The parental origin of the distal pronucleus in dispermic human zygotes

The purpose of this investigation was to determine the parental origin of the pronucleus furthest from the second polar body (the distal pronucleus) in dispermic human zygotes. Intact dispermic embryos (n = 53) and those from which the distal pronucleus (n = 50) was removed at the zygote stage were biopsied after cleavage. Blastomeres were sexed using either coamplification of X and Y probes using a duplex polymerase chain reaction (PCR), or simultaneous fluorescence in situ hybridisation (FISH) with directly fluorochrome-labelled probes for chromosomes X, Y and 18. The ratio X/Y was determined in both groups of embryos by assessing a minimum of two blastomeres. If the pronuclei in dispermic zygotes are topographically in a fixed position, the X/Y ratio should change from 1:3 in dispermic embryos to 1:1 in enucleated ones. The ratio of embryos containing only an X chromosome and those with X as well as Y chromosomes in the intact dispermic zygotes was 1.0:2.3 which is similar to the theoretical ratio of 1:3. This ratio was 1.0:1.3 in dispermic zygotes from which the distal pronuclei were removed. This ratio is not significantly different from the 1:1 ratio based on a statistical analysis with a sample size of 50. These sex ratios would have been considered different if more than 200 enucleations had been performed. Although the ratio X/Y was altered following removal of distal pronuclei, suggesting frequent targeting of male pronuclei, accidental removal of the female pronucleus could not be excluded. This indicates that enucleation of dispermic zygotes could produce high yields of gynogenetic and androgenetic embryos for research purposes. Clinical application aimed at producing biparental zygotes may be hazardous, since mosaicism was common among enucleated embryos.

Sex determination of human embryos using the polymerase chain reaction and confirmation by fluorescence in situ hybridization

OBJECTIVE

To use fluorescence in situ hybridization to corroborate the polymerase chain reaction (PCR) preimplantation diagnosis of human embryos in three couples carrying a chromosome X-linked disease.

SETTING

Clinical and research IVF laboratories.

PATIENTS

Individuals undergoing preimplantation diagnosis.

RESULTS

Four ETs were performed in couples undergoing preimplantation diagnosis by multiplex PCR or fluorescence in situ hybridization, resulting in the birth of two normal female twins. The result of another is pending. A total of 22 embryos were analyzed by PCR. Embryos that were diagnosed as being at risk of carrying the genetic abnormality (n = 8), embryos that failed diagnosis (n = 4), and genetically normal embryos that arrested development (n = 4) were further analyzed by fluorescence in situ hybridization. The sex of all 16 embryos was determined and confirmed the previous 12 preimplantation diagnoses by multiplex PCR. In addition, fluorescence in situ hybridization analysis allowed the detection of two aneuploid embryos, one XO and one XXY, previously diagnosed by PCR as a normal female and male. Two mosaics were also detected.

CONCLUSION

Polymerase chain reaction and fluorescence in situ hybridization are possible for preimplantation sex determination in cases of genetic sex-linked disease. Fluorescence in situ hybridization, however, supplies additional information about sex chromosome aneuploidy and is not susceptible to contamination or misdiagnosis of monosomy X.

Origin of single pronucleated human zygotes

PURPOSE

Diploidy in embryos developing from single pronucleated zygotes can occur following parthenogenetic activation or by asynchronous inflation of pronuclei following fertilization. To distinguish between these two mechanisms, sexing was performed.

RESULTS

The presence of a Y chromosome in the embryo was considered proof that fertilization had occurred. Twenty-one dividing embryos originating from single pronucleated zygotes were analyzed using the polymerase chain reaction or fluorescence in situ hybridization. In total, 43% (9/21) of the embryos showed Y chromosomes.

CONCLUSION

It can be extrapolated that more than 80% of them originated from fertilized eggs.

Sex distribution in arrested precompacted human embryos

Evidence of sexual dimorphism before fetal gonadal differentiation in mammals has been accumulating, suggesting that male embryos develop faster than female ones. The current investigation was performed to evaluate whether the development rate of precompacted human embryos is controlled by sex chromosomes. Sex was determined by polymerase chain reaction and fluorescence in situ hybridisation in 172 arrested embryos derived from in vitro fertilisation. The sex ratio (1.02:0.98) did not differ significantly from 1:1. Although more males appeared to have greater fragmentation, the difference between the sex ratios of highly fragmented and normal embryos (1.08:0.92) was not significant. Arrested female embryos had a tendency to exhibit more than five nuclei and less than 10% fragmentation, but the trend was not statistically significant. The current results suggest that the first developmental block in human embryos occurs prior to and shortly after genomic activation and is not determined by the presence of the Y chromosome.

[The main factors influencing the toxicity of Chinese materia medica]

This paper discusses the main factors influencing the toxicity of Chinese materia medica in respect of compatibility, dosage, processing, drug form, decoction preparation and channel of administration, then proceeds to expound the different ways these factors influence the toxicity of Chinese materia medica, mainly increasing, reducing, producing and accumulating toxicity, and thus provides theoretical basis for clinical rational administration of Chinese materia medica.

Preimplantation genetic diagnosis. In situ hybridization as a tool for analysis

In situ hybridization allows one to directly visualize DNA sequences of interest for which probes are available. Fluorescent signals can be detected in single cells in either metaphase or interphase nuclei, thus obviating the need for cell synchronization. The potential to use this technology in conjunction with in vitro fertilization techniques to genetically analyze an embryo before transfer could offer patients at genetic risk an alternative. Currently, these patients wait until 9 to 16 weeks' gestation to find out about the genetic makeup of their pregnancy. As such, sexing the embryos of patients at risk for transmitting sex-linked disorders or for performing numerical chromosome analysis could be performed before embryo transfer. Techniques for applying in situ hybridization to single cells obtained from embryos are presented. Hybridization of specific probes to blastomeres of mouse and human embryos as well as sperm is demonstrated.

Evaluation of Vero cell co-culture system for mouse embryos in various media

Our objective was to evaluate and compare the efficacy and mechanisms of co-culturing mouse embryos with Vero cells in both Dulbecco's modified Eagle's medium/Ham's F12 (DMEM/F12) and human tubal fluid (HTF) culture medium. Two-cell CB6F1 mouse embryos were cultured either in the presence of Vero cells (group A) or in culture medium alone (group B). In DMEM/F12 significantly more morulae developed in group A than in group B on day 3 (91 versus 23%; P less than 0.01). In contrast, the mouse embryos grew rapidly in HTF and significant differences were noted only in later embryonic stages (on day 5; 86% and 50%, P less than 0.01 of group A and B respectively, hatching or hatched). Similar experiments using DF1 and ICR mouse strains also revealed enhanced embryo development in the presence of Vero cells. To determine whether the embryo-enhancing effects of Vero cells were due to the removal of toxins or to the secretion of embryotrophic factors, ICR mouse embryos were cultured in fresh media with cells (group A), without cells (group B) and in cell-free conditions using cell-conditioned media which were obtained in the presence (group C) or absence (group D) of embryos. These results demonstrated that completion of hatching was highest (52%; P less than 0.01) in group A after 6 days in culture. There were no significant differences between groups B, C and D (rates of total hatching 18, 17 and 17%, respectively). It is concluded that Vero cells improve the development of mouse embryos and this is likely to be due to removal of substances inhibitory to development.(ABSTRACT TRUNCATED AT 250 WORDS)