sequences that coexist in centromeric heterochromatin, but differ significantly in a copy number. Species– specific satellite DNA profiles result from amplification of a particular satellite into a major, highly abundant satellite DNA, while the others are still present as minor repeats. Nucleotide changes of satellite sequences occur within a broad variety of rates, thus contributing to the genesis of species– specific satellite profiles. In addition, rearrangements and amplifications of preexisting sequences lead to generation of novel satellite repeating units. Differences among major satellite components of centromeric heterochromatin could disable regular chromosome pairing and disjunction in hybrids. Changes in major satellite DNAs are followed by changes in corresponding centromeric histones, as demonstrated by Henikoff and coworkers. Both effects could reflect on the fecundity in crosses between individuals, thus raising a reproductive barrier that would ultimately act as a trigger in the speciation process.

satellite DNA; heterochromatin; centromere; simpatric speciation

nije evidentirano