macrosatellite

Macrosatellite is a term used in genomics to describe a class of very large tandemly repeated DNA sequences. Each macrosatellite consists of a repeat unit that is typically hundreds to thousands of base pairs in length, arranged in long arrays that can span from several hundred kilobases to multiple megabases. The repeats are usually located in pericentromeric or subtelomeric regions and are enriched for heterochromatin. Copy number of macrosatellites varies considerably among individuals and populations, and the repetitive nature of the arrays makes them difficult to characterize with standard short-read sequencing.

The best-characterized macrosatellite is the D4Z4 array on chromosome 4q35, where the number of repeats affects chromatin structure and gene expression; contraction of the array is associated with facioscapulohumeral muscular dystrophy type 1. Other macrosatellites, such as DXZ4 on the X chromosome, have been studied for roles in chromatin organization and regulation of X-chromosome inactivation. Although most macrosatellites are not coding, they can be transcribed to noncoding RNAs and may influence genome architecture.

Technological approaches for studying macrosatellites include Southern blot, pulsed-field gel electrophoresis, and long-read sequencing to resolve large arrays. Epigenetic marks, such as DNA methylation, are also analyzed to understand their functional state. In population genetics, macro repeats are considered highly dynamic and subject to rapid structural variation.

Macrosatellites are distinct from microsatellites and minisatellites by unit length and total size, but share the general feature of being tandemly repeated DNA with potential structural or regulatory roles.