Double-stranded DNA breaks hidden in the neutral Comet assay suggest a role of the sperm nuclear matrix in DNA integrity maintenance.

We used a mouse model in which sperm DNA damage was induced to understand the relationship of double-stranded DNA (dsDNA) breaks to sperm chromatin structure and to the Comet assay. Sperm chromatin fragmentation (SCF) produces dsDNA breaks located on the matrix attachment regions, between protamine toroids. In this model, epididymal sperm induced to undergo SCF can religate dsDNA breaks while vas deferens sperm cannot. Here, we demonstrated that the conventional neutral Comet assay underestimates the epididymal SCF breaks because the broken DNA ends remain attached to the nuclear matrix, causing the DNA to remain associated with the dispersion halo, and the Comet tails to be weak. Therefore, we term these hidden dsDNA breaks. When the Comet assay was modified to include an additional incubation with sodium dodecyl sulfate (SDS) and dithiothreitol (DTT) after the conventional lysis, thereby solubilizing the nuclear matrix, the broken DNA was released from the matrix, which resulted in a reduction of the sperm head halo and an increase in the Comet tail length, exposing the hidden dsDNA breaks. Conversely, SCF-induced vas deferens sperm had small halos and long tails with the conventional neutral Comet assay, suggesting that the broken DNA ends were not tethered to the nuclear matrix. These results suggest that the attachment to the nuclear matrix is crucial for the religation of SCF-induced DNA breaks in sperm. Our data suggest that the neutral Comet assay identifies only dsDNA breaks that are released from the nuclear matrix and that the addition of an SDS treatment can reveal these hidden dsDNA breaks.

Sperm DNA fragmentation: awakening the sleeping genome.

We have recently demonstrated that mammalian spermatozoa have the ability to degrade their DNA by a mechanism that is similar to apoptosis in somatic cells. When this mechanism is activated, the DNA is first degraded into loop-sized fragments by TOP2B (topoisomerase IIB). This degradation, termed sperm chromatin fragmentation, can be reversed by EDTA, which causes TOP2B to religate the double-stranded breaks it originally produced. Under certain conditions, a nuclease then degrades the sperm DNA further, digesting the entire sperm genome. When mouse spermatozoa which have been treated to induce TOP2B-mediated DNA breaks are injected into oocytes, the paternal DNA is specifically and completely degraded. This total digestion of paternal DNA occurs at the time of DNA synthesis initiation. In the present study, we explore the significance of an active TOP2B in the nucleus for mouse sperm function.

Changes in DNA loop domain structure during spermatogenesis and embryogenesis in the Syrian golden hamster.

The DNA in eukaryotic cells is organized into loop domains that are 25 to 100 kilobases long and attached at their bases to the nuclear matrix. This organization plays major roles in DNA replication and transcription. We examined changes in DNA loop structure of the 5S rDNA gene cluster in the Syrian golden hamster as a function of cellular differentiation by direct visualization with fluorescent in situ hybridization. The 5S rDNA cluster is large enough to encompass more than one loop domain but small enough that individual loop domains can still be resolved. We found that the sizes of the 5S rDNA loops are much smaller, and that the numbers of loops per locus are larger, in all pluripotent cell types than they are in adult somatic tissue. Within the pluripotent spermatogenic cell lineage, the loop domain organization was cell specific. The loop size decreased during the early stages of spermatogenesis but did not change during spermiogenesis, suggesting that DNA loop structure is independent of the chromatin condensation that occurs when protamines replace histones. In early embryonic cells, the loop structure remained small, but in differentiated somatic cells, it became much larger. We suggest that these changes in the 5S rDNA loop domain structure may be related to the maintenance or loss of developmental potential.

Further evidence that sperm nuclear proteins are necessary for embryogenesis.

We have recently presented evidence that the structural integrity of the mouse sperm nuclear matrix may be necessary for the proper unpackaging of sperm DNA for participation in embryogenesis. It is likely that the sperm nuclear matrix contributes to the organisation of the sperm DNA and its disturbance can seriously damage the paternal genome or its expression. In this work, we confirm our previous data and further suggest that even very subtle changes in the sperm nuclear structure may have a significant impact on embryo development. As reported previously, dithiothreitol (DTT) in the presence of an ionic detergent, ATAB, destabilized the nuclear matrix as measured by the halo assay, and oocytes injected with these nuclei failed to develop. We also discovered that omitting the protease inhibitor PMSF from the buffers used to extract spermatozoa prevented sperm injected into oocytes from participating in development. The organization of DNA into loop domains by the nuclear matrix in these nuclei appeared normal, as measured by the halo assay. Oocytes injected with sperm nuclei that had been washed with ATAB in the presence of phenylmethylsulphonyl fluoride (PMSF) but in the absence of DTT resulted in live births. Neither DTT treatment nor the absence of PMSF would be expected to disrupt the integrity of the paternal DNA. The data therefore suggest that even very subtle alterations in the structural proteins of the nucleus are enough to deprive sperm DNA of the ability to contribute to embryonic development.

Interaction of exogenous DNA with the nuclear matrix of live spermatozoa.

Sperm chromatin is a highly organized array of protamines and DNA, with the protamines serving to tightly condense the DNA into a compact, defined structure. We have previously demonstrated that the sperm nucleus is an ordered library of DNA organized into functional zones, such as the nuclear matrix and nuclear annulus. Other laboratories have suggested that mouse spermatozoa can interact with exogenous pSV2CAT plasmid DNA. In this work, we explored this interaction and examined the subcellular localization of the exogenous DNA. We found a repeatable association of exogenous DNA with a specific region of the sperm nuclear matrix. This region of the nucleus correlates with the equatorial segment of the sperm head. This interaction requires only a defined fertilization media, transfection quality DNA, and incubation with spermatozoa.

DNA organization in patients with a history of cryptorchidism.

OBJECTIVES: Cryptorchidism is associated with infertility, even in those patients with unilateral undescended testes. The mechanism for this infertility is not understood. We demonstrated recently that in mice, a stable nuclear matrix, a structural component of the nucleus that organizes DNA, is necessary for proper embryogenesis. We tested the hypothesis that spermatozoa from cryptorchid patients had unstable nuclear matrices. METHODS: Semen samples from 7 patients with a history of undescended testes and decreased fertility were tested for sperm nuclear matrix stability using our halo assay. RESULTS: All 7 patients were found to have unstable nuclear matrices, as compared with controls. CONCLUSIONS: This preliminary study suggests that one factor in the decreased fertility of cryptorchid patients may be unstable sperm nuclear matrices.

DNA loop domain organization: the three-dimensional genomic code.

It is well known that aberrations in the nuclear matrix contribute to the development of cancer, but many aspects of this process remain unknown. The mammalian sperm nuclear matrix serves as a distinctive model of DNA loop domain organization by the nuclear matrix since the integrity of the DNA structure can be measured by the ability of the paternal chromosomes to participate in embryogenesis. The structure of the nuclear matrix is known to be important for normal cellular functions such as transcriptional regulation and DNA replication. Even small aberrations in DNA structural organization in the sperm cell could have disastrous consequences for the embryo if they were essential for function. Recent work from our laboratory suggests that sperm nuclei with disrupted nuclear matrix structures but intact DNA cannot participate fully in embryogenesis, suggesting that the structural organization of DNA may provide important, heritable information that is necessary for development. We term the DNA sequence together with its three-dimensional organization the "genomic code." We suggest that the sperm nucleus is an ideal model for understanding the principles of the involvement of the three-dimensional structure of DNA in normal cellular function. Finally, the implications for cancer about what we can learn using sperm DNA as a model about the "genomic code" are discussed. J. Cell. Biochem. Suppl. 35:23-26, 2000.

Military free fall training injuries.

Military free fall or HALO (high altitude-low opening) is a distinct form of tactical parachuting used by the elite forces of the U.S. military. This study was undertaken to examine the type, location, and mechanism of injuries sustained by the military HALO parachutist during training. A retrospective study identified 134 parachutists with 141 injuries attributed to HALO training. The most common injuries were fractures (35.5%) and sprains/strains (34.7%). The sites most commonly injured were the lower extremities (52.5%), upper extremities (19.8%), and spine (14.9%). Landing was the most frequently encountered mechanism of injury (61.2%), followed by ground free fall simulation (wind tunnel training) and canopy deployment. Night jumping, wearing of combat equipment, and use of oxygen during high-altitude jumps were all variables that contributed to injury. The military free fall parachutist is predisposed to a wide array of musculoskeletal injuries at different training phases.

An intact sperm nuclear matrix may be necessary for the mouse paternal genome to participate in embryonic development.

We have been interested in determining the minimally required elements in the sperm head that are necessary in order for the paternal genome to participate in embryogenesis. We used an ionic detergent, mixed alkyltrimethylammonium bromide (ATAB), plus dithiothreitol (DTT) to remove the acrosome and almost all of the perinuclear theca, leaving only the sperm nucleus morphologically intact. We also tested the stability of the sperm nuclear matrix by the ability to form nuclear halos. Sperm nuclei washed in freshly prepared 0.5% ATAB + 2 mM DTT completely decondensed when extracted with salt, but nuclei washed in the same buffer that was 1 wk old, and then extracted with salt, produced nuclear halos, indicating stable nuclear matrices. When we treated sperm heads with freshly prepared ATAB+DTT and injected them into oocytes, none of the oocytes developed into live offspring. In contrast, sperm heads treated in the same way but with 1-wk-old ATAB+DTT solution could support development of about 30% of the oocytes to live offspring. Electron microscopy demonstrated that most of the perinuclear theca had been removed in both cases. These data suggest that at least in the mouse, the only component of the spermatozoa that is crucial for participation in embryologic development is the sperm nucleus with a stable nuclear matrix.

Can alcohol retain the reproductive and genetic potential of sperm nuclei? Chromosome analysis of mouse spermatozoa stored in alcohol.

Alcohol is known to preserve genomic DNA and the primary structure of sperm protamines. To determine whether alcohol can retain the genetic and reproductive potential of mammalian sperm nuclei, mature mouse spermatozoa were stored in 70% ethanol or propanol for up to 2 months before injection into oocytes. Live offspring were obtained after injection of spermatozoa stored in 70% ethanol for 1 day at -20 degrees C. About 20% of the spermatozoa stored under this condition had normal chromosomes. The remaining 80% of spermatozoa and all the spermatozoa stored in 70% ethanol for 2 months had structurally aberrant chromosomes, and none could support the development of normal embryos. High concentrations of alcohol do not alter the primary structure of either DNA or small-molecular-weight protamines. However, alcohol may modify protamine-protamine or protamine-DNA interactions in a manner that results in the induction of DNA strand breaks during sperm chromatin decondensation within the oocyte. The limited success in obtaining normal offspring with ethanol-stored spermatozoa is encouraging. It may be possible to overcome these problems and develop a simple method for preserving mammalian spermatozoa without freezing.

National trends in the epidemiology of prostate cancer, 1973 to 1994: evidence for the effectiveness of prostate-specific antigen screening.

OBJECTIVES: The use of prostate-specific antigen (PSA) to screen for prostate cancer remains controversial. Although it is still too early to measure directly the effects of PSA screening on mortality, we examined changes in the epidemiology of prostate cancer to determine if there is other evidence of the effectiveness of PSA as a screening tool. METHODS: We examined trends in age at diagnosis, and age-adjusted trends in stage and grade at diagnosis, for 140,936 white and 15,662 African American men diagnosed with prostate cancer from 1973 to 1994 in the National Cancer Institute's Surveillance Epidemiology and End Results data base. RESULTS: We found a significant downward trend in age at diagnosis, concomitant with a downward shift in stage of disease at diagnosis, starting with the advent of the PSA era in the late 1980s. We noted most cancers detected since the PSA era to be moderately well differentiated (International Classification of Diseases of the World Health Organization grade 2; Gleason score 5, 6, 7) and organ confined. Although findings were similar for both whites and African Americans, African Americans experienced a greater increase in poorly differentiated disease than did whites. CONCLUSIONS: Changes in the epidemiology of prostate cancer since the advent of the PSA era are consistent with the introduction of an effective screening test. This is evidenced by an increase in detection of significant prostate cancer in individuals who will likely benefit from treatment.

Correlation of mechanical imaging and histopathology of radical prostatectomy specimens: a pilot study for detecting prostate cancer.

PURPOSE: A new modality termed mechanical imaging has recently been developed. We determined whether mechanical imaging could be used to detect prostate cancer in radical prostatectomy specimens. MATERIALS AND METHODS: Stress patterns on the surface of excised prostates were evaluated using the data obtained from a planar piezoelectric resistive force sensor array. Seven radical prostatectomy and 2 cystoprostatectomy specimens were manually palpated and evaluated by the mechanical imager. The prostates were histopathologically analyzed for the presence of cancer. The results of the manual palpation, mechanical imaging and pathological analysis were correlated. RESULTS: Mechanical imaging correlated closely with nodules palpated in all specimens and in 1 it revealed a suspicious area undetected by palpation, which on subsequent histological analysis demonstrated carcinoma. CONCLUSIONS: Mechanical imaging can detect areas of heterogeneity in prostate tissue which correlate with cancer. Our findings provide the basis for the development of a transrectal mechanical imaging probe for prostate cancer detection.

Trends in poorly differentiated prostate cancer 1973 to 1994: observations from the Surveillance, Epidemiology and End Results database.

PURPOSE: Using the Surveillance, Epidemiology and End Results Program, we evaluated the changing demographics of poorly differentiated prostate cancer since early detection measures, such as serum prostate specific antigen screening, were introduced into clinical practice in the United States. MATERIALS AND METHODS: Trends between 1973 and 1994 in the proportion, stage and treatment of poorly differentiated tumors (International Classification of Diseases [ICD]-O code 3, Gleason score 8, 9, 10) were assessed, and multivariate Cox proportional hazards models were used to identify independent correlates of disease specific survival. RESULTS: The number of ICD-O grade 3 tumors increased during the study period, although these comprised a decreased proportion of all diagnosed cases (24.4% of 29,588 in 1980 to 1984 versus 21.4% of 81,932 in 1990 to 1994, chi-square p < 0.001). ICD-O grade 3 tumors were less often metastatic in 1990 to 1994 compared to 1980 to 1984 (17.4% versus 33.1%, chi-square p < 0.0001) and more often treated with radical prostatectomy or radiotherapy in 1990 to 1994 compared to 1983 to 1984 (37.5 versus 15.6%, chi-square p < 0.001). Although treatment group (radiotherapy versus radical prostatectomy) among patients with clinically confined tumors was an independent correlate of disease specific survival (hazard ratio 2.3, 1983 to 1984 and 3.3, 1990 to 1994), one must recognize potential selection biases inherent to this nonrandomized tumor registry study. The observed 12-year actuarial disease specific survival rates were 67.6% for radical prostatectomy and 46.3% for radiotherapy. CONCLUSIONS: In the present era ICD-O grade 3 tumors are being detected in increasing number, are less likely to be metastatic at presentation and are more likely to be treated definitively with radical prostatectomy or radiotherapy. Disease specific survival rates observed with radical prostatectomy and radiotherapy in patients with clinically confined tumors support current efforts to detect and treat these highly aggressive tumors while clinically localized.

Localization of three genes in the hook-shaped hamster sperm nucleus by fluorescent in situ hybridization.

We mapped the positions of three different genes in the flat, hook-shaped hamster sperm nucleus to determine the specificity of sperm DNA positioning. The positions of the 5S rRNA gene cluster, the CAD gene, and the class I 1.6 gene were determined by fluorescent in situ hybridization (FISH) in over 50 hamster sperm nuclei for each gene. We first demonstrated by FISH with mitotic chromosomes that the latter two genes were localized on the same chromosome. Within the sperm nuclei, we found that the precise position was variable for each of the three genes, but that there were two areas of preferred localization that contained 26-31% of the nuclear area and within which 80% of the signals were located. Nuclei were then hybridized to two genes simultaneously, using either two genes located on the same chromosome or two genes located on different chromosomes. We found no preference for orientation of one gene relative to the other for either pair of genes examined. This suggested that the relative arrangements of chromosomes within the sperm nucleus are flexible. These data demonstrate that the topographical arrangements of genes within the hamster sperm nucleus have a limited plasticity allowing for a relatively large range of possible localization.

The unique, complex organization of the transcriptionally silent sperm chromatin.

The sperm nucleus contains one haploid copy of the genome that is completely transcriptionally silent and is not being replicated. Recent evidence has revealed that this "silent" chromatin nevertheless contains a complex organization at all levels. This includes DNA loop domain formation by the sperm nuclear matrix that is gene specific and highly ordered folding patterns of the chromosomes, particularly with respect to centromere and telomere positioning. Such specificity in the sperm DNA organization suggests functional requirements for their existence. As these begin to emerge, the sperm nucleus is becoming an important model for the study of the eukaryotic genome.

Cell-specific organization of the 5S ribosomal RNA gene cluster DNA loop domains in spermatozoa and somatic cells.

DNA in eucaryotic cells is organized into loop domains, ranging in size from 25 to 100 kb, that are attached at their bases to the structural component of the nucleus termed the nuclear matrix. These DNA loop domains have been shown to be important in the regulation of both DNA replication and RNA transcription. In this study we have compared the structural organization of the DNA loop domains of the 5S rRNA gene cluster in sperm, liver, and brain nuclei in the Syrian golden hamster. The individual loop domains were visualized by fluorescent in situ hybridization to protamine (sperm)- and histone (somatic)-depleted nuclei, termed nuclear matrix halo preparations. We found that in sperm nuclei, the 5S rRNA gene cluster was organized into three small loop domains that were approximately 48 kb each. In both types of somatic cell nuclei examined, the 5S rRNA gene cluster was organized into a single, much larger loop domain that was up to 480 kb in length. The data suggest that at least some of the compaction that sperm DNA undergoes during spermiogenesis is mediated by the nuclear matrix independent of protamine binding. Additionally, this sperm-specific DNA organization may be involved in the specific patterns of DNA replication and transcription of the paternal genome in the embryo.

Structure of the rRNA genes in the hamster sperm nucleus.

We have examined the structure of the major ribosomal RNA (rRNA) genes in the hamster sperm nucleus, using fluorescent in situ hybridization (FISH). The rRNA genes are present as tandemly repeated clusters located at the telomeric ends of the short arms of five pairs of acrocentric chromosomes in the Syrian golden hamster (as they are in humans). In somatic cells, these five chromosome pairs come together to form the nucleolus, the site of rRNA synthesis. The nucleolus remains intact through S phase of the cell cycle, breaking apart only during late G2 and mitosis when the chromosomes condense. Mammalian sperm nuclei are the final products of meiotic division and morphological differentiation that includes a dramatic chromatin condensation. Consequently, it was not immediately obvious whether the rRNA genes would be condensed into a nucleolus-like structure in the mature spermatozoa, or separated, as they are in mitotic chromosomes. We found that of 117 sperm nuclei examined, 91.5% contained between two and five FISH signals for the rRNA gene clusters, and 64.0% contained four (29%) or five (35%) signals. In decondensed hamster sperm nuclei, the rRNA hybridized signals were separated into independent strands. These data collectively indicate that the chromosomes containing the rRNA genes are not bound together into a pre-nucleolar structure in fully condensed mammalian sperm nuclei.

Elastin morphology in normal and obstructed guinea-pig bladders. Localization of elastin to the trigone.

Elastin is the major component of elastic fibers in aortic tissue and has been suggested to be important for the stretch and recoil of the bladder. We have mapped the histologic distribution of elastin throughout the entire guinea-pig bladder as well as changes in the distribution of elastin during bladder-outlet obstruction. We used an animal model in which a jeweler's ring is placed around the urethra of the young guinea pig. As the animal grows, outlet obstruction is gradually induced, and the bladder gradually increases in total weight to as much as 8-fold that of controls. We localized the elastin histologically in normal and obstructed bladders by serially sectioning entire bladders and staining the sections with an elastin-specific stain, Verhoff-van Gieson stain (VVG). Surprisingly, we found that the elastin was predominantly localized only to the trigone of the bladder and that the elastin in this area was increased during obstruction. These results are consistent with the predominantly mesodermal embryologic origin of the trigone, since mesodermal tissues are more often associated with elastin expression.

The structure of the sleeping genome: implications of sperm DNA organization for somatic cells.

The tertiary structure of the DNA that makes up the eukaryotic genome is remarkably plastic, taking many different forms in response to the different needs of the cell. During the cell cycle of one cell, the DNA is replicated, reorganized into mitotic chromosomes, and decondensed into interphase chromatin. Within one cell at any given point in time, the chromatin is divided into hetero- and euchromatin reflecting active and inactive states of the DNA. This organization varies within one organism since different parts of the genome are active in different cell types. This article focuses on the most dramatic cell-type-specific DNA organization, that found in spermatozoa, in which the entire genome is reorganized into an inactive state that is more highly condensed than mitotic chromosomes. This unique example of eukaryotic DNA organization offers some interesting clues to the still unanswered questions about the role that the three-dimensional packaging of DNA plays in its function.