Preferable location of chromosomes 1, 29, and X in bovine spermatozoa.

Chromosome positioning in sperm nucleus may have a functional significance by influencing the sequence of post-fertilization events. In this study we present data on preferential locations of chromosomes 1, 29 and X in spermatozoa. Here we demonstrate that the position of X chromosome in the sperm nucleus is more restricted as compared to the position of chromosome 1, which is about of the same size.

Positioning of chromosomes in human spermatozoa is determined by ordered centromere arrangement.

The intranuclear positioning of chromosomes (CHRs) is a well-documented fact; however, mechanisms directing such ordering remain unclear. Unlike somatic cells, human spermatozoa contain distinct spatial markers and have asymmetric nuclei which make them a unique model for localizing CHR territories and matching peri-centromere domains. In this study, we established statistically preferential longitudinal and lateral positioning for eight CHRs.

Protamine withdrawal from human sperm nuclei following heterologous ICSI into hamster oocytes.

During late stages of spermatogenesis in mammals, most histones bound to DNA are replaced by protamines (PRM), which results in formation of supercondensed and genetically inert sperm chromatin. At fertilization, mature spermatozoon penetrates oocyte and chromatin is remodeled "back" from nucleoprotamine to nucleohistone state. While being crucial for activation of male genome and ultimately for initiation of embryonic development, this process is poorly studied, especially in humans.

Kinetics of human male pronuclear development in a heterologous ICSI model.

Purpose: To evaluate human sperm nuclear chromatin decondensation in a heterologous ICSI system using hamster ova injected with human sperm.

Materials And Methods: Frozen hamster oocytes were injected with Triton X-100 treated sperm and fixed at different time points post ICSI. Oocytes injected with non-treated sperm served as controls.

Reorganisation of human sperm nuclear architecture during formation of pronuclei in a model system.

By fertilisation, two terminally differentiated cells, namely the egg and spermatozoon, are combined to create a totipotent zygote. During this process, the inactive sperm nucleus is transformed into a functional male pronucleus. Recent studies demonstrate that human sperm chromatin has an elaborate multilevel organisation, but almost nothing is known about how sperm chromosomes are transformed during fertilisation.

Sperm chromatin released by nucleases.

In human spermatozoa, 15-20% of histones are retained in the nucleus to coexist with protamines. Hypothetically, nucleohistone regions of sperm chromatin mark DNA sequences for distinctive processing during fertilization and early embryogenesis. The structural organization and molecular composition of nucleohistones in human spermatozoa is poorly studied.

Organization of chromosomes in spermatozoa: an additional layer of epigenetic information?

Elaborate non-random organization of human sperm chromosomes at different structural levels, starting from the DNA packing by protamines up to the higher-order chromosome configuration and nuclear positioning of chromosome territories, has been discovered. Here, we put forward a hypothesis that the unique genome architecture in sperm provides a mechanism for orchestrated unpacking and ordered activation of the male genome during fertilization, thus offering an additional level of epigenetic information that will be deciphered in the descendant cells.

Characterisation of a human sperm cell subpopulation marked by the presence of the TSH2B histone.

During the process of mammalian spermiogenesis, a significant reorganisation of the chromatin structure occurs involving the sequential substitution of somatic histones with protamines. In the human sperm nucleus, approximately 15% of the basic nuclear protein complement is maintained as histones. Human testis/sperm-specific histone H2B (hTSH2B) is a variant of the histone H2B expressed exclusively in spermatogenic germline cells and present in some mature sperm cells.

Testis/sperm-specific histone 2B in the sperm of donors and subfertile patients: variability and relation to chromatin packaging.

Background: The compaction of human sperm chromatin is the result of replacement of approximately 85% of histones with protamines. Germ-line testis/sperm-specific histone 2B (TSH2B) has been detected in only approximately 30% of mature spermatozoa. Its level in the semen of subfertile patients varies; its function is unknown.

Chromosome architecture in the decondensing human sperm nucleus.

Whereas recent studies demonstrated a well-defined nuclear architecture in human sperm nuclei, little is known about the mode of DNA compaction above the elementary structural unit of nucleoprotamine toroids. Here, using fluorescence in-situ hybridization (FISH) with arm-specific DNA probes of chromosomes 1, 2 and 5, we visualized arm domains and established hierarchical levels of sperm chromatin structures. The compact chromosome territories, which in sperm have a preferred intranuclear localization, have an extended conformation represented by a 2000 nm chromatin fiber.

Nature of telomere dimers and chromosome looping in human spermatozoa.

Specific and well-organized chromosome architecture in human sperm cells is supported by the prominent interactions between centromeres and between telomeres. The telomere-telomere interactions result in telomere dimers that are positioned at the nuclear periphery. It is unknown whether composition of sperm telomere dimers is random or specific.

Novel human testis-specific histone H2B encoded by the interrupted gene on the X chromosome.

Testis-specific histones are synthesized and accumulated at specific stages of mammalian spermatogenesis. Their proposed functions range from facilitation of the replacement of somatic histones by protamines to epigenetic control of gene transcription. Several testis histone variants were characterized in mouse and rat; however, few are known in humans.

Male germline-specific histones in mouse and man.

In mice and humans, the production of male gametes is a result of a complex multistep process of stem cell differentiation. The final product, the mature spermatozoon, is designed for the safe delivery of a haploid copy of the paternal genetic information to the oocyte in a structural state suitable for zygote formation and embryogenesis. A remarkable structural reorganization of chromosomes in germline cells during mammalian spermatogenesis has been characterized.

Non-random positioning of chromosomes in human sperm nuclei.

In human spermatozoa, the arrangement of chromosomes is non-random. Characteristic features are association of centromeres in the interior chromocenter and peripheral location of telomeres. In this paper, we have investigated the highest level of order in DNA packing in sperm--absolute and relative intranuclear chromosome positioning.

[Recognition of internal (TTAGGG)n repeats by telomeric protein TRF1 and its role in maintenance of chromosomal stability in Chinese hamster cells].

Mammalian telomeres contain long tandem (TTAGGG)n repeats, which are protected by a complex of different proteins. Telomeric repeat-binding factors TRF1 and TRF2 play the key role in protection of telomeres through the formation of terminal loops (called T-loop). A T-loop isolates the 3' strand telomeric end and with this mechanism protects telomeres from the influence of enzymes of DNA reparation and telomere fusions and also interferes with the interaction of telomerase with telomeres.

Protection of internal (TTAGGG)n repeats in Chinese hamster cells by telomeric protein TRF1.

Chinese hamster cells have large interstitial (TTAGGG) bands (ITs) which are unstable and should be protected by an unknown mechanism. Here, we expressed in Chinese hamster V79 cells green fluorescent protein (GFP)-tagged human TRF1, and found that a major fraction of GFP-TRF1 bound to ITs is diffusionally mobile. This fraction strongly decreases after treatment of cells with wortmannin, a protein kinase inhibitor, and this drug also increases the frequency of chromosome aberrations.

Human testis/sperm-specific histone H2B (hTSH2B). Molecular cloning and characterization.

Human sperm, unlike the sperm of other mammals, contain replacement histones with unknown biological functions. Here, we report the identification of the novel human gene coding for a testis/sperm-specific histone H2B (hTSH2B). This variant histone is 85% homologous to somatic H2B and has over 93% homology with the testis H2B of rodents.

Telomeres in mammalian male germline cells.

Telomeres are terminal chromosomal domains that protect chromosome ends from degradation and fusion and promote complete replication of DNA. Telomeres are involved in the regulation of cellular replicative lifespan and tumorigenesis. These important functions of the telomeres have evoked high interest: numerous studies have resulted in a detailed description of telomere composition and structure in somatic cells.

A negative regulator of telomere-length protein trf1 is associated with interstitial (TTAGGG)n blocks in immortal Chinese hamster ovary cells.

Telomeres of mammalian chromosomes are composed of long tandem repeats (TTAGGG)n which bind in a sequence-specific manner two proteins-TRF1 and TRF2. In human somatic cells both proteins are mostly associated with telomeres and TRF1 overexpression resulting in telomere shortening. However, chromosomes of some mammalian species, e.

Human sperm telomere-binding complex involves histone H2B and secures telomere membrane attachment.

Telomeres are unique chromatin domains located at the ends of eukaryotic chromosomes. Telomere functions in somatic cells involve complexes between telomere proteins and TTAGGG DNA repeats. During the differentiation of germ-line cells, telomeres undergo significant reorganization most likely required for additional specific functions in meiosis and fertilization.

Chromatin structure of telomere domain in human sperm.

Telomeres in human sperm nucleus are clustered at the nuclear periphery. Chromosomes in the sperm are highly condensed with protamines, however, a small portion of DNA remains associated with histones; the role of the nucleohistone is unknown. To examine structure of the telomeric chromatin, the sperm nuclei were treated with micrococcal nuclease.

Identification and characterization of a bovine sperm protein that binds specifically to single-stranded telomeric deoxyribonucleic acid.

Telomere DNA at the physical termini of chromosomes forms a single-stranded 3' overhang. In lower eukaryotes, e.g.

Increased telomere size in sperm cells of mammals with long terminal (TTAGGG)n arrays.

An increase in the length of telomeres in human sperm compared to somatic cells has long been noted and considered within a popular hypothesis involving telomere shortening and cell aging. In the present study we determined telomere length in two species with long terminal TTAGGG arrays--bovine and porcine. Using several independent methods we demonstrate that the telomeres in the sperm of human, porcine and bovine are elongated by 69%, 24%, and 14%, respectively, in comparison with somatic tissues.

Telomere-telomere interactions and candidate telomere binding protein(s) in mammalian sperm cells.

We have used fluorescent in situ hybridization to localize telomeres within the nuclei of sperm from six mammals (human, rat, mouse, stallion, boar, and bull). In minimally swollen sperm of mouse and rat, most of the telomeres are clustered within a limited area in the posterior part of nuclei. In sperm of other species, telomeres associate into tetrameres and dimers.