Cajal bodies (CBs) are spherical sub-organelles of 0.3-1.0 µm in diameter found in the
nucleus of proliferative
cells like
embryonic cells and
tumor cells, or metabolically active cells like
neurons. In contrast to cytoplasmic
organelles, CBs lack any phospholipid membrane which would separate their content, largely consisting of proteins and RNA, from the surrounding
nucleoplasm. They were first reported by
Santiago Ramón y Cajal in 1903, who called them
nucleolar accessory bodies due to their association with the
nucleoli in neuronal cells. They were rediscovered by electron microscopists and named coiled bodies, according to their appearance as coiled threads on
EM images, and later renamed after their discoverer. Research on CBs was accelerated after discovery and
cloning of the marker protein
p80/Coilin. CBs have been implicated in RNA-related metabolic processes such as
snRNPs biogenesis, maturation and recycling,
histone mRNA processing and telomere maintenance. CBs assemble RNA which is used by telomerase to add nucleotides to the ends of telomeres.