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Chromatin is a complex of DNA, protein and RNA found in eukaryotic cells. Its primary function is packaging long DNA molecules into more compact, denser structures. This prevents the strands from becoming tangled and also plays important roles in reinforcing the DNA during cell division, preventing DNA damage, and regulating gene expression and DNA replication. During mitosis and meiosis, chromatin facilitates proper segregation of the chromosomes in anaphase; the characteristic shapes of chromosomes visible during this stage are the result of DNA being coiled into highly condensed chromatin.
In biology, histones are highly basic proteins abundant in lysine and arginine residues that are found in eukaryotic cell nuclei. They act as spools around which DNA winds to create structural units called nucleosomes. Nucleosomes in turn are wrapped into 30-nanometer fibers that form tightly packed chromatin. Histones prevent DNA from becoming tangled and protect it from DNA damage. In addition, histones play important roles in gene regulation and DNA replication. Without histones, unwound DNA in chromosomes would be very long. For example, each human cell has about 1.8 meters of DNA if completely stretched out, however when wound about histones, this length is reduced to about 90 micrometers (0.09 mm) of 30 nm diameter chromatin fibers.
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.
The spermatid is the haploid male gametid that results from division of secondary spermatocytes. As a result of meiosis, each spermatid contains only half of the genetic material present in the original primary spermatocyte.
Protamines are small, arginine-rich, nuclear proteins that replace histones late in the haploid phase of spermatogenesis and are believed essential for sperm head condensation and DNA stabilization. They may allow for denser packaging of DNA in the spermatozoon than histones, but they must be decompressed before the genetic data can be used for protein synthesis. However, in humans and maybe other primates, 10-15% of the sperm's genome is packaged by histones thought to bind genes that are essential for early embryonic development.
Spermiogenesis is the final stage of spermatogenesis, which sees the maturation of spermatids into mature spermatozoa. The spermatid is a more or less circular cell containing a nucleus, Golgi apparatus, centriole and mitochondria. All these components take part in forming the spermatozoon.
Nucleoproteins are any proteins that are structurally associated with nucleic acids, either DNA or RNA. Typical nucleoproteins include ribosomes, nucleosomes and viral nucleocapsid proteins.
Differential extraction refers to the process by which the DNA from two different types of cells can be extracted without mixing their contents. The most common application of this method is the extraction of DNA from vaginal epithelial cells and sperm cells from sexual assault cases in order to determine the DNA profiles of the victim and the perpetrator. Its success is based on the fact that sperm cells pack their DNA using protamines which are held together by disulfide bonds. The protamines sequester DNA from spermatozoa, making it more resilient to DNA extraction than DNA from epithelial cells.
In molecular biology and genetics, transcription coregulators are proteins that interact with transcription factors to either activate or repress the transcription of specific genes. Transcription coregulators that activate gene transcription are referred to as coactivators while those that repress are known as corepressors. The mechanism of action of transcription coregulators is to modify chromatin structure and thereby make the associated DNA more or less accessible to transcription. In humans several dozen to several hundred coregulators are known, depending on the level of confidence with which the characterisation of a protein as a coregulator can be made. One class of transcription coregulators modifies chromatin structure through covalent modification of histones. A second ATP dependent class modifies the conformation of chromatin.
Nuclear autoantigenic sperm protein is a protein that in humans is encoded by the NASP gene. Multiple isoforms are encoded by transcript variants of this gene.
Spermatid nuclear transition protein 1 is a protein that in humans is encoded by the TNP1 gene.
Nuclear transition protein 2 is a protein that in humans is encoded by the TNP2 gene.
H1 histone family, member N, testis-specific is a member of the histone family of nuclear proteins which are a component of chromatin. In humans, this protein is encoded by the H1FNT gene.
Histone H1oo is a protein that in humans is encoded by the H1FOO gene.
DNA condensation refers to the process of compacting DNA molecules in vitro or in vivo. Mechanistic details of DNA packing are essential for its functioning in the process of gene regulation in living systems. Condensed DNA often has surprising properties, which one would not predict from classical concepts of dilute solutions. Therefore, DNA condensation in vitro serves as a model system for many processes of physics, biochemistry and biology. In addition, DNA condensation has many potential applications in medicine and biotechnology.
Oocyteactivation is a series of processes that occur in the oocyte during fertilization.
Nucleoplasmin, the first identified molecular chaperone is a thermostable acidic protein with a pentameric structure. The protein was first isolated from Xenopus species
Histone variants are proteins that substitute for the core canonical histones in nucleosomes in eukaryotes and often confer specific structural and functional features. The term might also include a set of linker histone (H1) variants, which lack a distinct canonical isoform. The differences between the core canonical histones and their variants can be summarized as follows: (1) canonical histones are replication-dependent and are expressed during the S-phase of cell cycle whereas histone variants are replication-independent and are expressed during the whole cell cycle; (2) in animals, the genes encoding canonical histones are typically clustered along the chromosome, are present in multiple copies and are among the most conserved proteins known, whereas histone variants are often single-copy genes and show high degree of variation among species; (3) canonical histone genes lack introns and use a stem loop structure at the 3’ end of their mRNA, whereas histone variant genes may have introns and their mRNA tail is usually polyadenylated. Complex multicellular organisms typically have a large number of histone variants providing a variety of different functions. Recent data are accumulating about the roles of diverse histone variants highlighting the functional links between variants and the delicate regulation of organism development.
Protamine 1 is a protein that in humans is encoded by the PRM1 gene.
Protamine 2 is a protein that in humans is encoded by the PRM2 gene.
References
- Meistrich ML, Mohapatra B, Shirley CR, Zhao M. 2003. Role of transition nuclear proteins in spermiogenesis. Chromosoma 111:483-488.