Factors associated with premature chromosome condensation (PCC) following in vitro fertilization

Effects of failed oocyte activation and sperm protamine deficiency on fertilization post-ICSI

Sperm premature chromosomal condensation (PCC) has been associated with failed fertilization. Previous studies suggest that protamine deficiency or failed oocyte activation may make spermatozoa prone to PCC. However, it is not clear which of these two factors has a more profound effect on fertilization failure. In order to distinguish between these two phenomena, oocytes that failed to fertilize after intracytoplasmic sperm injection (ICSI) were artificially activated and the association between protamine deficiency and PCC was evaluated in the remaining oocytes that failed to fertilize. The results of this study reveal that after artificial activation, fertilization rate post-ICSI increased from 59.95 to 87.7% and PCC spermatozoa appeared to be present in over 50% of the remaining oocytes that failed to fertilize. The percentage of sperm PCC was significantly higher in protamine deficient samples, thus suggesting that after failed oocyte activation, sperm PCC induced by protamine deficiency may be considered as an alternative cause of failed fertilization post-ICSI. Furthermore, the results of this study did not show any correlation between pronuclei size asynchrony and protamine deficiency.

Can sperm protamine deficiency induce sperm premature chromosomal condensation?

Sperm premature chromatin condensation (PCC) has been considered as the second cause of failed fertilization post-intracytoplasmic sperm injection (post-ICSI). Cytoplasmic factors, including oocyte cytoplasmic immaturity have been suggested to induce PCC sperm. However, recent studies suggest that sperm chromatin anomaly might also lead to PCC sperm. During this study, human sperm from infertile patients with protamine deficiency or with adequate amount of protamine assessed by chromomycin A3 were injected into metaphase II mouse oocyte, treated with colcemid. Chromatin analysis was carried out on the injected oocyte. The results of this study show that contrary to the percentage of intact sperm, percentage of PCC sperm was significantly higher in oocytes injected with protamine deficient sperm (36.43 +/- 4.46) compared to oocytes injected with sperm with an adequate amount of protamine (11.99 +/- 3.54, P < 0.001). A significant correlation was also observed between percentage of PCC sperm and protamine deficiency (r = 0.46, P = 0.004). Therefore, it can be suggested that oocytes injected with protamine deficient sperm have a higher chance of forming PCC sperm and may result in failed fertilization post-ICSI.

The chromosomal analysis of human oocytes. An overview of established procedures

The cytogenetic survey of mature human oocytes has been and remains a subject of great interest because of the prevalence of aneuploidy of maternal origin in abnormal human conceptuses, and the lack of understanding about the non-disjunction processes in human meiosis. The first attempts to analyse the chromosomal content of human female gametes were made in the early 1970s, and led to limited data because of the paucity of materials and the inadequacy of the procedure used. The years to follow brought a resurgence of interest in this field, because of the development of human IVF techniques which made oocytes unfertilized in vitro available for cytogenetic analysis. Numerous studies have since been performed. However, the difficulties in obtaining good chromosome preparations and of performing accurate chromosome identification have reduced the viability of these studies, resulting in large variations in the reported incidences of chromosomal abnormalities. The further introduction of new procedures for oocyte fixation and the screening of large oocyte samples have allowed more reliable data to be obtained and to identify premature chromatid separation as a major mechanism in aneuploidy occurrence. The last decade has been privileged to witness the adaptation of molecular cytogenetic techniques to human oocytes, and thus various powerful procedures have been tried not only on female gametes, but also on polar bodies, involving sequential and multicolour fluorescent in situ hybridization (FISH) labelling, comparative genomic hybridization (CGH), spectral karyotyping and alternative methods such as primed in situ labelling (PRINS) and peptide nucleic acid (PNA) techniques. A large body of data has been obtained, but these studies also display a great variability in the frequency of abnormalities, which may be essentially attributable to the technical limitations of these in situ methods when applied to human oocytes. However, molecular cytogenetic approaches have also evidenced the co-existence of both whole chromosome non-disjunction and chromatid separation in maternal aneuploidy. In addition, the extension of these techniques to oocyte polar body materials has provided additional data on the mechanism of meiotic malsegregation. Improvements of some of these techniques have already been reported. The further development of new approaches for the in situ analysis of human meiosis will increase the impact of cytogenetic investigation of human oocytes in the understanding of aneuploidy processes in humans.

Relationship between protamine deficiency with fertilization rate and incidence of sperm premature chromosomal condensation post-ICSI

After aneuploidy, sperm premature chromatin condensation (PCC) is the next prevalent cause of fertilization failure. Therefore the aim of this study was to evaluate the effect of sperm protamine deficiency on sperm PCC formation post-ICSI. Chromatin analysis was carried out on failed fertilized oocytes post-ICSI and incidences of sperm PCC were evaluated and the results were compared with the extent of protamine deficiency assessed by chromomycin A3. The results show that incidence of sperm PCC was significantly different in failed fertilized oocytes injected from semen samples with greater or less than 30% CMA3 positivity (P = 0.04). However, except for fertilization rate (P < 0.001), the mean number of MII, MI and germinal vesicles oocytes and percentage normal sperm were not significantly different between the two groups (P > 0.05). A significant correlation was observed between sperm protamine deficiency with fertilization rate. Hence sperm protamine deficiency affects fertilization rate and possibly prones sperm to PCC post-ICSI.

Morphological and cytogenetic analysis of intact oocytes and blocked zygotes

We examined cytological and cytogenetic parameters of 1076 oocytes and 385 zygotes that failed to develop post in vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI). Out of 1076 oocytes, 894 (83%) arrested oocytes showed a first polar body and were thus assumed arrested at metaphase II while the remainder showed no polar body. In the group of oocytes with a polar body, 20.5% had an abnormal karyotype. Cytologically, premature sperm chromosome condensation was noted in 28.3% of uncleaved oocytes. This high PCC can be explained by the different grades of oocyte maturity from one center to another. Oocytes from older women showed no increased aneuploidy but did show increased premature chromosome condensation. Analysis by classical technique of 220 uncleaved zygotes showed 91 with highly condensed chromosomes, 53 with asynchrony of condensation, 31 with pulverized chromosomes, and 45 arrested at the first somatic metaphase. Out of 385 arrested zygotes, 165 were explored by in situ hybridization. FISH using a set of 7 chromosome-specific probes showed aneuploidy in the chromosomes analyzed (13, 16, 18, 21, 22, X, Y) in 21.8% of blocked zygotes (19-25% depending on morphology). Extrapolating to other chromosomes, we expect that a vast majority of blocked zygotes and oocytes probably carry chromosome abnormalities. These data demonstrate the contributions of chromosome disorder in early embryo development blocking and implantation failure. Certainly, the issue of cytoplasm and nuclear immaturity and their relation to each other and to chromosome abnormalities provides a fertile area for future investigation in ART.

Intracytoplasmic sperm injection could minimize the incidence of prematurely condensed human sperm chromosomes

OBJECTIVE

To compare the fertilization and prematurely condensed human sperm chromosomes (PCCs) rates between two intracytoplasmic sperm injection (ICSI) techniques.

DESIGN

A retrospective study.

SETTING

The data were obtained from the University of British Columbia in vitro fertilization (IVF) laboratory.

PATIENT(S)

ICSI cycles (n = 105) were performed for couples suffering from severe male-factor infertility and dysfunction of fertilization.

INTERVENTION(S)

Two types of ICSI techniques were used for ICSI procedures.

MAIN OUTCOME MEASURE(S)

Fertilization and pregnancy rates in group B using the improved ICSI technique were compared with those of group A using the standard ICSI technique. Unfertilized oocytes from the two groups were studied with cytogenetic methods.

RESULT(S)

Oocyte damage dropped from 14.8% in group A to 5.3% in group B. Normal fertilization for each group was 57.3% and 88.4%, respectively (P<.05). Pregnancy rate per egg retrieval was 15.6% in group A and 27.4% in group B (P<.05). PCCs occurred in 19.4% of unfertilized oocytes in group A and did not occur in group B.

CONCLUSION(S)

This study indicates that ICSI not only yields high fertilization rates, but also minimizes the incidence of PCCs. It may be directly related to two crucial steps (immobilization of sperm and aspiration of oocyte cytoplasm) used in ICSI procedures. This study also suggests that it is possible to overcome one cause of IVF failure resulting from the formation of PCCs by using the improved ICSI technique.

Effects of chilling to 0 degrees C on the morphology of meiotic spindles in human metaphase II oocytes

OBJECTIVE

To determine the effects of chilling to 0 degrees C on the meiotic spindle of human metaphase II oocytes, as observed by optical sectioning microscopy.

DESIGN

Laboratory study.

SETTING

Academic research laboratory in a medical school.

PATIENT(S)

Seventy-two women undergoing infertility treatment donated a total of 108 oocytes.

INTERVENTION(S)

Metaphase II oocytes were stripped of their cumulus cells, cooled directly to 0 degrees C, and held for periods of 1 to 10 minutes. They were then fixed at 37 degrees C, stained for immunofluorescence, and examined microscopically.

MAIN OUTCOME MEASURE(S)

Morphology of the meiotic spindle in chilled and control oocytes.

RESULT(S)

Microscopic evaluations of 46 chilled oocytes revealed various time-dependent changes in microtubules compared to 9 control oocytes. After 1 minute at 0 degrees C, spindle damage was negligible, but in oocytes cooled for 2 or 3 minutes, there was obvious shortening of the spindle and loss of polarity. Cooling to 0 degrees C for 4 to 9 minutes resulted in increasingly more drastic changes; by 10 minutes the spindles had totally disappeared. Despite depolymerization of microtubular tubulin at 0 degrees C, the chromosomes did not become dispersed, but remained anchored even in the absence of spindles.

CONCLUSION(S)

Even brief exposure of human oocytes to temperatures near 0 degrees C causes profound alterations of the meiotic spindle.

Development of embryos produced by intracytoplasmic sperm injection of cat oocytes

Development of cat oocytes following intracytoplasmic sperm injection (ICSI) and in vitro fertilization (IVF) was compared in two experiments. Domestic cat donors (used as a model for wild felids) were treated with 150 IU equine chorionic gonadotrophin (eCG) on treatment day 1 or a total of 10-15 IU of follicle-stimulating hormone (FSH) over four days, followed by 100 IU human chorionic gonadotrophin (hCG) on day 5 and follicular aspiration 24-26 h later. A jaguarundi (Herpailurus yaguarondi) female was stimulated twice with FSH (20 IU) or eCG (300 IU) and hCG (250 or 300 IU) before oocyte recovery. After storage at 4 degrees C, domestic cat semen was washed and processed. For ICSI, denuded oocytes were each injected with an immobilised spermatozoon. IVF oocytes were co-incubated with 5 x 10(4) motile spermatozoa/0.5 ml for 4-6 h. Noncleaving oocytes were fixed and stained 24-28 h after injection or insemination. Presumptive zygotes were cultured before transfer on day 5 (experiment I only) or evaluation on day 7 (experiments I and II). In experiment I, fertilization frequency was 67.9% (72/106) and 58.1% (122/210) for IVF and ICSI oocytes, respectively (P > 0.05). Most noncleaving ICSI oocytes (71/88, 80.7%) at 24 h were at metaphase II, of which half (35/71, 49.3%) had an activated spermatozoon (n=4) or premature chromatin condensation (PCC, n=31) of the sperm head. All 69 day 7 IVF embryos developed to morulae (> 16-cells, 46.7%) or blastocysts (53.3%), and 59/63 (93.7%) ICSI embryos reached the morula (50.8%) or blastocyst (42.9%, P > 0.05) stage. Mean cell number in IVF and ICSI embryos was 136 and 116 (P > 0.05); morulae had 77 and 46 (P < 0.05) and blastocysts had 187 and 209 (P > 0.05) cells, respectively. After transfer of 10 or 11 day 5 ICSI morulae to each of four recipients, a total of three kittens were born to two dams at 66 or 67 days. Of 18 fair-to-good quality oocytes recovered from a jaguarundi on two occasions, 10 (55.6%) embryos were produced by ICSI with fresh (n=5) or frozen (n=5) conspecific spermatozoa, but no jaguarundi kittens were born after transfer of these embryos to domestic cat recipients. In experiment II, cleavage frequency following IVF (15/17, 88.2%) and ICSI (31/38, 81.6%) was higher (P < 0.05) than following sham ICSI (13/35, 37.1%). Mean cell number (27 cells) and blastocyst development (0%) on day 7 was lower (P < 0.05) in the sham ICSI group than in the ICSI group (45 cells, 15.6% blastocysts) which, in turn, was lower (P < 0.05) than the IVF group (94 cells, 46.7% blastocysts). We have demonstrated that ICSI can be applied successfully in domestic felids and suggest that the technique will effectively augment other biotechniques being developed for enhancing reproduction in endangered felids.

Prematurely condensed chromosomes and meiotic abnormalities in unfertilized human oocytes after ovarian stimulation with and without gonadotropin-releasing hormone agonist

OBJECTIVE

To investigate the incidence of meiotic abnormalities, aneuploidy, and prematurely condensed sperm chromosomes in failed fertilized oocytes after controlled ovarian hyperstimulation (COH).

DESIGN

Retrospective analysis of air-dried preparations of unfertilized oocytes.

SETTING

University hospital-based infertility clinic.

PATIENT(S)

Thirty-three patients undergoing IVF having only tubal factor as the cause of infertility. Twelve patients (13 cycles) underwent treatment with hMG alone (-GnRH agonist [GnRH-a]), and 21 patients (24 cycles) underwent treatment with leuprolide acetate (LA) and hMG (+GnRH-a group).

INTERVENTION(S)

Standard IVF-ET treatment cycle for ovarian stimulation using hMG with or without LA.

MAIN OUTCOME MEASURE(S)

The meiotic stage, ploidy, and the presence of prematurely condensed sperm chromosomes were determined in 161 air-dried preparations of unfertilized oocytes.

RESULT(S)

Significantly more unfertilized oocytes were at metaphase II in the -GnRH-a group as compared with the +GnRH-a group, with significantly fewer exhibiting meiotic aberrations. Aneuploidy rates did not differ between groups. However, significantly more oocytes in the +GnRH-a group revealed prematurely condensed sperm chromosomes than in the -GnRH-a group.

CONCLUSION(S)

The use of GnRH-a for COH does not have an impact on aneuploidy rates in failed fertilized oocytes. However, the higher incidence of meiotic aberrations and prematurely condensed sperm chromosomes in the unfertilized population indicates that some retrieved oocytes exhibit incomplete nuclear and cytoplasmic maturation after the use of this agonist.

In vitro fertilization failure: identification of gamete defects by investigation of sperm-zona pellucida binding capacity of unfertilized oocytes

The objective of the study was to determine whether fertilization failure was due to spermatozoal or oocyte factors. Twenty-five unfertilized oocytes from 12 IVF/GIFT couples showing total or partial fertilization failure were evaluated for sperm zona binding potential under hemizonaeassay (HZA) conditions. Hemizonae were separately incubated with a sperm sample from the husband and that of a fertile control. Tight sperm binding to hemizonae was assessed. First, among the 12 patients, results showed a possible zona defect thought to be the cause of fertilization failure in five cases. Second, in two cases, fertilization failure was possibly caused by poor sperm binding potential of spermatozoa. Third, in two cases, fertilization failure was possibly caused by an oocyte defect, and fourth, three cases showed a mixture of possible causes. The results stress the need to develop a sequential analytic programme for those couples with repeated total or partial fertilization failure.

Cytogenetics of uncleaved oocytes and arrested zygotes in IVF programs

PURPOSE

Cytogenetic studies of arrested oocytes and zygotes were used to understand in vitro fertilization (IVF) failures.

METHODS

We investigated the cytogenetics (Giemsa banding and FISH) of 710 uncleaved oocytes and 94 arrested zygotes from 208 patients undergoing IVF procedures.

RESULTS AND CONCLUSIONS

Of uncleaved oocytes without a polar body, 39% were judged cytogenetically abnormal (17% unbalanced predivision and 21.5% diploid). Of 575 oocytes with a polar body, 124 (21.5%) showed numerical or structural chromosome aberrations. In arrested zygotes, approximately equal cases were found with separate condensed haploid complements (no syngamy), nuclear asynchrony and pulverized DNA, and apparently cytogenetically normal zygotes arrested at mitosis. These data on chromosome abnormalities were also analyzed with respect to two ovarian stimulation protocols and to maternal age. Both ovarian stimulation protocols and to maternal age. Both ovarian stimulation protocols showed the same levels of chromosome abnormalities. Overall chromosome abnormalities and premature chromosome condensation were also unchanged with maternal age. These data illustrate the significance of chromosome aberrations in IVF failures.

Chromosome studies in human unfertilized oocytes and uncleaved zygotes after treatment with gonadotropin-releasing hormone analogs

OBJECTIVE

To determine the frequency of the anomalies from the cytogenetic point of view in the oocytes remaining from our in vitro fertilization (IVF) program. Two gonadotropin-releasing hormone analogs (GnRH-a) were used (buserelin acetate and leuprolide acetate) in the superovulation treatment.

DESIGN

A prospective study was planned in January 1989. Deadline for data and quantitative analysis was to be July 1990.

SETTING

Hospital de Cruces, a public and tertiary institute.

PATIENTS

One hundred thirty-nine IVF patients, yielding 433 oocytes. Selected on the basis of availability of oocytes and staff.

RESULTS

Two hundred thirty-eight oocytes (71.25%) exhibited the normal number of metaphase II chromosomes; 64 (19.16%) exhibited aneuploidy; 13 (3.89%) were diploid, hyperdiploid, or hypodiploid; and 19 (5.68%) showed parthenogenetic activation. Of the 99 zygotes, 17 were polyploid and 48 showed prematurely condensed chromosomes, whereas in 31 cases the male and female pronuclei remained separate.

CONCLUSIONS

It would not appear that the rate of chromosomal anomalies is affected after pituitary suppression with GnRH-a.