[Analysis of sperm chromosomes in infertile males with teratozoospermia]. / Analiza chromosomów plemników od pacjentów z teratozoospermia.

OBJECTIVES: The aim of the study was to examine sperm chromosomes from infertile males with teratozoospermia. DESIGN: Basic research study MATERIALS AND METHODS: Spermatozoa were obtained from infertile males with teratozoospermia. Intracytoplasmic sperm injection was used to inject human spermatozoa into mouse oocytes in order to examine sperm chromosomes. RESULTS: Chromosomes of spermatozoa obtained from 6 infertile teratozoospermic and 1 fertile normozoospermic males were investigated. The mean frequency of structural chromosome aberrations in amorphous, motile spermatozoa was similar to that of morphologically normal sperm (9 vs. 7.7%). The structural aberrations found in amorphous, immotile spermatozoa reached 93% and revealed severity was significant. CONCLUSIONS: Teratozoospermia per se did not increase the frequency of structural chromosome aberrations in sperm. Severe chromosomal damage was revealed when immotile spermatozoa were injected into oocytes by ICSI.

Expression of foreign DNA is associated with paternal chromosome degradation in intracytoplasmic sperm injection-mediated transgenesis in the mouse.

The efficiency of intracytoplasmic sperm injection (ICSI)-mediated transgenesis is often limited by poor embryo development. Because our previous work indicated that impairment of embryo development is frequently related to chromosomal abnormalities, we hypothesized that foreign DNA and/or conditions used to enhance integration of the DNA might induce chromosome damage. Therefore, we examined the chromosomes of mouse embryos produced by transgenesis with the EGFP gene. Spermatozoa were processed with three methods that cause membrane disruption: freeze-thawing, Triton X-100, or Triton X-100 followed by a sucrose wash. Membrane-disrupted spermatozoa were mixed with EGFP plasmids and injected into metaphase II oocytes. Three endpoints were evaluated: paternal chromosomes of the zygote, embryo capacity to develop in vitro, and expression of the transgene at the morula/blastocyst stage. In all pretreatments, we observed a significant decrease (approximately 2-fold) in the frequency of normal karyoplates when spermatozoa were incubated with exogenous DNA as compared with the treatment when no DNA was added. As predicted, embryo development was correlated with the integrity of the paternal chromosomes of the zygote. Searching for the possible mechanism of chromosome degradation, we used the ion chelators EGTA and EDTA and found that they neutralize the harmful effect of the transgene and stabilize the paternal chromosomes. In the presence of chelating agents, however, the number of embryos expressing EGFP produced with ICSI-mediated transgenesis decreased significantly. The results suggest that treatment of spermatozoa with exogenous DNA leads to paternal chromosome degradation in the zygote. Furthermore, the mechanisms of disruption of paternal chromosomes and the integration of foreign DNA may be closely related.

Combination of dithiothreitol and detergent treatment of spermatozoa causes paternal chromosomal damage.

Treatment of spermatozoa with either the nonionic detergent Triton X-100 (TX) or dithiothreitol (DTT) has been suggested to confer enhanced success on intracytoplasmic sperm injection (ICSI) in mice and humans. Here, we attempted to use both reagents together, to our knowledge for the first time, and found that this caused severe chromosomal breaks in paternal pronuclei. We documented this effect further by treating mouse spermatozoa with several combinations of DTT with and without detergent. Spermatozoa were treated with vigorous pipetting to induce membrane disruption or with TX or the ionic detergent mixed alkyltrimethylammonium bromide (ATAB). Swim-up spermatozoa were used as controls. In each treatment, two samples were tested, with or without the addition of DTT during the treatment procedure. In all samples with DTT, protamine reduction was confirmed by the decondensation assay. Sperm nuclei obtained after different treatments were injected into oocytes for cytogenetic analysis, and paternal and maternal chromosomes of the zygote were visualized and examined. We found that the numbers of normal paternal karyoplates resulting from ICSI with spermatozoa treated with either DTT (87%, 153/176), TX (79%, 112/142), or ATAB (85%, 99/116) alone were similar to swim-up controls (92%, 103/112). However, only 22% (23/103) and 40% (59/149) of examined metaphases were scored as normal in TX + DTT or ATAB + DTT treatments, respectively. Spermatozoa in which the membranes were disrupted by vigorous pipetting in the presence of DTT had a slightly reduced frequency of normal chromosomes (61%, 64/104), whereas those without DTT were normal (79%, 125/159). However, this difference was not statistically significant. When spermatozoa were treated with TX + DTT in the presence of EGTA or a mixture of EGTA and EDTA, the frequency of normal chromosomes was 39% (45/114) and 47% (38/81), respectively, suggesting that endogenous sperm nucleases may play a role in chromosomal damage. Our results indicate that simultaneous treatment of spermatozoa with detergent and DTT induces extensive chromosomal breakage and, therefore, should not be attempted in ICSI.

Intracytoplasmic sperm injection is more efficient than in vitro fertilization for generating mouse embryos from cryopreserved spermatozoa.

Efficient and dependable mouse cryopreservation methods are urgently needed because the production of mice with transgenes and disrupted and mutant genes is now commonplace. Preservation of these unique genomes provides an essential safeguard for future research. Unfortunately, mouse spermatozoa appear more vulnerable to freezing than other species, e.g., bovine and human. In this study, we examined the efficiency of intracytoplasmic sperm injection (ICSI) and in vitro fertilization (IVF) in generating embryos from mouse spermatozoa frozen with 18% raffinose and 3% skim milk for cryoprotection. A comparison was made between the inbred strain C57BL/6J, commonly used in mutagenic and transgenic studies, and a hybrid strain B6D2F1 (C57BL/6J x DBA/2J). C57BL/6J spermatozoa are known to be more sensitive to freezing than B6D2F1. Fertilization of oocytes after IVF was significantly lower with C57BL/6J spermatozoa when compared with B6D2F1 spermatozoa for both fresh and frozen spermatozoa (fresh, 89 vs. 55%; frozen, 56 vs. 9%). Freezing also reduced the fertility of B6D2F1 spermatozoa (89 vs. 56%). Fertilization improved dramatically after ICSI with fresh and frozen C57BL/6J spermatozoa (90 and 85%) and also with frozen B6D2F1 spermatozoa (87%). The development of two-cell embryos to the blastocyst stage was lower for C57BL/6J than B6D2F1 (42-61% and 84-98%) in all treatments but similar for embryos within each strain. The normality of chromosomes from fresh and frozen spermatozoa was assessed in oocytes prior to first cleavage. The majority of oocytes had normal chromosomes after IVF (98-100%) and ICSI (87-95%), indicating that chromosomal abnormalities were not responsible for the poorer development in vitro of C57BL/6J embryos. In conclusion, our data show that ICSI is a more efficient and effective technique than IVF for generating embryos from frozen spermatozoa. More important, ICSI is especially valuable for strains where IVF with fresh spermatozoa produces few or no embryos.

Sperm nuclear halos can transform into normal chromosomes after injection into oocytes.

Mouse sperm nuclei extracted with an ionic detergent and 2 M NaCl retain their overall morphology, but upon subsequent reduction of the protamine disulfides they lose all elements of chromatin structure except the organization of DNA into loop that are anchored to the nuclear matrix. These DNA loops appear as a halo surrounding the nuclear matrix, and nuclei extracted in this manner are, therefore, called nuclear halos. Here, we report that sperm nuclear halos injected into oocytes can form pronuclei, then transform into chromosomes with normal morphology. This suggests that sperm nuclear halos retain all the information necessary for normal chromosomal organization, and that micromanipulation of these extracted sperm nuclei can be accomplished without major DNA damage.

Separation of motile populations of spermatozoa prior to freezing is beneficial for subsequent fertilization in vitro: a study with various mouse strains.

Success with in vitro fertilization (IVF) using inbred strains of mice varies considerably and appears to be related to the proportion of motile spermatozoa present in epididymal sperm samples of different strains. In this study, motile spermatozoa were separated from the original samples using a column of Sephadex G25. IVF rates were compared between separated and nonseparated samples of epididymal spermatozoa before and after cryopreservation. Oocytes and spermatozoa were obtained from FVB, DBA/2, C57BL/6J, and BALB/c inbred mice; and from F1 (C57BL/6J;ts DBA/2) hybrid mice, and isogenic gametes were used for IVF. These strains of mice were chosen because of their common use in transgenesis and mutagenesis studies. Dulbecco PBS was used for sperm separation on Sephadex, 18% raffinose, and 3% skim milk for cryopreservation; T6 medium for IVF; and mKSOM(AA) for embryo culture. There was a marked improvement in the rate of fertilization using fresh spermatozoa after motile spermatozoa were separated in C57BL/6J and BALB/c strains (92% vs. 58%, 79% vs. 44%) but no differences were found in fertilization rates between separated and nonseparated spermatozoa in F1, FVB, and DBA/2 strains (99% vs. 83%, 95% vs. 93%, 86% vs. 87%, respectively). After cryopreservation, higher rates of fertilization were obtained with separated motile samples in all strains; the greatest improvements were obtained with spermatozoa from C57BL/6J and BALB/c strains (40% vs. 16% and 51% vs. 14% for separated and nonseparated spermatozoa, respectively). No differences were found between the proportions of 14.5-day fetuses developing from embryos derived from separated and nonseparated spermatozoa with or without cryopreservation (33% to 46%). In conclusion, the fertility of frozen-thawed mouse epididymal spermatozoa improves significantly when highly motile populations of spermatozoa are separated for freezing.