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.

Dual labeling of the cytoskeleton and DNA strand breaks in porcine embryos produced in vivo and in vitro

In vitro-produced embryos exhibit decreased cell numbers, small inner cell masses and reduced pregnancy rates after transfer. Evaluation of intracellular components of in vitro-produced or -manipulated embryos will lead to improved methodology for embryo production. Whole mount techniques were developed to utilize terminal deoxynucleotidyl-transferase 3' nick end labeling (TUNEL) to detect broken DNA. Subsequent labeling of either tubulin or actin filaments provides further evidence of cytological damage. Porcine embryos produced in vitro or in vivo were evaluated throughout the cleavage and preimplantation stages of development. Early cleavage stages up to the 8-cell stage never contained TUNEL-labeled nuclei. However, TUNEL labeling of in vitro-produced morula revealed some blastomeres with broken DNA. Nearly all in vitro-produced blastocysts displayed some TUNEL positive cells, whereas in vivo-collected embryos at a similar stage displayed few, if any, TUNEL-labeled nuclei. The ratio of TUNEL-labeled DNA to total DNA area of in vitro-derived blastocysts was significantly greater than their in vivo counterparts (P < 0.05). Microtubule and microfilament labeling identified blastomeres of unequal size and shape that were losing cellular integrity. These data suggest that the combination of these labeling techniques may be useful in evaluating cellular damage in embryos produced under in vitro conditions.

The diversity of lipases from psychrotrophic strains of Pseudomonas: a novel lipase from a highly lipolytic strain of Pseudomonas fluorescens

Strains of Pseudomonas fluorescens and Ps. fragi are the predominant psychrotrophs found in raw milk and may cause spoilage due to the secretion of hydrolytic enzymes such as lipase and protease. The diversity of lipases has been examined in Pseudomonas isolates from raw milk which represent different taxonomic groups (phenons). Significant diversity was found using both DNA hybridization and immunoblotting techniques, which has implications for the development of a diagnostic test. The lipase-encoding gene (lipA) was cloned from one strain, C9, of Ps. fluorescens biovar V. In contrast to previously reported lipase sequences from Ps. fluorescens, the gene encodes a lipase of M(r) 33 kDa. Alignment of all known Pseudomonas and Burkholderia lipase amino acid sequences indicates the existence of two major groups, one of M(r) approximately 30 kDa comprising sequences from Ps. fragi, Ps. aeruginosa, Ps. fluorescens C9 and Burkholderia, and one of approximately 50 kDa comprising Ps. fluorescens lipases. The lipase from C9 does not contain a signal peptide and is presumed to be secreted via a signal peptide-independent pathway. The lipA gene of strain C9 was disrupted by insertional mutagenesis. The mutant retained its lipolytic phenotype, strongly suggesting the presence of a second lipase in this strain.

Comparative motility of X and Y chromosome-bearing bovine sperm separated on the basis of DNA content by flow sorting

A combination of flow cytometric sperm sorting of X and Y chromosome-bearing sperm (X and Y sperm) and computer-assisted sperm analysis (CASA) for measuring sperm motility allows assessment of motion parameters in the two populations. Bull sperm were separated into X and Y populations by flow cytometry following staining with the DNA-binding dye Hoechst 33,342. The motion parameters differed depending on sperm concentration. Decreasing sperm concentration resulted in higher velocities and straighter trajectories. The concentrations of control (stained-unsorted and unstained-unsorted) and flow-sorted sperm were therefore adjusted to similar numbers (5 x 10(6) sperm per milliliter). Samples of sorted X and Y sperm and control sperm were transferred to prewarmed slides on a heated stage (37 degrees C) and their motion video recorded for 2 min using a magnification of x 100 and a high-resolution camera. The sperm analysis was carried out on a Hobson Sperm Tracker (HST) using HST 7 software. The following motion parameters were measured: curvilinear, straight-line, and average path velocity; mean angular displacement (MAD); beat cross-frequency; amplitude of lateral head displacement; linearity (LIN); and straightness of path (STR). Sperm movement was unaffected by staining with Hoechst 33,342, excitation by ultraviolet (UV) light, or the physical process of cell sorting. Significant differences were seen between X and Y sperm for MAD, LIN, and STR. No difference was observed for the other parameters. The results indicate that in a simple salts solution, Y bull sperm do not swim faster than X sperm but may be distinguished from X sperm on the basis of LIN and STR.

Advances in gender preselection in swine

Gender preselection using isolated populations of X- and Y-chromosome bearing spermatozoa that have been separated on the basis of DNA content is currently possible in swine and other farm animals, as well as in humans. Semen from most livestock species can now be successfully separated into predominantly X or Y sperm populations before their use for intra-tubal insemination, deep-uterine insemination or for in vitro fertilization (IVF) to produce sexed offspring. Birth of progeny of the desired sex in cattle, sheep and swine under semi-practical conditions has successfully validated the sexing technology. Spermatozoa are separated on the basis of inherent differences in DNA content in the X- and Y-chromosome bearing sperm population using modified flow cytometry/cell sorting technology. Spermatozoa are stained with Hoechst 33342 which binds to the DNA in an amount proportional to the amount of DNA present in the individual spermatozoa. Over 300 animals from various species at several locations have been born using the USDA-Beltsville Sperm Sexing Technology for separating X and Y spermatozoa. Sex ratios are shifted from the normal 50:50 to 85 to 90% of one sex or the other. In swine, offspring have been born as the result of surgical intratubal insemination of separated spermatozoa and also from IVF and embryo transfer. At the present time, standard swine artificial insemination techniques are not optimized for use with the small numbers of flow cytometrically separated X or Y sperm populations. Cattle, swine and rabbit offspring have been reproduced through the second generation with normal morphology and reproductive function. Numerous improvements have been made in the sexing technology since it was first reported in 1989. Increasing the speed of the sexing process to make the application of the technology available to a larger segment of the livestock industry is paramount, even with insemination technology designed for small numbers of spermatozoa.

Engineering the healing of the rabbit medial collateral ligament

A biological approach to improve healing of the medial collateral ligament (MCL) was investigated by exploring the use of therapeutic growth factors based on in vitro and in vivo experiments. The in vitro cell culture studies involved screening a variety of growth factors to select those that exhibit the most positive effects on cell proliferation and extracellular matrix synthesis. The selected growth factors were applied in vivo to a rabbit model where the MCL was ruptured. Biomechanical and histological evaluations are performed to determine whether the selected growth factors can enhance the properties of the healed MCL, whether these improvements are dose dependent, and whether combinations of growth factors can enhance MCL healing to a greater extent than individual growth factors. In vitro studies showed that epidermal growth factor (EGF) and platelet derived growth factor-BB (PDGF-BB) have the greatest effect on ligament fibroblast proliferation, whereas transforming growth factor-beta 1 (TGF-beta 1) superiorly promotes extracellular matrix synthesis. These growth factors were then applied in vivo at different dosages, in isolation and in combination, and the ligaments were evaluated six weeks post-operatively. Tensile testing of the femur-MCL-tibia complexes (FMTCs) revealed that the specimens treated with a high dose of PDGF-BB have ultimate load, ultimate elongation and energy absorbed to failure values that are significantly greater than those from the other groups. The high dose of PDGF-BB was more effective than the low dose, indicating a dose dependency. The addition of TGF-beta 1 to PDGF-BB did not lead to any further increases in the structural properties of the FMTC. These encouraging results suggest that PDGF-BB may be a potential growth factor to enhance the quality of the healing ligament.

A 2.5-Mb transcript map of a tumor-suppressing subchromosomal transferable fragment from 11p15.5, and isolation and sequence analysis of three novel genes

11p15.5 is an important tumor-suppressor gene region, showing loss of heterozygosity in Wilms tumor, rhabdomyosarcoma, adrenocortical carcinoma, and lung, ovarian, and breast cancer. We previously mapped directly by genetic complementation a subtransferable fragment (STF) harboring an embryonal tumor-suppressor gene and spanning about 2.5 Mb. We have now mapped the centromeric end of this STF between D11S988 and D11S12 and its telomeric end between D11S1318 and TH. We have isolated a complete contig of PAC, P1, BAC, and cosmid genomic clones spanning the entire 2.5-Mb region defined by this STF, as well as more than 200 exons from these genomic clones using exon trapping. We have isolated genes in this region by directly screening DNA libraries as well as by database searching for ESTs. Nine of these genes have been reported previously by us and by others. However, the initial mapping of most of those genes was based on FISH or somatic cell hybrid analysis, and here we precisely define their physical location. These genes include RRM1, GOK (D11S4896E), Nup98, CARS, hNAP2 (NAP1L4), p57KIP2 (CDKN1C), KVLQT1 (KCNA9), TAPA-1, and ASCL2. In addition, we have identified several novel genes in this region, three of which, termed TSSC1, TSSC2, and TSSC3, are reported here. TSSC1 shows homology to Rb-associated protein p48 and chromatin assembly factor CAF1, and it is located between GOK and Nup98. TSSC2 is homologous to Caenorhabditis elegans beta-mannosyl transferase, and it lies between Nup98 and CARS. TSSC3 shows homology to mouse TDAG51, which is implicated in FasL-mediated apoptosis, and it is located between hNAP2 and p57KIP2. Thus, these genes may play a role in malignancies that involve this region.

Geriatric patient simulations for dental hygiene

The rapidly increasing number of this country's elderly requires that dental hygiene students practice the clinical problem-solving skills of information gathering, assessment, and treatment applied to geriatric patients. Computer-based simulations are purported to provide this experience, but little research has been completed with simulations in the education of dental hygienists. This paper summarizes the process used to design, develop, and evaluate a series of eighteen computer-based geriatric simulated patients. It contains a brief description of the simulations and a description of the design, validation, authoring, and formative evaluation phases. The paper also describes the summative evaluation, provides implementation suggestions, and summarizes future directions. The summative evaluation, conducted at four institutions, suggests that computer-based simulations are an effective instructional method as measured by pre/post-tests. The results suggest that simulations can provide a standardized set of geriatric patient experiences. These simulations may prove especially valuable at institutions that are unable to provide clinical geriatric experiences or lack the expertise to conduct a didactic course in geriatrics.

Membrane status of boar spermatozoa after cooling or cryopreservation

This study tested the hypothesis that sperm membrane changes during cooling contribute substantially to the membrane damage observed after cryopreservation of boar spermatozoa. Flow cytometry was used to assess viability (percentages of live and dead cells) of boar sperm cells after staining with SYBR-14 and propidium iodide (PI) and acrosome status after staining with FITC-pisum sativum agglutenin and PI. Incubation (38 degrees C, 4 h), cooling (to 15 or 5 degrees C) and freezing reduced the proportion of live spermatozoa compared with those in fresh semen. There were more membrane changes in spermatozoa cooled to 5 degrees C than to 15 degrees C. The proportion of live spermatozoa decreased during processing for cryopreservation and cooling to 5 degrees C, but was unaffected by freezing and thawing if held at 15 degrees C for 3.5 h during cooling. Spermatozoa not held during cooling exhibited further loss of viability after freezing and thawing. Holding the spermatozoa also increased the proportion of acrosome-intact spermatozoa at both 15 degrees C and 5 degrees C and at thawing compared with that of the unheld controls. The results of this study suggest that a substantial proportion of the membrane changes associated with cryopreservation of boar spermatozoa may be attributed to the cooling of the cells to 5 degrees C rather than to the freezing and thawing process, and that sperm membrane changes are reduced when semen is held at 15 degrees C during cooling.

Effectiveness of computer-aided removable partial denture design

PURPOSE

Computer programs have been developed for removable partial denture (RPD) design, but their educational impact has never been investigated. This study measured the effectiveness of computer-based RPD design simulations in a traditional RPD design course for second-year dental students.

MATERIALS AND METHODS

Thirty-six students were randomly assigned to four groups, two simulation and two control groups, at the beginning of the RPD design module. A cross-over design compared the two strategies during laboratory exercises. First, the simulation group worked with the simulation, while the control group met in small-group seminars with faculty. Post-test 1 was given, and then students switched teaching methods and post-test 2 was given. Each post-test had two parts. Part 1 involved designing an RPD based on specific patient criteria. Part 2 involved choosing the more correct of the two designs.

RESULTS

Results showed a significant difference (p = .0072) in two of four test groups. Although it was an initial evaluation, the computer simulation was shown to be equivalent to faculty-led small-group seminars. Students also responded positively to a questionnaire on their perceived effectiveness of the simulations.

CONCLUSIONS

The results suggest that RPD design can be taught as effectively with computer-based simulations as with faculty-led seminars.

Improving cardiopulmonary resuscitation skills retention: effect of two checklists designed to prompt correct performance

Previous research has shown that regardless of an individual's experience, life support skills such as cardiopulmonary resuscitation (CPR) are poorly performed as soon as 1 month following training. The purpose of this study was to compare the effects of two checklists designed to prompt correct CPR performance. We compared the performance of 169 undergraduate students, at the time of course assessment, with retention testing that occurred 2 months following the course assessment. Students were randomly assigned to a control group, a short version of a CPR checklist and a longer more detailed version. Two groups of variables were created: procedural and compression-ventilation variables. In addition, an overall-performance variable was created, summarizing performance on the procedural variables. Binary variables were assessed with chi 2-tests of independence. One-way ANOVAs, using 'group' as the between-subjects factor, were used to assess each continuous variable. Comparisons between groups yielded significant differences of P < 0.05. The long checklist generally led to superior performance on the procedural variables. The results support the hypothesis that remembering the steps of CPR is too complex for some. Though preliminary, the findings of this study indicate that the detailed checklist was an effective strategy to improve the post-course performance of CPR.

Production of piglets preselected for sex following in vitro fertilization with X and Y chromosome-bearing spermatozoa sorted by flow cytometry

In vivo-matured porcine oocytes were fertilized in vitro with X and Y chromosome-bearing spermatozoa, and sorted for sex on the basis of DNA content by flow cytometry. Developmental competence of the sexed embryos was determined through established pregnancies after embryo transfer. Spermatozoa were stained with Hoechst 33342 and sorted using a flow cytometry cell sorter. Purity of sorting was 83% for Y spermatozoa and 92% for X spermatozoa. A total of 387 mature cumulus-oocyte-complexes (COC) was collected from 18 superovulated prepuberal gilts shortly before ovulation. In vitro fertilization with sorted spermatozoa was performed in 4 replicates. After 18 h of sperm- oocyte co-culture at 39 degrees C, the zygotes were placed into culture medium (NCSU-23) for another 24 h. The average cleavage rate was 56.2%. Ninety-two embryos produced from X-sorted sperm cells were transferred surgically into the uterus of 2 recipients. Two gilts farrowed and delivered 6 and 4 healthy female piglets, respectively. Additionally, 2 gilts were inseminated intratubally via surgical laparotomy with either X or Y sorted spermatozoa (2 x 10(5)) per oviduct. The 2 sows farrowed producing 15 piglets. Thirteen of the 15 piglets were of the predicted gender (85%).

Chlortetracycline analysis of boar spermatozoa after incubation, flow cytometric sorting, cooling, or cryopreservation

In this study, the effects of staining procedure with chlortetracycline (CTC) and method of analysis of boar spermatozoa after staining were examined. The hypothesis that incubation, flow cytometric sorting, cooling, and cryopreservation cause changes to boar sperm membranes which resemble capacitation and the acrosome reaction was also tested. Membrane status was evaluated by flow cytometry and by fluorescence microscopy after staining with CTC, and acrosome integrity was checked by flow cytometry after staining with FITC-pisum sativum agglutenin and propidium iodide (PI). Flow cytometry was also used to assess viability (percentages of live and dead cells) of boar sperm after staining with SYBR-14 and PI. Staining of spermatozoa with CTC alone and in combination with PI and/or Hoechst 33342 had no effect on the proportion of spermatozoa allocated to the F (uncapacitated), B (capacitated), or AR (acrosome-reacted) CTC fluorescent staining categories. The mean percentages of acrosome-intact and acrosome-reacted cells were 88.4 and 6.8 or 0.8 and 96.5 in semen treated with 0 or 100 microg/ml lysophosphatidylchloine (LPC), respectively (P < 0.001). Most spermatozoa were also in the AR CTC-stained category after treatment with LPC compared with a small proportion in the controls. Using flow cytometry to examine sperm suspensions stained with CTC, a gated population of spermatozoa with low fluorescence (population 1) comprised predominantly F-pattern cells (F-pattern: population 1 vs. population 2, 80.5 vs. 14.4%; P < 0.001), whereas population 2 (high fluorescence) comprised mainly B-pattern cells (B-pattern: population 1 vs. population 2, 8.5 vs. 62.3%; P < 0.001). Incubation (38 degrees C, 4 hr), flow sorting, cooling (to 15 or 5 degrees C) and freezing reduced the proportion of F-pattern and live spermatozoa, and increased the proportion of B-, AR-pattern, and dead spermatozoa, in comparison with fresh semen. There were more membrane changes in spermatozoa cooled to 5 degrees C (30.4, 48.5, 21.1%) than in those cooled to 15 degrees C (56.1, 32.6, 11.5% F-, B-, and AR-pattern spermatozoa, respectively).

Human KVLQT1 gene shows tissue-specific imprinting and encompasses Beckwith-Wiedemann syndrome chromosomal rearrangements

Genomic imprinting is an epigenetic chromosomal modification in the gamete or zygote causing preferential expression of a specific parental allele in somatic cells of the offspring. We and others have identified three imprinted human genes on 11p15.5, IGF2, H19, and p57KIP2, although the latter gene is separated by 700 kb from the other two, and it is unclear whether there are other imprinted genes within this large interval. We previously mapped an embryonal tumour suppressor gene to this region, as well as five balanced germline chromosomal rearrangement breakpoints from patients with Beckwith-Wiedemann syndrome (BWS), a condition characterized by prenatal overgrowth and cancer. We isolated the upstream exons of the previously identified gene KVLQT1, which causes the familial cardiac defect long-QT (LQT) syndrome. We found that KVLQT1 spans much of the interval between p57KIP2 and IGF2, and that it is also imprinted. We demonstrated that the gene is disrupted by chromosomal rearrangements in BWS patients, as well as by a balanced chromosomal translocation in an embryonal rhabdoid tumour. Furthermore, the lack of parent-of-origin effect in LQT syndrome appears to be due to relative lack of imprinting in the affected tissue, cardiac muscle, representing a novel mechanism for variable penetrance of a human disease gene.

A computer program to aid in visual concept development in dentistry

Beginning dental students normally receive their first exposure to the study of tooth forms (morphology) through a dental anatomy laboratory course in which they are required to reproduce tooth morphology, usually with wax. The fabrication of a tooth in wax requires proper visual recognition skills and fine eye-hand coordination. Many students struggle with one or both of these. A computer program, designed to teach recognition concepts, was delivered to three groups of beginning freshman dental students in conjunction with their dental anatomy laboratory course while a group of their classmates served as the controls. This study investigated (1) instructional design and interface improvement and (2) the best method to implement the computer program. Experimental and control groups all received normal daily critiques of their course project work. After completion of the computer program, all groups were tested with a recognition-based examination as well as with a practical examination, requiring the reproduction of a tooth in wax. All experimental groups scored better than the control group on both examinations. Results indicated that computer-based instruction may be a useful means to foster visual concept development. An expanded program, using better graphics, animation and movies is currently under development.

Comparative viability of bovine sperm frozen on a cryomicroscope or in straws

The accuracy and repeatability of freezing rates and effects of evaporation were examined using a new cryomicroscope system to establish its usefulness in assessing the development of cryopreservation protocols for bovine semen. Post-thaw sperm plasma membrane integrity, as assessed by using combinations of fluorescent stains and flow cytometry, was used in evaluating protocols for freezing spermatozoa on the cryomicroscope. Semen was diluted in Test-yolk (20%) extender containing 7% glycerol and frozen in 0.5-ml straws, 0.25-ml straws (over liquid nitrogen for 8 min) or in a quartz crucible using a Linkam BCS 196 cryomicroscope. Thawed samples were diluted with Hepes buffered medium containing 0.1% bovine serum albumin (BSA) and stained with either carboxymethylfluorescein diacetate (CMFDA) or SYBR-14 each in combination with propidium iodide (PI). Flow cytometry analysis of the samples revealed 2 major populations: 1) spermatozoa with intense green fluorescence (stained with CMFDA or SYBR-14), which were classified as plasma membrane-intact and 2) spermatozoa with intense red fluorescence, (stained with PI), which were classified as plasma membrane-damaged. Samples frozen using the cryomicroscope contained 29 and 26 % plasma membrane-intact (PMI) sperm cells, as assessed by CMFDA and SYBR-14, respectively. Cryopreservation of spermatozoa in 0.5-ml straws resulted in 22 and 20% plasma membrane- intact sperm cells, while spermatozoa frozen in 0.25-ml straws resulted in 34 and 31% PMI sperm cells for CMFDA and SYBR-14, respectively. No significant difference was observed (P > 0.05) for PMI spermatozoa stained with either CMFDA or SYBR-14. In addition, the ability to recover spermatozoa after freezing on the cryomicroscope establishes the Linkam BCS 196 as a useful tool for the study of sperm cell cryopreservation.

A novel human homologue of yeast nucleosome assembly protein, 65 kb centromeric to the p57KIP2 gene, is biallelically expressed in fetal and adult tissues

Three genes on 11p15.5 are known to undergo genomic imprinting. The gene for insulin-like growth factor II (IGF2) is normally expressed from the paternal allele, while H19 and p57KIP2, a cyclin-dependent kinase inhibitor, are expressed from the maternal allele. Five germline balanced chromosomal rearrangement breakpoints from patients with Beckwith-Wiedemann syndrome (BWS) have been mapped to 11p15.5 between p57KIP2 and IGF2, and all are derived from the maternal chromosome. By positional cloning from BWS breakpoints, we have isolated a gene 100 kb and 65 kb centromeric to the proximal end of this BWS breakpoint cluster and p57KIP2, respectively. This gene is homologous to yeast nucleosome assembly protein (NAP1) and to a human homologue of NAP1, and we designate it hNAP2 (human nucleosome assembly protein 2). hNAP2 diverges in its expression pattern from IGF2, H19, and p57KIP2, and it shows biallelic expression in all tissues tested. Thus, hNAP2 is functionally insulated from the imprinting domain of 11p15.

Development of a culture medium (BECM-3) for porcine embryos: effects of bovine serum albumin and fetal bovine serum on embryo development

Media are available that can deliver modest porcine embryonic development from a single-cell zygote to the blastocyst stage. However, few embryos develop to hatched blastocysts by Day 7 in vitro, indicating deficiencies in media that inhibit early embryonic development. A defined culture medium, Beltsville Embryo Culture Medium (BECM-3), was developed to support porcine zygote development to the blastocyst stage. When fetal bovine serum was added by late Day 5 (late morula/early blastocyst stage), 80% of total embryos cultured from Day 2 developed into hatched blastocysts by Day 8. There was also a significant increase in the mean cell number of blastocysts and hatched blastocysts when culture was performed in BECM-3-based media in the absence of BSA fraction V. These studies provide a chemically defined foundation for elucidating key developmental components of preimplantation pig embryos.

Comparison of detergent-solubilized membrane and soluble proteins from flow cytometrically sorted X- and Y-chromosome bearing porcine spermatozoa by high resolution 2-D electrophoresis

The only known and measurable difference between X- and Y-chromosome bearing spermatozoa is the small difference in their DNA content. The X sperm in the human carry 2.8% more DNA than the Y sperm, while in domestic livestock this difference ranges from 3.0 to 4.2%. The only successful sperm separation method, flow cytometric sorting, is based on this difference in DNA content. Using this technique, X and Y sperm populations with purities greater than 90% can be obtained. The number of spermatozoa that can be sorted in a given time period, however, is too low for application of this technique in routine artificial insemination. Therefore, the search for a marker other than DNA to differentiate between X and Y sperm remains of interest in order to develop a method for large scale X and Y sperm separation. The aim of the present study was to investigate whether porcine X and Y sperm contain some difference in their plasma membrane proteins. The flow cytometric sorting of sperm enabled a direct comparison of the proteins of the X and Y sperm populations. High resolution two-dimensional (2-D) electrophoresis was used; however, adaptations were needed to enable its use for analysis of proteins of flow cytometrically sorted sperm, both in the sorting procedure, membrane protein solubilization, and in the 2-D electrophoresis. Up to 1000 protein spots per gel could be detected and quantified. Comparison of the 2-D protein patterns revealed differences in protein spots between sperm of two individual boars. However, no differences in protein spots between the X and Y sperm fractions were found. These results provide additional support for the view that X- and Y-chromosome bearing spermatozoa are phenotypically identical, and cast doubt on the likelihood that a surface marker can provide a base for X and Y sperm separation.

Slit-scan flow cytometry for consistent high resolution DNA analysis of X- and Y-chromosome bearing sperm

This paper describes the application of slit-scan flow cytometry for accurate DNA analysis of X- and Y-chromosome bearing sperm. The introduction of the slit-scanning technique was initiated to improve the consistency in resolution of the X and Y population from donor to donor. An optimal resolution is essential for high purity sorting of X and Y sperm, as the difference in DNA content is small (3-4%) in most mammals. This difference is the discriminatory parameter for the flow cytometric sorting of the two populations. Our approach was to focus on the role of the sperm tail in the detection process. Slit-scan flow cytometric analysis allows the whole sperm to be spatially analyzed along the direction of flow. Sperm were stained with Dansyl Lysine, a UV excitable fluorescent membrane dye, which stained the head, midpiece, and principal piece. Analysis of these stained sperm showed that there was no difference between the relative number of sperm that travel headfirst or tailfirst through the detection zone of the flow cytometer. The influence of sperm with coiled tails on DNA analysis was also investigated. The proportion of sperm with coiled tails influences semen quality. The standard X-Y separation procedure uses Hoechst 33342, which stains all intact sperm, both living and dead. Propidium iodide was added to discriminate the dead sperm population. Slit-scan analysis showed that measurement of a sample containing a high proportion of living sperm with coiled tails results in an inferior DNA histogram and reduced X-Y resolution. Sperm with coiled tails can result in a lower detected fluorescence intensity, but the reason for this is unclear. Slit-scan flow cytometry allows exclusion of sperm with coiled tails from the analysis, resulting in a restoration of high resolution of X- and Y-chromosome bearing sperm populations.