Fluorescence in situ hybridization in diluted and flow cytometrically sorted boar spermatozoa using specific DNA direct probes labelled by nick translation

Challenges and Considerations during In Vitro Production of Porcine Embryos

Genetically modified pigs have become valuable tools for generating advances in animal agriculture and human medicine. Importantly, in vitro production and manipulation of embryos is an essential step in the process of creating porcine models. As the in vitro environment is still suboptimal, it is imperative to examine the porcine embryo culture system from several angles to identify methods for improvement. Understanding metabolic characteristics of porcine embryos and considering comparisons with other mammalian species is useful for optimizing culture media formulations. Furthermore, stressors arising from the environment and maternal or paternal factors must be taken into consideration to produce healthy embryos in vitro. In this review, we progress stepwise through in vitro oocyte maturation, fertilization, and embryo culture in pigs to assess the status of current culture systems and address points where improvements can be made.

Application of the FISH Technique to Visualize Sex Chromosomes in Domestic Cat Spermatozoa

Fluorescence in situ hybridization is a molecular cytogenetics technique that enables the visualization of chromosomes in cells via fluorescently labeled molecular probes specific to selected chromosomes. Despite difficulties in carrying out the FISH technique on sperm, related to the need for proper nuclear chromatin decondensation, this technique has already been used to visualize chromosomes in human, mouse, cattle, swine, horse, and dog spermatozoa. Until now, FISH has not been performed on domestic cat sperm; therefore, the aim of this study was to visualize sex chromosomes in domestic cat sperm. The results showed the presence of X and Y chromosomes in feline spermatozoa. The procedure used for sperm decondensation and fluorescence in situ hybridization was adequate to visualize chromosomes in domestic cat spermatozoa and, in the future, it may be used to determine the degree of chromosomal abnormalities in these gametes.

Classical, Molecular, and Genomic Cytogenetics of the Pig, a Clinical Perspective

The chromosomes of the domestic pig (Sus scrofa domesticus) are known to be prone to reciprocal chromosome translocations and other balanced chromosome rearrangements with concomitant fertility impairment of carriers. In response to the remarkable prevalence of chromosome rearrangements in swine herds, clinical cytogenetics laboratories have been established in several countries in order to screen young boars for chromosome rearrangements prior to service. At present, clinical cytogenetics laboratories typically apply classical cytogenetics techniques such as giemsa-trypsin (GTG)-banding to produce high-quality karyotypes and reveal large-scale chromosome ectopic exchanges. Further refinements to clinical cytogenetics practices have led to the implementation of molecular cytogenetics techniques such as fluorescent in-situ hybridization (FISH), allowing for rearrangements to be visualized and breakpoints refined using fluorescently labelled painting probes. The next-generation of clinical cytogenetics include the implementation of DNA microarrays, and next-generation sequencing (NGS) technologies such as DNA sequencing to better explore tentative genome architecture changes. The implementation of these cytogenomics techniques allow the genomes of rearrangement carriers to be deciphered at the highest resolution, allowing rearrangements to be detected; breakpoints to be delineated; and, most importantly, potential gene implications of those chromosome rearrangements to be interrogated. Clinical cytogenetics has become an integral tool in the livestock industry, identifying rearrangements and allowing breeders to make informed breeding decisions.

Sex Manipulation Technologies Progress in Livestock: A Review

Sex manipulation technologies allow predetermination of the sex of animal offspring by altering the normal reproductive process. In livestock production, the difference in type and gender can translate into significant economic benefits, including alleviation of severe food shortages. In livestock, however, the commercial application of sex manipulation technologies is currently available for cattle only. In this review, we described the brief history of sex manipulation, and the research progresses of common methods used in sex manipulation thus far. Information presented in this review can inform future studies on expanding the scope and use of sex manipulation technologies in livestock.

An immunological approach of sperm sexing and different methods for identification of X- and Y-chromosome bearing sperm

Separation of X- and Y-chromosome bearing sperm has been practiced for selection of desired sex of offspring to increase the profit in livestock industries. At present, fluorescence-activated cell sorter is the only successful method for separation of X- and Y-chromosome bearing sperm. This technology is based on the differences in DNA content between these two types of sperm and has been commercialized for bovine sperm. However, this technology still has problems in terms of high economic cost, sperm damage, and lower pregnancy rates compared to unsorted semen. Therefore, an inexpensive, convenient, and non-invasive approach for sperm sexing would be of benefit to agricultural sector. Within this perspective, immunological sperm sexing method is one of the attractive choices to separate X- and Y-chromosome bearing sperm. This article reviews the current knowledge about immunological approaches, viz., H-Y antigen, sex-specific antigens, and differentially expressed proteins for sperm sexing. Moreover, this review also highlighted the different methods for identification of X- and Y-sperm.

Chromosome Aberrations and Fertility Disorders in Domestic Animals

The association between chromosomal abnormalities and reduced fertility in domestic animals is well recorded and has been studied for decades. Chromosome aberrations directly affect meiosis, gametogenesis, and the viability of zygotes and embryos. In some instances, balanced structural rearrangements can be transmitted, causing fertility problems in subsequent generations. Here, we aim to give a comprehensive overview of the current status and future prospects of clinical cytogenetics of animal reproduction by focusing on the advances in molecular cytogenetics during the genomics era. We describe how advancing knowledge about animal genomes has improved our understanding of connections between gross structural or molecular chromosome variations and reproductive disorders. Further, we expand on a key area of reproduction genetics: cytogenetics of animal gametes and embryos. Finally, we describe how traditional cytogenetics is interfacing with advanced genomics approaches, such as array technologies and next-generation sequencing, and speculate about the future prospects.

Microfluidic single sperm entrapment and analysis

Selection of healthy spermatozoa is of crucial importance for the success rates of assisted reproduction technologies (ART) such as in vitro fertilization and intra-cytoplasmic sperm injection. Although sperm selection for ART procedures is predominantly based on sperm motility, successful fertilization is not predicted by good motility alone. For example, sperm characteristics such as the acrosome state and DNA integrity have shown significant impact on ART outcome. Although fertilization can be achieved with a single spermatozoon of high quality, current quality assessments are population-based and do not allow investigation of multiple sperm characteristics on a single spermatozoon simultaneously. In order to study sperm cells on the single cell level, we designed and characterized a PDMS microfluidic platform that allows single sperm entrapment. After spatially confining individual sperm cells within microfluidic cell traps, the cell viability, chromosomal content and acrosome state were studied. This platform is suitable for the analysis of individual sperm cells, which could be exploited for (non-invasive) sperm analysis and selection by impedance or Raman spectroscopy.

Sexing of dog sperm by fluorescence in situ hybridization

Effective preselection of sex has been accomplished in several species of livestock and also in humans using the flow cytometric sperm sorting method. A guaranteed high sorting accuracy is a key prerequisite for the widespread use of sperm sexing. The standard validation method is flow cytometric remeasurement of the DNA content of the sexed sperm. Since this method relies on the same instrument that produced the original sperm separation, it is not truly independent. Therefore, to be able to specifically produce either male or female offspring in the dog, we developed a method of direct visualization of sex chromosomes in a single sperm using fluorescence in situ hybridization (FISH) as a validation method. Denaturation of canine spermatozoa by immersion in 1 M NaOH for 4 min yielded consistent hybridization results with over 97% hybridization efficiency and a good preservation of sperm morphology. There was no significant difference between the theoretical ratio (50:50) and the observed ratio of X- and Y-chromosome-bearing spermatozoa in any of the three dogs. In addition, the mean purities of flow-sorted sex chromosomes in spermatozoa of the three dogs were 90.8% for the X chromosome fraction and 89.6% for the Y chromosome fraction. This sorting was evaluated by using the dual color FISH protocol. Therefore, our results demonstrated that the FISH protocol worked reliably for both unsorted and sexed sperm samples.

Microisolation and microcloning of bovine X-chromosomes for identification of sorted buffalo (Bubalus bubalis) spermatozoa

Flow-cytometry sorting technology has been successfully used to separate the X- and Y-chromosome bearing spermatozoa for production of sex-preselected buffalo. However, an independent technique should be employed to validate the sorting accuracy. In the present study, X-chromosomes of bovine were micro-dissected from the metaphase spreads by using glass needles. Then X-chromosomes were then amplified by PCR and labelled with Cy3-dUTP for use as a probe in hybridization of the unsorted and sorted buffalo spermatozoa -chromosome. The results revealed that 47.7% (594/1246) of the unsorted buffalo spermatozoa were positive for X- chromosome probe, which was conformed to the sex ratio in buffalo (X:Y spermatozoa=1:1); 9.6% (275/2869) of the Y-sorted buffalo spermatozoa and 86.1% (1529/1776) of the X-sorted buffalo spermatozoa showed strong X-chromosome FISH signals. Flow cytometer re-analysis revealed that the proportions of X- and Y-bearing spermatozoa in the sorted X and Y semen was 89.6% and 86.7%, respectively. There were no significant differences between results assayed by flow-cytometry re-analysis and by FISH in this study. In conclusion, FISH probe derived from bovine X- chromosomes could be used to verify the purity of X and Y sorted spermatozoa in buffalo.

Improving the efficiency of insemination with sex-sorted spermatozoa

The sorting of X- and Y-chromosome-bearing spermatozoa by flow cytometry is nowadays one of the most apt assisted-reproduction technologies in livestock production. Potential economic and biological benefits, as well as those related to easier management of herds, have been reported arising out of the application of this technique, especially in cattle. Yet, the sex-sorting procedure induces damage to spermatozoa, affecting their function and fertilizing ability. Different species present varying degrees of susceptibility to damage from the sorting process and each has its own requirements for sex-sorted insemination procedures. Thus, several new protocols and strategies have been designed for the handling of sorted spermatozoa, with the main objective of optimizing their fertilizing ability and the consequent application of flow-cytometric sex-sorting technology. This article reviews current advances in this technology, pointing out the components to be improved before this technology may be widely applied in different domestic species.

[Progress on methods for purity assessment of separated chromosome X- or Y-bearing sperm]

In this review of methods for purity assessment of isolated chromosome X- and Y-bearing sperm, we compared the principles, operating procedures, as well as pros and cons for various methods. We conclude that nested PCR of single sperm will become a conventional and popular method with lower costs, and the method will play a very important role in optimizing the X, Y sorting method, if the sensitivity and accuracy of the method can be increased and the testing time decreased, and promote the new progress in other genetic testing techniques on single sperm.

Chromosomal abnormalities, meiotic behavior and fertility in domestic animals

Since the advent of the surface microspreading technique for synaptonemal complex analysis, increasing interest in describing the synapsis patterns of chromosome abnormalities associated with fertility of domestic animals has been noticed during the past three decades. In spite of the number of scientific reports describing the occurrence of structural chromosome abnormalities, their meiotic behavior and gametic products, little is known in domestic animal species about the functional effects of such chromosome aberrations in the germ cell line of carriers. However, some interesting facts gained from recent and previous studies on the meiotic behavior of chromosome abnormalities of domestic animals permit us to discuss, in the frame of recent knowledge emerging from mouse and human investigations, the possible mechanism implicated in the well known association between meiotic disruption and chromosome pairing failure. New cytogenetic techniques, based on molecular and immunofluorescent analyses, are allowing a better description of meiotic processes, including gamete production. The present communication reviews the knowledge of the meiotic consequences of chromosome abnormalities in domestic animals.

An update on Reproductive Technologies with Potential Short-Term Application in Pig Production

Over the past decade, there has been an increase in the development and/or in the improvement of emerging reproductive technologies in pigs. Among emerging reproductive technologies with potential short-term application in pig production are: artificial insemination with low number of spermatozoa, cryopreservation of spermatozoa and embryos, sperm sexing, and non-surgical embryo transfer. The following review will give emphasis to recent advancements in these reproductive technologies that are starting to show possibilities of serious applications under field conditions.

Preselection of sex of offspring in swine for production: current status of the process and its application

It is estimated that as many as 30,000 offspring, mostly cattle, have been produced in the past 5 years using AI or some other means of transport with spermatozoa sexed by flow cytometric sperm sorting and DNA as the marker of differentiation. It is well documented that the only marker in sperm that can be effectively used for the separation of X- and Y-chromosome bearing spermatozoa is DNA. The method, as it is currently used worldwide, is commonly known as the Beltsville Sperm Sexing Technology. The method is based on the separation of sperm using flow cytometric sorting to sort fluorescently (Hoechst 33342) labeled sperm based on their relative content of DNA within each population of X- and Y-spermatozoa. Currently, sperm can be produced routinely at a rate of 15 million X- and an equal number of Y-sperm per hour. The technology is being applied in livestock, laboratory animals, and zoo animals; and in humans with a success rate of 90-95% in shifting the sex ratio of offspring. Delivery of sexed sperm to the site of fertilization varies with species. Conventional AI, intrauterine insemination, intra-tubal insemination, IVF with embryo transfer and deep intrauterine insemination are effectively used to obtain pregnancies dependent on species. Although sperm of all species can be sorted with high purity, achieving pregnancies with the low numbers of sperm needed for commercial application remains particularly elusive in swine. Deep intrauterine insemination with 50-100 million sexed boar sperm per AI has given encouragement to the view that insemination with one-fiftieth of the standard insemination number will be sufficient to achieve pregnancies with sexed sperm when specialized catheters are used. Catheter design, volume of inseminate, number of sexed sperm are areas where further development is needed before routine inseminations with sexed sperm can be conducted in swine. Cryopreservation of sex-sorted sperm has been routinely applied in cattle. Although piglets have been born from frozen sex-sorted boar sperm, freezing and processing protocols in combination with sex-sorted sperm are not yet optimal for routine use. This review will discuss the most recent results and advances in sex-sorting swine sperm with emphasis on what developments must take place for the sexing technology to be applied in commercial practice.