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In cell biology a centriole is a cylindrical organelle composed mainly of a protein called tubulin. Centrioles are found in most eukaryotic cells, but are not present in conifers (Pinophyta), flowering plants (angiosperms) and most fungi, and are only present in the male gametes of charophytes, bryophytes, seedless vascular plants, cycads, and Ginkgo. A bound pair of centrioles, surrounded by a highly ordered mass of dense material, called the pericentriolar material (PCM), makes up a structure called a centrosome.
A flagellum is a hairlike appendage that protrudes from a wide range of microorganisms termed as flagellates. A flagellate can have one or several flagella. Certain other cells are flagellated, such as the mammalian sperm cell, which uses its flagellum to propel itself through the female reproductive tract. The primary function of a flagellum is that of motility. In some bacteria the flagellum can also function as a sensory organelle, being sensitive to wetness, chemicals, and temperatures outside the cell.
The cilium is an organelle found on eukaryotic cells in the shape of a slender protuberance that projects from the much larger cell body.
The evolution of flagella is of great interest to biologists because the three known varieties of flagella each represent a sophisticated cellular structure that requires the interaction of many different systems.
The microtubule-organizing center (MTOC) is a structure found in eukaryotic cells from which microtubules emerge. MTOCs have two main functions: the organization of eukaryotic flagella and cilia and the organization of the mitotic and meiotic spindle apparatus, which separate the chromosomes during cell division. The MTOC is a major site of microtubule nucleation and can be visualized in cells by immunohistochemical detection of γ-tubulin. The morphological characteristics of MTOCs vary between the different phyla and kingdoms. In animals, the two most important types of MTOCs are 1) the basal bodies associated with cilia and flagella and 2) the centrosome associated with spindle formation.
Spermatogenesis is the process by which haploid spermatozoa develop from germ cells in the seminiferous tubules of the testis. This process starts with the mitotic division of the stem cells located close to the basement membrane of the tubules. These cells are called spermatogonial stem cells. The mitotic division of these produces two types of cells. Type A cells replenish the stem cells, and type B cells differentiate into primary spermatocytes. The primary spermatocyte divides meiotically into two secondary spermatocytes; each secondary spermatocyte divides into two equal haploid spermatids by Meiosis II. The spermatids are transformed into spermatozoa (sperm) by the process of spermiogenesis. These develop into mature spermatozoa, also known as sperm cells. Thus, the primary spermatocyte gives rise to two cells, the secondary spermatocytes, and the two secondary spermatocytes by their subdivision produce four spermatozoa and four haploid cells.
Primary ciliary dyskinesia (PCD), is a rare, ciliopathic, autosomal recessive genetic disorder that causes defects in the action of cilia lining the respiratory tract, fallopian tube, and flagellum of sperm cells. The phrase "immotile ciliary syndrome" is no longer favored as the cilia do have movement, but are merely inefficient or unsynchronized.
A basal body is a protein structure found at the base of a eukaryotic undulipodium. 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.
An axoneme, also called an axial filament is the microtubule-based cytoskeletal structure that forms the core of a cilium or flagellum. Cilia and flagella are found on many cells, organisms, and microorganisms, to provide motility. The axoneme serves as the "skeleton" of these organelles, both giving support to the structure and, in some cases, the ability to bend. Though distinctions of function and length may be made between cilia and flagella, the internal structure of the axoneme is common to both.
Sperm is the male reproductive cell, or gamete, in anisogamous forms of sexual reproduction. Animals produce motile sperm with a tail known as a flagellum, which are known as spermatozoa, while some red algae and fungi produce non-motile sperm cells, known as spermatia. Flowering plants contain non-motile sperm inside pollen, while some more basal plants like ferns and some gymnosperms have motile sperm.
Intraflagellar transport or IFT is a bidirectional motility along axonemal microtubules that is essential for the formation (ciliogenesis) and maintenance of most eukaryotic cilia and flagella. It is thought to be required to build all cilia that assemble within a membrane projection from the cell surface. Plasmodium falciparum cilia and the sperm flagella of Drosophila are examples of cilia that assemble in the cytoplasm and do not require IFT. The process of IFT involves movement of large protein complexes called IFT particles or trains from the cell body to the ciliary tip and followed by their return to the cell body. The outward or anterograde movement is powered by kinesin-2 while the inward or retrograde movement is powered by cytoplasmic dynein 2/1b. The IFT particles are composed of about 20 proteins organized in two subcomplexes called complex A and B.
The radial spoke is a multi-unit protein structure found in the axonemes of eukaryotic cilia and flagella. Although experiments have determined the importance of the radial spoke in the proper function of these organelles, its structure and mode of action remain poorly understood.
An undulipodium or a 9+2 organelle is a motile filamentous intracellular projection of eukaryotic cells. It is basically synonymous to flagella and cilia which are differing terms for similar molecular structures used on different types of cells, and usually correspond to different waveforms.
Alstrom syndrome 1 also known as ALMS1 is a protein which in humans is encoded by the ALMS1 gene.
Sperm motility describes the ability of sperm to move properly through the female reproductive tract or through water to reach the egg. Sperm motility can also be thought of as the quality, which is a factor in successful conception; sperm that do not "swim" properly will not reach the egg in order to fertilize it. Sperm motility in mammals also facilitates the passage of the sperm through the cumulus oophorus and the zona pellucida, which surround the mammalian oocyte.
ADP/ATP translocase 4 (ANT4) is an enzyme that in humans is encoded by the SLC25A31 gene on chromosome 4. This enzyme inhibits apoptosis by catalyzing ADP/ATP exchange across the mitochondrial membranes and regulating membrane potential. In particular, ANT4 is essential to spermatogenesis, as it imports ATP into sperm mitochondria to support their development and survival. Outside this role, the SLC25AC31 gene has not been implicated in any human disease.
Voltage-dependent anion-selective channel protein 3 (VDAC3) is a protein that in humans is encoded by the VDAC3 gene on chromosome 8. The protein encoded by this gene is a voltage-dependent anion channel and shares high structural homology with the other VDAC isoforms. Nonetheless, VDAC3 demonstrates limited pore-forming ability and, instead, interacts with other proteins to perform its biological functions, including sperm flagella assembly and centriole assembly. Mutations in VDAC3 have been linked to male infertility, as well as Parkinson’s disease.
Ciliogenesis is defined as the building of the cell's antenna or extracellular fluid mediation mechanism. It includes the assembly and disassembly of the cilia during the cell cycle. Cilia are important organelles of cells and are involved in numerous activities such as cell signaling, processing developmental signals, and directing the flow of fluids such as mucus over and around cells. Due to the importance of these cell processes, defects in ciliogenesis can lead to numerous human diseases related to non-functioning cilia. Ciliogenesis may also play a role in the development of left/right handedness in humans.
The proximal centriole-like or PCL is an atypical type of centriole found in the sperm cells of insects. The PCL name is due to some similarity to the Proximal centriole found in Vertebrates sperm and the hypothesis that the two structures are homologous. The PCL is an atypical type of centriole because it does not have microtubules, a defining feature of centrioles. However, the PCL is a type of centriole for several reasons. (1) the PCL formation is dependent upon the same genetic pathway that mediates the initiation of centriole formation. (2) The PCL is composed of centriolar proteins. (3) After fertilization, the sperm PCL function like a centriole. The PCL recruits pericentriolar material (PCM) forming a centrosome that acts as a microtubule-organizing center (MTOC). The PCL also serves as a platform to form a typical centriole in the zygote, as expected from a centriole. Also, the PCL is essential to form one of the two spindle poles of the dividing zygote.
Compartmentalized ciliogenesis is the most common type of ciliogenesis where the cilium axoneme is formed separated from the cytoplasm by the ciliary membrane and a ciliary gate known as the transition zone.
References
- 1 2 3 Avidor-Reiss, Tomer; Leroux, Michel R. (December 2015). "Shared and Distinct Mechanisms of Compartmentalized and Cytosolic Ciliogenesis". Current Biology. 25 (23): R1143–R1150. doi:10.1016/j.cub.2015.11.001. PMC 5857621 . PMID 26654377.
- ↑ Avidor-Reiss, Tomer; Maer, Andreia M; Koundakjian, Edmund; Polyanovsky, Andrey; Keil, Thomas; Subramaniam, Shankar; Zuker, Charles S (May 2004). "Decoding Cilia Function". Cell. 117 (4): 527–539. doi: 10.1016/S0092-8674(04)00412-X . PMID 15137945.
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