Nads

NADs, in genomic contexts, stands for nucleolus-associated domains, a class of chromatin regions that physically associate with the nucleolus. They are identified through genome-wide mapping of chromatin interactions with the nucleolus using methods such as DamID and sequencing of nucleolus-associated chromatin.

NADs tend to be gene-poor and enriched for repetitive elements and satellite DNA. They are typically marked by repressive histone modifications such as H3K9me3 and show late replication timing and low transcriptional activity. Their association with the nucleolus is thought to contribute to a repressive nuclear microenvironment and to the organization of heterochromatin.

The presence of NADs is not uniform across the genome; instead, NADs exhibit cell-type specific and dynamic patterns. They can reorganize during differentiation, aging, or in response to cellular stress. Their positioning relative to the nucleolus can influence the silencing of resident genes and interact with other nuclear subcompartments to shape overall genome architecture.

Research into NADs emphasizes their role in genome organization, transcriptional regulation, and genome stability. Alterations in NAD patterns have been observed in certain cancers and during cellular aging, suggesting potential links to phenotypic change and disease, though the mechanisms remain under investigation.

In related discussions, NADs are distinguished from lamina-associated domains (LADs), which localize to the nuclear lamina. The acronym NAD can also refer to nicotinamide adenine dinucleotide in other contexts, but NADs specifically denotes nucleolus-associated domains in this usage.