Detection of Y-bearing porcine spermatozoa by in situ hybridization using digoxigenin-labeled, porcine male-specific DNA probe produced by polymerase chain reaction

Generating porcine chimeras using inner cell mass cells and parthenogenetic preimplantation embryos

Background

The development and validation of stem cell therapies using induced pluripotent stem (iPS) cells can be optimized through translational research using pigs as large animal models, because pigs have the closest characteristics to humans among non-primate animals. As the recent investigations have been heading for establishment of the human iPS cells with naïve type characteristics, it is an indispensable challenge to develop naïve type porcine iPS cells. The pluripotency of the porcine iPS cells can be evaluated using their abilities to form chimeras. Here, we describe a simple aggregation method using parthenogenetic host embryos that offers a reliable and effective means of determining the chimera formation ability of pluripotent porcine cells.

Methodology/Significant Principal Findings

In this study, we show that a high yield of chimeric blastocysts can be achieved by aggregating the inner cell mass (ICM) from porcine blastocysts with parthenogenetic porcine embryos. ICMs cultured with morulae or 4–8 cell-stage parthenogenetic embryos derived from in vitro-matured (IVM) oocytes can aggregate to form chimeric blastocysts that can develop into chimeric fetuses after transfer. The rate of production of chimeric blastocysts after aggregation with host morulae (20/24, 83.3%) was similar to that after the injection of ICMs into morulae (24/29, 82.8%). We also found that 4–8 cell-stage embryos could be used; chimeric blastocysts were produced with a similar efficiency (17/26, 65.4%). After transfer into recipients, these blastocysts yielded chimeric fetuses at frequencies of 36.0% and 13.6%, respectively.

Conclusion/Significance

Our findings indicate that the aggregation method using parthenogenetic morulae or 4–8 cell-stage embryos offers a highly reproducible approach for producing chimeric fetuses from porcine pluripotent cells. This method provides a practical and highly accurate system for evaluating pluripotency of undifferentiated cells, such as iPS cells, based on their ability to form chimeras.

Determination of the correlation between stallion's age and number of sex chromosome aberrations in spermatozoa

The aim of this study was a cytogenetic analysis of stallions semen to find sex chromosome aberrations and to determine if there was an association between stallion's age and aberration frequency for the sex chromosomes. Sperm samples were collected from 22 stallions of various age from 3 to 23 years. Multicolour FISH was performed on each sample, using probes for the sex chromosomes and EGFR gene, localized on 4p12 in domestic horse. A total of 26199 sperm cells were analysed (from 1 070 to 1 532 per animal). Among the analysed cells, there were 50.318% with X chromosome, 48.543% with Y chromosome and 1.139% with aberrant chromosomes. The frequency of aberrations was: sex chromosomes nullisomy (0.466%), XY aneuploidy (0.454%), XX disomy (0.146%), YY disomy (0.041%), diploidy (0.024%) and trisomy XXY (0.008%). Additionally there was a correlation between the age of an animal and the frequency of sex chromosome aberration and a significant positive correlation between age and disomy of XY, XX, YY, trisomy of XXY, autosomal disomy was seen. A Correlation between the age of a stallion and the level of nullisomy was negative. The present study demonstrated that FISH technique is a powerful method to identify sex chromosome aberrations in equine spermatozoa and might be very helpful for a breeder during a selection for the best stallion.

Modification of equine sperm chromatin decondensation method to use fluorescence in situ hybridization (FISH)

Fluorescence in situ hybridization (FISH) is widely used in the study of chromosome structure and organization. Cytogenetic evaluation of chromosomes using FISH technique plays an increasingly important role in diagnosing karyotype changes in both somatic and reproductive cells. The aim of the study was to optimize the conditions of stallion sperm decondensation, which have a significant effect on the results of fluorescence in situ hybridization. Appropriate type and time of decondensation was chosen for the sperm of every stallion. It was found that decondensation performed using a preparation incubated in DTT solution for 1.5 minutes and in SDS solution for 10 seconds proved effective for stallions no. 1 and 2. An alternative decondensation method performed in an Eppendorf tube, with incubation in DTT solution for 1 minute and in SDS solution for 5 seconds proved effective for stallions no. 3 and 4. Decondensation using DTT and papain solution, a method successfully used for bull spermatozoa, proved inadequate for horse spermatozoa.

Dominant-negative mutant hepatocyte nuclear factor 1alpha induces diabetes in transgenic-cloned pigs

Pigs have been recognized as an excellent biomedical model for investigating a variety of human health issues. We developed genetically modified pigs that exhibit the apparent symptoms of diabetes. Transgenic cloned pigs carrying a mutant human hepatocyte nuclear factor 1alpha gene, which is known to cause the type 3 form of maturity-onset diabetes of the young, were produced using a combined technology of intracytoplasmic sperm injection-mediated gene transfer and somatic cell nuclear transfer. Although most of the 22 cloned offspring obtained died before weaning, four pigs that lived for 20-196 days were diagnosed as diabetes mellitus with nonfasting blood glucose levels greater than 200 mg/dl. Oral glucose tolerance test on a cloned pig also revealed a significant increase of blood glucose level after glucose loading. Histochemical analysis of pancreas tissue from the cloned pigs showed small and irregularly formed Langerhans Islets, in which poor insulin secretion was detected.

Expression of enhanced green fluorescent protein in porcine- and bovine-cloned embryos following interspecies somatic cell nuclear transfer of fibroblasts transfected by retrovirus vector

Interspecies somatic cell nuclear transfer (iSCNT) has emerged as an important tool for studying nucleo-cytoplasmic interactions and cloning of animals whose oocytes are difficult to obtain. This study was designed to explore the feasibility of employing transgenic fibroblasts as donor cells for iSCNT. The study examined the chromatin morphology, in vitro development, and expression of an enhanced green fluorescent protein (EGFP) gene in porcine- and bovine-cloned embryos produced by iSCNT of fetal fibroblast transfected with a pLNbeta-EGFP retroviral vector. Parthenogenetic and transfected or nontransfected intraspecies SCNT embryos were used as controls for comparison. Analysis of data revealed that xenogenic oocyte was able to reprogram somatic cells of different genus and supports their in vitro development to the blastocyst stage. However, the developmental rates of transgenic iSCNT embryos to the blastocyst stage were significantly lower than those of intraspecies SCNT embryos. The reduction in development rates was however, not due to integration of the transgene as the lower (P < 0.05) development rates of the intraspecies SCNT porcine or bovine embryos did not differ between transgenic and nontransgenic groups. Expression of EGFP was observed in 100% of blastocysts and mosaicism was not observed. Furthermore, after iSCNT of porcine or bovine donor nuclei into xenogenic ooplasm, patterns of nuclear remodeling in reconstructed embryos were similar. In conclusion, our data demonstrated the feasibility of producing transgenic iSCNT embryos. To our knowledge, this is the first report of transgenic cloned embryo production by iSCNT approach. In the future, this may provide a powerful research tool for studying developmental events in domestic animals and provide marked cell lines for other genetic manipulations.

Sexing river buffalo (Bubalus bubalis L.), sheep (Ovis aries L.), goat (Capra hircus L.), and cattle spermatozoa by double color FISH using bovine (Bos taurus L.) X- and Y-painting probes

River buffalo, sheep, and goat spermatozoa were cross-hybridized using double color fluorescence in situ hybridization (FISH) with bovine Xcen- and Y-chromosome painting probes, prepared by DOP-PCR of laser-microdissected-catapulted chromosomes, to investigate the possibility of using bovine probes for sexing sperm of other members of the family Bovidae. Before sperm analysis, the probes were hybridized on metaphase chromosomes of each species, as control. Frozen-thawed spermatozoa of cattle, river buffalo, sheep, and goat were decondensed in suspension with 5 mM DTT. Sperm samples obtained from three individuals of each species were investigated, more than 1,000 spermatozoa were scored in each animal. FISH analysis of more than 12,000 sperm revealed high level of sperm with X- or Y-signals in all of the species investigated, indicating FISH efficiency over 99%. Significant interspecific differences were detected in the frequency of aberrant spermatozoa (aneuploid and diploid) between goat (0.393%) and sheep (0.033%) (P < 0.01), goat and cattle (0.096%) (P < 0.5), as well as between river buffalo (0.224%) and sheep (P < 0.5). There was no significant difference between river buffalo and cattle. The present study demonstrated that it is possible to use bovine X-Y painting probes for sexing and analyzing sperm of other species of the family, thus facilitating future studies on the incidence of chromosome abnormalities in sperm as well as on sex predetermination of embryos for the livestock industry. Mol. Reprod. Dev. 67: 108-115, 2004.

Sex differentiation and germ cell production in chimeric pigs produced by inner cell mass injection into blastocysts

This study aimed at collecting background knowledge for chimeric pig production. We analyzed the genetic sex of the chimeric pigs in relation to phenotypic sex as well as to functional germ cell formation. Chimeric pigs were produced by injecting Day 6 or Day 7 inner cell mass (ICM) cells into Day 6 blastocysts. Approximately 20% of the piglets born from the injected blastocysts showed overt coat color chimerism regardless of the embryonic stage of donor cells. The male:female sex ratio was 7:2 and 6:1 in the chimeras derived from Day 6 and Day 7 ICM cells, respectively, showing an obvious bias toward males. When XX donor cells were injected into XY blastocysts at the same embryonic stage, the phenotypic sex of the resulting chimera was male with no germ-line cells formed from the donor cell lineage. On the other hand, when the donor was XY and the recipient blastocyst was XX, the phenotypic sex of the chimera was male, and germ-line cells were derived only from the donor cells. The combination of XY donor cells and XY blastocysts produced some chimeras in which the donor cell lineage did not contribute to germ-line formation even when it appeared in coat color. When the embryonic stage of the donor was advanced by 1 day in the XY-XY combination, 100% of the germ-line cells of the chimeras were derived from the donor cell lineage. These data showed that characteristics of sex differentiation and germ cell formation in chimeric pigs are similar to those in chimeric mice.

Sexing of porcine embryo by in situ hybridization using chromosome Y- and 1-specific DNA probes

This study was carried out to determine if a rapid, simultaneous detection system using chromosome Y- and 1-bearing boar spermatozoa was applicable for sexing embryos. Porcine embryos were recovered from gilts and sows 4 to 6 d after mating, and whole embryos or biopsy cells were mounted on a glass slide with a small amount of fixative (methanol: acetic acid: distilled water = 9:1:4). The samples were then stained by means of a fluorescence in situ hybridization (FISH) procedure developed specifically for the detection of Y-bearing spermatozoa. Hybridization was performed using digoxigenin (dig)-labeled chromosome Y- specific DNA, and biotin-labeled chromosome 1-specific DNA sequences were detected as a signal of FITC and Texas Red on nucleus visualized DAPI-stain. Proportions of whole embryos labeled with chromosome 1-probe were 17 and 97% at the 3 to 16 and > or = 32 cell stage, respectively. Of the 93 biopsied embryos analyzed by FISH, 85 embryos (91%) could be accurately classified as male or female. Of the 65 biopsied embryos, 60 embryos (92%) had a clear blastocoele and a inner cell mass after 48 h of culture in vitro, and these embryos were evaluated as available embryos. One out of 4 recipient gilts which received sexed embryos at transfer farrowed 12 piglets of the expected sex. The results of this study demonstrated that porcine embryos at the > or = 32 cell stage can be sexed within 2 h using the FISH method. Moreover further development of the FISH technique could make it an effective tool for the study of early porcine embryos and for the control of porcine sex.

Fluorescence in situ hybridization with Y chromosome-specific probe in decondensed bovine spermatozoa

This study was carried out to demonstrate bovine Y chromosome-bearing spermatozoa by rapid fluorescence in situ hybridization (FISH), using a digoxigenin (Dig)-labeled DNA probe specific to bovine Y chromosome. Before the FISH procedure, sperm heads were treated for decondensation with dithiothreitol (DTT) and glutathione (GSH) with or without heparin supplementation. Concentrations of either above 2 mM DTT or above 100 mM GSH induced swelling of the sperm head, which resulted in sufficient detection of the Y chromosome signal in sperm nuclei by rapid FISH (49.8 to 53.4%). When FISH was used with 2 mM DTT or 100 mM GSH on specimens from 7 sires, the rate of detection of the Y chromosome signal varied among sires (5.4 to 49.6%), especially that of the GSH treatment. Supplementation of GSH with heparin (100 U/mL), however, could induce reliable, repeatable detection of the Y chromosome signal in sperm nuclei of all the 7 sires (48.4 to 50.3%). These results show that in bovine spermatozoa decondensed with GSH and heparin, rapid FISH can detect Y chromosome-bearing spermatozoa.

Verification of flow cytometorically-sorted X- and Y-bearing porcine spermatozoa and reanalysis of spermatozoa for DNA content using the fluorescence in situ hybridization (FISH) technique

Flow cytometric sperm sorting based on X and Y sperm DNA difference has been established as the only effective method for sexing the spermatozoa of mammals. The standard method for verifying the purity of sorted X and Y spermatozoa has been to reanalyze sorted sperm aliquots. We verified the purity of flow-sorted porcine X and Y spermatozoa and accuracy of DNA reanalysis by fluorescence in situ hybridization (FISH) using chromosome Y and 1 DNA probe. Eight ejaculates from 4 boars were sorted according to the Beltsville Sperm Sexing method. Porcine chromosome Y- and chromosome 1-specific DNA probes were used on sorted sperm populations in combination with FISH. Aliquots of the sorted sperm samples were reanalyzed for DNA content by flow cytometry. The purity of the sorted X-bearing spermatozoa was 87.4% for FISH and 87.0% for flow cytometric reanalysis; purity for the sorted Y-bearing spermatozoa was 85.9% for FISH and 84.8% for flow cytometric reanalysis. A total of 4,424 X sperm cells and 4,256 Y sperm cells was examined by FISH across the 8 ejaculates. For flow cytometry, 5,000 sorted X spermatozoa and 5,000 Y spermatozoa were reanalyzed for DNA content for each ejaculate. These results confirm the high purity of flow sorted porcine X and Y sperm cells and the validity of reanalysis of DNA in determining the proportions of X- and Y-sorted spermatozoa from viewing thousands of individual sperm chromosomes directly using FISH.

Rapid and simultaneous detection of chromosome Y- and 1-bearing porcine spermatozoa by fluorescence in situ hybridization

This study was carried out to develop a rapid and simultaneous detection system of chromosome Y- and 1-bearing porcine spermatozoa by fluorescence in situ hybridization (FISH). Chromosome Y- and 1-specific DNA probes were produced by polymerase chain reaction with digoxigenin (Dig)- or biotin-dUTP. The hybridization probe mixture of labeled Y-chromosome and chromosome 1-specific DNA was applied to the preparation, immediately denatured at 75 degrees C for 8 min, hybridized for 5 min at 37 degrees C and overall FISH steps were done within a few hours. When double FISH with Dig-labeled chromosome Y-specific and biotin-labeled chromosome 1-specific probes was applied to sperm nuclei pretreated with dithiothreitol, the average of 50.9% of sperm nuclei had the Dig-signal, 99.2% of the sperm nuclei had the biotin-signal and the average of 0.3% of sperm nuclei showed no signal. The putative rate of Y-bearing spermatozoa ranged from 49.8% to 52.8% among 5 boars and the average putative rate of Y-bearing spermatozoa was 51.0%. The results indicated that a rapid and simultaneous FISH with chromosome Y- and 1-specific porcine DNA probes produced by PCR made possible more accurate assessment of Y-bearing porcine spermatozoa.