A basal body (synonymous with basal granule, kinetosome, and in older cytological literature with blepharoplast) is a protein structure found at the base of a
eukaryotic
Eukaryotes () are organisms whose cells have a nucleus. All animals, plants, fungi, and many unicellular organisms, are Eukaryotes. They belong to the group of organisms Eukaryota or Eukarya, which is one of the three domains of life. Bact ...
undulipodium (
cilium or
flagellum). The basal body was named by
Theodor Wilhelm Engelmann in 1880 It is formed from a
centriole and several additional protein structures, and is, essentially, a modified centriole.
The basal body serves as a nucleation site for the growth of the
axoneme microtubules. Centrioles, from which basal bodies are derived, act as anchoring sites for proteins that in turn anchor
microtubules, and are known as the
microtubule organizing center (MTOC). These microtubules provide structure and facilitate movement of vesicles and organelles within many eukaryotic cells.
Assembly, structure
Cilia and basal bodies form during quiescence or the
G1 phase of the
cell cycle
The cell cycle, or cell-division cycle, is the series of events that take place in a cell that cause it to divide into two daughter cells. These events include the duplication of its DNA ( DNA replication) and some of its organelles, and sub ...
. Before the cell enters G1 phase, i.e. before the formation of the cilium, the mother centriole serves as a component of the
centrosome
In cell biology, the centrosome (Latin centrum 'center' + Greek sōma 'body') (archaically cytocentre) is an organelle that serves as the main microtubule organizing center (MTOC) of the animal cell, as well as a regulator of cell-cycle pro ...
.
In cells that are destined to have only one primary cilium, the mother centriole differentiates into the basal body upon entry into G1 or quiescence. Thus, the basal body in such a cell is derived from the centriole.
The basal body differs from the mother centriole in at least 2 aspects. First, basal bodies have basal feet, which are anchored to cytoplasmic microtubules and are necessary for polarized alignment of the cilium. Second, basal bodies have pinwheel-shaped transition fibers that originate from the appendages of mother centriole.
In multiciliated cells, however, in many cases basal bodies are not made from centrioles but are generated ''de novo'' from a special protein structure called the
deuterosome.
Function
During cell cycle quiescence, basal bodies organize primary cilia and reside at the cell cortex in proximity to plasma membrane. On cell cycle entry, cilia resorb and the basal body migrates to the nucleus where it functions to organize centrosomes. Centrioles, basal bodies, and cilia are important for mitosis, polarity, cell division, protein trafficking, signaling, motility and sensation.
Mutations in proteins that localize to basal bodies are associated with several human ciliary diseases, including
Bardet–Biedl syndrome,
orofaciodigital syndrome,
Joubert syndrome,
cone-rod dystrophy,
Meckel syndrome, and
nephronophthisis.
Regulation of basal body production and spatial orientation is a function of the nucleotide-binding
domain of
γ-tubulin.
Plants lack centrioles and only lower plants (such as mosses and ferns) with motile sperm have flagella and basal bodies.
[Philip E. Pack, Ph.D., Cliff's Notes: AP Biology 4th edition.]
References
External links
* - "Ultrastructure of the Cell: ciliated epithelium, cilia and basal bodies"
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Organelles