A cognitive task analysis for dental hygiene

To be an effective assessment tool, a simulation-based examination must be able to evoke and interpret observable evidence about targeted knowledge, strategies, and skills in a manner that is logical and defensible. Dental Interactive Simulations Corporation's first assessment effort is the development of a scoring algorithm for a simulation-based dental hygiene initial licensure examination. The first phase in developing a scoring system is the completion of a cognitive task analysis (CTA) of the dental hygiene domain. In the first step of the CTA, a specifications map was generated to provide a framework of the tasks and knowledge that are important to the practice of dental hygiene. Using this framework, broad classes of behaviors that would tend to distinguish along the dental hygiene expert-novice continuum were identified. Nine paper-based cases were then designed with the expectation that the solutions of expert, competent, and novice dental hygienists would differ. Interviews were conducted with thirty-one dental hygiene students/practitioners to capture solutions to the paper-based cases. Transcripts of the interviews were analyzed to identify performance features that distinguish among the interviewees on the basis of their expertise. These features were more detailed and empirically grounded than the originating broad classes and better serve to ground the design of a scoring system. The resulting performance features were collapsed into nine major categories: 1) gathering and using information, 2) formulating problems and investigating hypotheses, 3) communication and language, 4) scripting behavior, 5) ethics, 6) patient assessment, 7) treatment planning, 8) treatment, and 9) evaluation. The results of the CTA provide critical information for defining the necessary elements of a simulation-based dental hygiene examination.

Birth of piglets after transfer of embryos cryopreserved by cytoskeletal stabilization and vitrification

Pig embryos suffer severe sensitivity to hypothermic conditions, which limits their ability to withstand conventional cryopreservation. Research has focused on high lipid content of pig embryos and its role in hypothermic sensitivity, while little research has been conducted on structural damage. Documenting cytoskeletal disruption provides information on embryonic sensitivity and cellular response to cryopreservation. The objectives of this study were to document microfilament (MF) alterations during swine embryo vitrification, to utilize an MF inhibitor during cryopreservation to stabilize MF, and to determine the developmental competence of cytoskeletal-stabilized and vitrified pig embryos. Vitrified morulae/early blastocysts displayed MF disruptions and lacked developmental competence after cryopreservation; hatched blastocysts displayed variable MF disruption and developmental competence. Cytochalasin-b did not improve morula/early blastocyst viability after vitrification; however, it significantly (P < 0.05) improved survival and development of expanded and hatched blastocysts. After embryo transfer, we achieved pregnancy rates of almost 60%, and litter sizes improved from 5 to 7.25 piglets per litter. This study shows that the pig embryo cytoskeleton can be affected by vitrification and that MF depolymerization prior to vitrification improves blastocyst developmental competence after cryopreservation. After transfer, vitrified embryos can produce live, healthy piglets that grow normally and when mature are of excellent fecundity.

Low dose insemination in synchronized gilts

Conventional insemination techniques in pigs require 2 to 3 x 10(9) sperm/dose. When using the latest high-speed sperm-sorting technology, one can still sort only about 5 to 6 million sperm of each sex per hour. The objective of the present study was to find the minimal sperm concentration at a low-insemination volume in pigs without diminishing fertilization rate and litter size using surgical deep intra-uterine insemination (IUI). Semen from 3 boars was collected and diluted with Androhep to 5 x 10(8), 1 x 10(8), 1 x 10(7), 5 x 10(6) or 1 x 10(6) sperm/0.5 ml. In trial 1, 109 prepuberal gilts were synchronized and surgically inseminated into the tip of each uterine horn 32 h or 38 h after hCG treatment or at the time of ovulation, respectively. Pregnant gilts were allowed to go to term. Pregnancy and farrowing rates did not differ significantly except at the lowest sperm concentration if inseminated 32 h or 38 h after hCG treatment (p < 0.05). No differences were found among insemination groups for the total number of piglets, number of piglets born alive, stillborn piglets, and mummified fetuses. In trial 2, 34 gilts were inseminated as described above 32 h after hCG. Additionally, 9 gilts were inseminated once nonsurgically with 1 x 10(9) sperm as controls. Gilts were slaughtered 48 h after insemination, and embryos were recovered. Embryos were cultured in NCSU 23 (120 h), evaluated morphologically and stained with fluorescent dye (Hoechst 33342) to visualize nuclei. Recovery rates varied between 71.4% and 84.4%. Fertilization rate of the lowest sperm concentration (1 x 10(6) sperm/horn) differed significantly (p < 0.05) from all other groups. Cleavage rates at specific developmental stages did not differ. After 5 days of in vitro culture, embryos developed to morulae and blastocysts. No differences were found for these stages. In conclusion, no major differences were found between insemination groups as long as the sperm dosage was at least 10 million sperm per gilt. The low volume was sufficient for successful deep intra-uterine insemination. Embryo development was comparable to the controls.

Sex preselection: laboratory validation of the sperm sex ratio of flow sorted X- and Y-sperm by sort reanalysis for DNA

Laboratory validation is essential in developing an effective method for separating X and Y sperm to preselect sex. Utilizing sexed sperm from a particular experiment to test fertility and achieve the subsequent phenotypic sex without knowing the likely outcome at conception is too costly for most applications. Further, research advances need to be built on an ongoing assessment with respect to the collection of data to continue progress towards achieving a successful outcome. The Beltsville Sperm Sexing Technology, which is based on the sorting of X- and Y-bearing sperm through the process of flow-cytometric sperm sorting, is also well suited for validation in the laboratory by "sort reanalysis" of the sperm X- and Y-bearing fractions for DNA content. Since the sexing technology is based on the use of Hoechst 33342, a permeant nuclear DNA stain for sorting X- and Y-bearing sperm, it also can be the marker for determining the proportions of X and Y populations by sort reanalysis. The process consists of using an aliquot of the sorted sperm and sonicating to obtain sperm nuclei. The uniformity of the nuclear staining is re-established through the addition of more Hoechst 33342. Separate analysis of each aliquot produces a histogram that is fitted to a double gaussian curve to determine proportions of X and Y populations. The relative breadths of the distributions of DNA of X- and Y-bearing sperm within a species affects interpretations of the histogram. Sort reanalysis is consistently repeatable with differences in X/Y DNA equal to or greater than 3.0%. This information on sex ratio of the sperm then provides the precise tool by which one can predict the outcome in terms of sex, from a particular sample of semen. Simple analysis of unsorted sperm to determine the proportions of X- and Y-bearing sperm based on DNA content is also an effective tool for validating sperm-sex ratio, whether it is in a sample assumed to be 50:50 or predicted to be something other than 50:50. This simple analysis provides for a check on the potential sex ratio of any sample of semen.

Physiology of spermatozoa at high dilution rates: the influence of seminal plasma

Extensive dilution of spermatozoa, as occurs during flow-cytometric sperm sorting, can reduce their motility and viability. These effects may be minimized by the use of appropriate dilution and collection media, containing balanced salts, energy sources, egg yolk and some protein. Dilution and flow-cytometric sorting of spermatozoa, which involves the removal of seminal plasma, also destabilizes sperm membranes leading to functional capacitation. This membrane destabilization renders the spermatozoa immediately capable of fertilization in vitro, or in vivo after deposition close to the site of fertilization, but shortens their lifespan, resulting in premature death if the cells are deposited in the female tract distant from the site of fertilization or are held in vitro at standard storage temperatures. This functional capacitation can be reversed in boar spermatozoa by inclusion of seminal plasma in the medium used to collect the cells from the cell sorter and, consequently, reduces their in vitro fertility. It has yet to be determined whether seminal plasma would have similar effects on flow cytometrically sorted spermatozoa of other species, and what its effects might be on the in vivo fertility of flow sorted boar.

Sex preselection: high-speed flow cytometric sorting of X and Y sperm for maximum efficiency

Sex preselection that is based on flow-cytometric measurement of sperm DNA content to enable sorting of X- from Y-chromosome-bearing sperm has proven reproducible at various locations and with many species at greater than 90% purity. Offspring of the predetermined sex in both domestic animals and human beings have been born using this technology since its introduction in 1989. The method involves treating sperm with the fluorescent dye, Hoechst 33342, which binds to the DNA and then sorting them into X- and Y-bearing-sperm populations with a flow cytometer/cell sorter modified specifically for sperm. Sexed sperm are then used with differing semen delivery routes such as intra-uterine, intra-tubal, artificial insemination (deep-uterine and cervical), in vitro fertilization and embryo transfer, and intra-cytoplasmic sperm injection (ICSI). Offspring produced at all locations using the technology have been morphologically normal and reproductively capable in succeeding generations. With the advent of high-speed cell sorting technology and improved efficiency of sorting by a new sperm orienting nozzle, the efficiency of sexed sperm production is significantly enhanced. This paper describes development of the these technological improvements in the Beltsville Sexing Technology that has brought sexed sperm to a new level of application. Under typical conditions the high-speed sperm sorter with the orienting nozzle (HiSON) results in purities of 90% of X- and Y-bearing sperm at 6 million sperm per h for each population. Taken to its highest performance level, the HiSON has produced X-bearing-sperm populations at 85 to 90% purity in the production of up to 11 million X-bearing-sperm per h of sorting. In addition if one accepts a lower purity (75 to 80%) of X, nearly 20 million sperm can be sorted per h. The latter represents a 30 to 60-fold improvement over the 1989 sorting technology using rabbit sperm. It is anticipated that with instrument refinements the production capacity can be improved even further. The application of the current technology has led to much wider potential for practical usage through conventional and deep-uterine artificial insemination of many species, especially cattle. It also opens the possibility of utilizing sexed sperm for artificial insemination in swine once low-sperm-dose methods are perfected. Sexed sperm on demand has become a reality through the development of the HiSON system.

In vitro production of sexed embryos for gender preselection: high-speed sorting of X-chromosome-bearing sperm to produce pigs after embryo transfer

The objectives for the present experiments were to apply sperm sexing technology to an in vitro production system with porcine oocytes obtained from slaughterhouse material. On six experimental days, ovaries were obtained from an abattoir, and cumulus-oocyte-complexes were matured in vitro. Semen was collected from mature boars of proven fertility and was sorted for X-chromosome-bearing sperm, using the Beltsville Sperm Sexing Technology incorporating the use of high-speed sorting. A total of 5,378 oocytes were submitted for in vitro fertilization (IVF). Of these, 559 ova were stained for cytogenetic analysis 18 h after IVF. From the remaining 4,819 ova, 1,595 cleaved, and 1,300 of the cleaved embryos were transferred into 26 synchronized recipients (5 control gilts for unsorted sperm, 21 gilts for X-sorted sperm). In a test of two fertilization media (FERT-A vs FERT-B) higher cleavage rates (P<.05) were obtained when FERT-B was used as a fertilization medium for unsorted (43.4+/-5.1%) and sorted sperm (43.1+/-1.1%;), whereas in FERT-A unsorted sperm gave a cleavage rate of 17.9+/-4.4% and sorted sperm gave 30.4+/-1.4%. Additionally, cleavage rates were higher (P<.05) after fertilization with sorted sperm vs unsorted sperm, independent of fertilization medium. Cytogenetic analysis of ova revealed that more oocytes with unsorted than with sorted sperm remained in Metaphase 2 arrest (P<.05). This was also independent of the fertilization medium. Monospermic fertilization rates were the same for IVF with unsorted or sorted sperm, independent of the fertilization system, except FERT-A with unsorted sperm (P<.05). Polyspermic fertilization rates were highest in FERT-B (37.6+/-6.6). A total of 57 pigs were born from nine litters. Six litters from sexed sperm (X-sorted) produced 33 females (97%) and one male. Three litters from control transfers produced 23 pigs, 11 of which were female (48%). The sex ratio of the offspring was predicted based on the sort reanalysis of the sorted sperm for DNA content.

Development of standards for the design of educational software. Standards Committee for Dental Informatics

The ready availability of computers, combined with the advent of sophisticated software development tools, has resulted in a proliferation of dental instructional software. The quality of these products varies widely. Working Group 5 of the Standards Committee for Dental Informatics has published an initial set of guidelines to help course designers develop high-quality instructional materials. In the future, these guidelines will evolve into standards. This article summarizes the guidelines and considers future actions that may be taken once the standards are in place.

Instructional characteristics of online continuing education courses

OBJECTIVE

The purpose of this study was to determine the instructional characteristics of online continuing dental education courses on the World Wide Web.

METHOD AND MATERIALS

One hundred fifty-seven online courses offered by 32 providers were reviewed for 34 criteria.

RESULTS

Courses of various types spanned a variety of topics. Approximately half of all courses offered continuing dental education credit. The relationship between credit hours and course length was quite variable. Most courses consisted of text and images. Very few courses used advanced media such as video clips. Measured against an index of instructional quality developed for this study, the instructional quality of the courses, in general, was poor. Most for-credit courses contained self-assessment questions, but only 28% of courses scored the questions online. Basic information that was missing on many courses included the authors' names (29%); the intended audience (81%); goals and objectives (77%); and references (85%). In 47% of the courses, there was no opportunity to provide feedback to either the author or the provider.

CONCLUSION

The theoretical advantages of Web-based continuing dental education are numerous, but the currently available online resources are mostly of unacceptable quality.

The Internet--approaching a ubiquitous tool for dental education

The Internet holds promise of addressing some of dentists' and dental students' needs caused by the rapid expansion of knowledge. The Internet is used primarily for communication and for courses, but the quality of Internet courses is uneven. The Internet holds potential in formal dental education for supporting information and instructional databases and as an educational administrative tool. The use of the Internet for educational purposes raises issues such as locating resources on line, ensuring information quality, and incorporation of emerging computer architecture. Some projections are offered for the future: increased instructional quality, replacement of textbooks, creating "courses" out of modules of instructional material, faculty becoming coaches, increased use of trained instructional technologists, intelligent tutoring systems, and the merging of information, instruction, and practice systems. Numerous web sites are given.

The relationship between membrane status and fertility of boar spermatozoa after flow cytometric sorting in the presence or absence of seminal plasma

The motility, viability (percent live), capacitation status and in vitro fertility of boar spermatozoa were examined, after staining with Hoechst 33,342 and flow cytometric sorting in the absence or presence of seminal plasma. Viability was higher in unstained controls and when seminal plasma was present in the medium used to collect spermatozoa from the cell sorter than when seminal plasma was absent or in the staining extender only, but motility was highest when seminal plasma was included in the extender only, compared with the controls and other treatments. The proportions of capacitated spermatozoa were increased by sorting, but were lower when seminal plasma was present, rather than absent, from the staining extender and the collection medium. Compared with unstained controls, extension and staining without sorting only increased the proportion of capacitated spermatozoa after washing in preparation for in vitro fertilization. The percentages of polyspermic, penetrated and cleaved oocytes were lower when inseminated with unsorted (stained) than control (unstained) spermatozoa, regardless of the presence or absence of seminal plasma. These parameters were higher for sorted than for control spermatozoa in the absence of seminal plasma, but in its presence penetration and cleavage were substantially lower. The proportions of capacitated spermatozoa were lower when seminal plasma was present in the collection medium only than in the staining extender or when it was absent altogether, but the former treatment substantially reduced the proportions of polyspermic, penetrated and cleaved oocytes, and the proportion of blastocysts. These findings indicate that sperm capacitation associated with flow cytometric sorting can be reduced by the inclusion of seminal plasma in the collection medium, but this treatment reduces the ability of spermatozoa to fertilize oocytes in vitro under these conditions.

Sexual dimorphism in IVM-IVF bovine embryos produced from X and Y chromosome-bearing spermatozoa sorted by high speed flow cytometry

The objective of this study was to examine preimplantation development and sperm aster characteristics of bovine male and female embryos produced by using spermatozoa sorted for the X or Y chromosome. In vitro matured oocytes were inseminated at 24 h of maturation with sorted X or Y chromosome-bearing spermatozoa, using either fresh or frozen-thawed semen. Samples were taken from each sperm group 12 h post insemination (hpi), fixed, and immunostained for the microtubule cytoskeleton. Confocal microscopy enabled visualization of sperm aster formation and microtubule characteristics of each zygote during early fertilization. Cultured embryos were checked for cleavage at 30, 35, 40 and 45 hpi, embryo development was examined daily until Day 8 of culture. Blastocyst cell numbers were determined at the end of the experiments. Reanalysis of the sorted sperm cells for DNA content showed purity rates of 90.1 and 92.1% for X and Y chromosome-bearing spermatozoa, respectively. Reduced fertilization and development rates were observed when sorted spermatozoa were used compared with fresh and frozen-thawed spermatozoa. Penetration rates at 12 hpi were 39.5, 44.7, 55.9 and 79.0%, while blastocyst formation rates at Day 8 were 26.7, 26.5, 31.7 and 40.7% for X and Y chromosome-bearing spermatozoa, using fresh and frozen-thawed semen groups, respectively. Sperm aster size was larger in males than females, while the size of pronuclei and subjective grade of sperm aster quality showed no differences between sexes. In this study, a greater cleavage rate and sperm aster size in male embryos indicated a dimorphic pattern of development in male and female embryos during fertilization and first cleavage.

In vitro production of pig embryos: comparisons of culture media and boars

The utilization of in vitro produced pig embryos for commercial production or research is dependent upon the development of improved methodology. Our objective was to establish a consistent in vitro embryo production (IVP) system and subsequently utilize the procedures to evaluate culture system components and boar effects. To summarize the IVP system, 403 inseminated oocytes from a total of 2243 were analyzed across 17 replicates for maturation and fertilization efficiency, while 1838 zygotes were cultured in 26 replicates for developmental data. Penetration, cleavage and blastocyst development rates were determined at 18, 44 and either 144 or 168 h post insemination, respectively. Monospermic penetration averaged 31.8+/-7.3% while polyspermy was 30.8+/-17.2%. Cleavage rate was 44.9+/-16.1%, with 21.8+/-7.5% of fertilized oocytes and 51.9+/-15.9% of cleaved embryos developing to blastocysts. For culture medium comparison, fertilized oocytes were cultured in either BECM-6, BECM-7, NCSU-23 or NCSU-23aa and supplemented on Day 5 post insemination (pi) with 10% FCS. These treatments resulted in 4.0, 4.9, 19.8 and 13.6% (+/-3.2%) blastocysts by Day 7 pi, with an average cell number of 44.4+/-9.0, 65.1+/-8.2, 61.3+/-4.5 and 64.4+/-4.8, respectively. These IVP procedures consistently produced zygotes from semen of several different boars, capable of forming blastocysts in vitro. Comparison of developmental rates among the boars indicated that this system is variable among boars but not strictly boar-dependent. Culture media comparisons suggest that NCSU-23 yielded a higher percentage of blastocysts than the other media in this IVP system.

A novel nozzle for more efficient sperm orientation to improve sorting efficiency of X and Y chromosome-bearing sperm

Efficient high-resolution detection of DNA for flow cytometric sorting of X and Y chromosome-bearing sperm is dependent on effectively orientating the sperm head to the laser beam in orthogonally configured flow systems. Normally, a beveled needle is required to enlarge the fraction of properly orientated sperm (flat side facing the laser beam). In this report, a modification to a standard jet-in-air nozzle for improved sperm orientation is presented. Inside the modified nozzle (novel nozzle), orientation forces are applied lower in the nozzle than in the current beveled injection needle system. The nozzle was tested with sperm heads from several species. This study shows that use of the nozzle to orientate cattle, swine, rabbit, mouse, and human sperm effectively improves the percentage of sperm that are properly oriented. The percentage of sperm heads oriented by use of the former system (beveled needle) ranges around 30% for most species. With the newly designed nozzle, that percentage ranges around 60%. At least a twofold increase in analysis is achieved. It was found that, unlike results with the beveled needle, the percentage of properly oriented sperm was independent of the sample rate. The introduced nozzle is a significant improvement over the beveled needle system for the analysis and sorting of sperm on the basis of DNA content. In addition to the improvement in sorted sperm production brought about by the novel nozzle when fitted to standard-speed cell sorters, it clearly also has significant potential for improving the efficiency of the Beltsville Sperm Sexing Technology for separating X and Y chromosome-bearing sperm when adapted to high-speed cell-sorting systems.

Birth of piglets preselected for gender following in vitro fertilization of in vitro matured pig oocytes by X and Y chromosome bearing spermatozoa sorted by high speed flow cytometry

The present study examined the ability to establish pregnancies after transfer of pig embryos derived from in vitro fertilization (IVF) of in vitro matured (IVM) oocytes by X and Y chromosome-bearing spermatozoa sorted by flow cytometry. Cumulus-oocyte complexes (COC) were cultured in BSA-free NCSU-23 medium containing porcine follicular fluid (10%), cysteine (0.1 mg/mL), epidermal growth factor (10 ng/mL), LH (0.5 microgram/mL) and FSH (0.5 microgram/mL) for 22 h, then the oocytes were cultured without hormonal supplements for an additional 22 h. Boar semen was collected and prepared by flow cytometry sorting of X and Y chromosome bearing spermatozoa. After IVM, cumulus-free oocytes were co-incubated with sorted X or Y spermatozoa (2 x 10(4)/mL) for 6 to 7 h in modified Tris-buffered medium containing 2.5 mM caffeine and 0.4% BSA. After IVF, putative embryos were transferred to NCSU-23 medium containing 0.4% BSA for culture. A portion of the oocytes was fixed 12 h after IVF, the remainder were cultured up to 96 h. At 96 h after IVF, 8-cell to morula stage embryos (n = 30 to 35) from each gender were surgically transferred to the uterus of recipient gilts. Insemination of IVM pig oocytes with X- or Y-bearing sperm cells did not influence the rate of penetration (67 vs 80%), polyspermy (40 vs 53%), male pronuclear formation (95 vs 96%), or mean number of spermatozoa per oocyte (1.6 vs 1.6), respectively. Furthermore, no difference was observed between cleavage rates at 48 h after IVF (X, 49 vs Y, 45%). Transfer of embryos derived from X-bearing spermatozoa to 18 recipients resulted in 5 pregnancies and delivery of 23 females and 1 male piglet. Similarly, transfer of embryos derived from Y-bearing sperm cells to 10 recipients resulted in 3 pregnancies, with 9 male piglets delivered. The results show that X- and Y-bearing spermatozoa sorted using USDA sperm sexing technology can be successfully used in an IVM-IVF system to obtain piglets of a predetermined sex.

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.