Increased numbers of DNA-damaged spermatozoa in samples presenting an elevated rate of numerical chromosome abnormalities

STUDY QUESTION

Is there a relationship between DNA damage and numerical chromosome abnormalities in the sperm of infertile patients?

SUMMARY ANSWER

A strong link between DNA fragmentation and the presence of numerical chromosome abnormalities was detected in human sperm. Chromosomally abnormal spermatozoa were more likely to be affected by DNA fragmentation than those that were chromosomally normal.

WHAT IS KNOWN ALREADY

Several studies have described the presence of elevated levels of DNA damage or chromosome defects in the sperm of infertile or subfertile men. However, the nature of the relationship between sperm DNA damage and chromosome abnormalities is poorly understood. The fact that some assisted reproductive techniques have the potential to allow abnormal spermatozoa to achieve oocyte fertilization has led to concerns that pregnancies achieved using such methods may be at elevated risk of genetic anomalies.

STUDY DESIGN, SIZE, DURATION

For this prospective study, semen samples were collected from 45 infertile men.

PARTICIPANTS, SETTING, METHODS

Samples were assessed for DNA fragmentation using the Sperm Chromatin Dispersion Test (SCDt) and for chromosome abnormalities using multi-colour fluorescence in situ hybridization (FISH) with probes specific to chromosomes 13, 16, 18, 21, 22, X and Y. Additionally, both parameters were assessed simultaneously in 10 of the samples using a protocol combining SCDt and FISH.

MAIN RESULTS AND THE ROLE OF CHANCE

A significant correlation between the proportion of sperm with a numerical chromosome abnormality and the level of DNA fragmentation was observed (P < 0.05). Data from individual spermatozoa subjected to combined chromosome and DNA fragmentation analysis indicated that chromosomally abnormal sperm cells were more likely to display DNA damage than those that were normal for the chromosomes tested (P < 0.05). Not only was this association detected in samples with elevated levels of numerical chromosome abnormalities, but it was also evident in samples with chromosome abnormality rates in the normal range.

LIMITATIONS, REASONS FOR CAUTION

The inability to assess the entire chromosome complement is the main limitation of all studies aimed at assessing numerical chromosome abnormalities in sperm samples. As a result, some of the sperm classified as 'chromosomally normal' may be aneuploid for chromosomes that were not tested.

WIDER IMPLICATIONS OF THE FINDINGS

During spermatogenesis, apoptosis (a process that involves active DNA degradation) acts to eliminate abnormal sperm. Failure to complete apoptosis may explain the coincident detection of aneuploidy and DNA fragmentation in some spermatozoa. In addition to shedding light on the biological mechanisms involved in the processing of defective sperm, this finding may also be of clinical relevance for the identification of patients at increased risk of miscarriage or chromosomally abnormal pregnancy. In some instances, detection of elevated sperm DNA fragmentation may indicate the presence of chromosomal abnormalities. It may be worth considering preimplantation genetic screening (PGS) of embryos produced using such samples in order to minimize the risk of aneuploidy.

Genomic DNA in human blastocoele fluid

IVF often requires embryo cryopreservation through vitrification. During the vitrification process, the embryos can be collapsed by withdrawing the blastocoele fluid. The metabolomic profile of blastocoele fluid has been recently investigated by high-performance liquid chromatography-electrospray ionization-mass spectrometry to provide metabolite information that can help estimations of implantation efficiency. However, the presence of embryo DNA in blastocoele fluid has not been reported to date. This study shows using real-time PCR that genomic DNA was present in about 90% of blastocoele fluid samples harvested during the vitrification procedure. Moreover, the potential for determining embryo sex directly from blastocoele fluid is demonstrated by amplifying the multicopy genes TSPY1 (on the Y chromosome) and TBC1D3 (on chromosome 17). This opens up the possibility of screening embryos from couples carrying an X-linked disorder to identify male embryos at high risk of disease. The application of whole-genome amplification technologies to fluid samples is also shown to be feasible, potentially allowing more comprehensive genetic tests. As proof of principle, microarray comparative genomic hybridization was attempted to confirm the sex of embryos as well as detect several aneuploidies. However, further studies are needed to validate this approach and confirm that the accuracy is sufficient for diagnostic purposes.

48 QUIESCENCE INDUCES LONG-TERM EPIGENETIC CHANGES IN BOVINE FIBROBLASTS THAT IMPROVE THEIR REPROGRAMMING INTO CLONED ANIMALS

Cloning by somatic cell nuclear transfer (SCNT) forces cells to lose their lineage-specific epigenetic marks and become totipotent again. This reprogramming process often results in epigenetic and transcriptional aberrations that compromise development. Development rates after SCNT can thus serve as a functional assay for genome-wide epigenetic reprogramming. Dolly the sheep, the first mammalian SCNT clone, was derived from a donor cell that was induced into quiescence by serum starvation. We hypothesized that quiescence alters the epigenetic status of donor cells and elevates their reprogrammability. To test this idea, we compared chromatin composition and cloning efficiency of serum-starved quiescent (G0) bovine adult male fibroblasts versus non-starved, diploid G1 controls. Mechanically synchronized G1 cells were generated by manual selection or mitotic shake-off and processed within 3 h post-mitosis. Based on morphological assessment and 5-ethyl-2′-deoxyuridine (EdU) incorporation during continuous labelling, >93% of cells were captured in G1. Using quantitative confocal immunofluorescence microscopy and fluorometric enzyme-linked immunosorbent assay (ELISA), we show that G0 fibroblasts were significantly hypomethylated at lysines (K) of histone 3 (H3), specifically H3K4me3, H3K9me2, H3K9me3, and H3K27me3, but not H3K9me1. They were also significantly hypoacetylated at H3K9 and H4K5, hyperacetylated at H4K12, and unchanged at H4K16 positions. Furthermore, G0 cells significantly down-regulated the nuclear abundance of RNA polymerase II, histone variant H2A.Z, as well as polycomb group proteins EED, SUZ12, PHC1, and RING2. Following NT into metaphase-arrested oocytes, G0 chromatin condensed slower than that of G1 cells, indicating a more relaxed configuration. After 7 days of in vitro culture, H3K9me3, but not H4K4me3, H3K27me3, SUZ12, and RING2, remained hypomethylated in G0- versus G1-derived NT blastocysts, both in the inner cell mass and trophectoderm (730 v. 550 nuclei from 55 v. 42 G0 v. G1 blastocysts, respectively; n = 7 NT runs). Reduced H3K9me3 levels correlated with significantly increased mRNA abundance of the H3K9me3-specific histone demethylase KDM4B (or JMJD2B) in NT blastocysts. Expression of other pluripotency-related factors (NANOG, SOX2, STELLA, and IIFITM3), imprinted genes (SNRPN), and histone demethylases (KDM4A) was not affected in G0-derived blastocysts (32 G0 v. 55 G1 blastocysts; n = 4). Following NT, G0 donors developed significantly better into cloned blastocysts (175/382 = 46% v. 122/332 = 37% for G0 v. G1, respectively; n = 7, P < 0.05). Likewise, after transfer into surrogate mothers, G0-derived blastocysts developed significantly better into live calves (5/18 = 28% v. 1/25 = 4% for G0 v. G1, respectively; n = 2, P < 0.05). In conclusion, quiescence induced long-term epigenetic changes, specifically H3K9me3 hypomethylation, that correlated with increased donor cell reprogrammability. This research was supported by FRST C10X0303.

A method for semi-automatic grading of human blastocyst microscope images

BACKGROUND

The precise assessment of embryo viability is an extremely important factor for the optimization of IVF treatments. In order to assess embryo viability, several embryo scoring systems have been developed. However, they rely mostly on a subjective visual analysis of embryo morphological features and thus are subject to inter- and intra-observer variation. In this paper, we propose a method for image segmentation (the dividing of an image into its meaningful constituent regions) and classification of human blastocyst images with the aim of automating embryo grading.

METHODS

The delineation of the boundaries (segmentation) of the zona pellucida, trophectoderm (TE) and inner cell mass (ICM) were performed using advanced image analysis techniques (level set, phase congruency and fitting of ellipse methods). The fractal dimension and mean thickness of TE and ICM image texture descriptors (texture spectrum and grey-level run lengths) were calculated to characterize the main morphological features of the blastocyst with the aim of automatic grading using Support Vector Machine classifiers.

RESULTS

The fractal dimension calculated from the delineated TE boundary provided a good indication of cell number (presented a 0.81 Pearson correlation coefficient with the number of cells), a feature closely associated with blastocyst quality. The classifiers showed different accuracy levels for each grade. They presented accuracy ranges from 0.67 to 0.92 for the embryo development classification, 0.67-0.82 for the ICM classification and 0.53-0.92 for the TE classification. The value 0.92 was the highest accuracy achieved in the tests with 73 blastocysts.

CONCLUSIONS

Semi-automatic grading of human blastocysts by a computer is feasible and may offer a more precise comparison of embryos, reducing subjectivity and allowing embryos with apparently identical morphological scores to be distinguished.