Evolution of Alpha‐Satellite DNA

Đurđica Ugarković, Ruđer Bošković Institute, Zagreb, Croatia

Published online: February 2013

DOI: 10.1002/9780470015902.a0020829.pub2

Full Article on Wiley Online Library

Alpha satellite deoxyribonucleic acid (DNA) is based on 171 bp tandem repeats located in the centromeric and pericentromeric regions of all primate chromosomes. In humans, most of the alpha satellite repeats are organised in a hierarchical fashion, creating complex units called higher order repeats, composed of 2 to more than 30 diverged monomers in length. Monomeric alpha satellite DNA predates higher order arrays of alpha satellite and may represent direct descendant of the ancestral primate centromere sequence. Comparison of centromeric alpha satellite DNA sequences in different primate species reveals that alpha satellite DNA evolves through a series of amplification events resulting in the spreading of ‘new’ subfamilies, which replace the ‘old’ ones and confer centromere function. Transcripts of alpha satellite play an important role in kinetochore formation and the establishment of pericentromeric heterochromatin and are indispensable for the proper cell division.

Key Concepts:

Complex higher order repeats (HORs) are predominant form of alpha satellite DNA in the great ape and humans.
Alpha satellite HORs evolve much faster than monomers and contribute substantially to divergence between chromosomes of primates.
Two distinct chromosomal domains, the centromere and heterochromatin are assembled and maintained on the alpha satellite DNA sequence.
Alpha satellite DNA evolves through proximal amplification events occurring within the central active region of the centromere.
Transcription of alpha satellite DNA is crucial for centromere/kinetochore assembly and function during cell division.

Keywords: alpha satellite DNA; higher order repeats; centromere; heterochromatin; concerted evolution

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Article Title:	Evolution of Alpha‐Satellite DNA
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	Figure 1. Long monomers (171 bp) of alpha satellite DNA in great ape are organised in a hierarchical fashion, creating complex repeating units called HORs. HORs represent multimers composed of 2–30 diverged alpha satellite monomers. HORs are further tandemly repeated forming alpha satellite array.
	Figure 2. Organisation of alpha satellite DNA within centromeric and pericentromeric region of human X chromosome based on data from Schueler et al. (2005). DXZ1 region of 3 Mb, in which primary constriction is located, is composed of tandemly repeated HORs. HORs are mutually highly homologous exhibiting 1–2% divergence. DXZ1 array is flanked on both sites by a region of approximate size of 450 kb, which is composed mostly of alpha satellite monomers. Alpha satellite monomers within 450 kb array exhibit divergence between 20% and 30% and are interspersed with transposable elements such as LINE and SINE. HORs participate in kinetochore formation, whereas diverged monomers contribute to heterochromatin establishment. Phylogenetic analysis resolves alpha satellite monomers within 450 kb region into four subfamilies, whereas monomers within DXZ1 array form distinct, fifth alpha satellite subfamily. Adjacent to 450 kb region is euchromatic DNA.
	Figure 3. Model of evolution of alpha satellite DNA centromeric region from the ancestral primate to humans. The series of amplification events are responsible for the spreading of ‘new’ alpha satellite subfamilies and replacement of ‘old’ ones, which, however, remain preserved in genome in lower number of copies (differently dashed rectangles). The ‘old’ subfamilies are based on tandemly repeated monomers, but the most recently amplified subfamily is based on tandemly repeated HORs. This subfamily comprises centromeric regions in humans and other great apes. The model is based on the data on human X chromosome centromere structure (Schueler et al., 2005).

Evolution of Alpha‐Satellite DNA

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