Electrophoretic separation of X- and Y-chromosome-bearing sperm in human semen

Enrichment of bovine X-sperm using microfluidic dielectrophoretic chip: A proof-of- concept study

The microfluidic dielectrophoretic (MF-DEP) chip is a new, economical and readily-available technology that might be used to enrich X-sperm for increasing female offspring in dairy farms. In this study, we sought to develop an MF-DEP chip to enrich X bovine sperm. The MF-DEP chip was composed of an electrode attached to a glass slide and a microchannel made from polydimethylsiloxane. Sex-sorted sperm from flow cytometry were used to identify optimal electric field conditions while unsorted sperm were later tested for sorting efficiency. The results show that during dielectrophoresis some sperm attached to the electrode (called positive DEP; pDEP) whereas other moved away from the electrode (called negative DEP; nDEP). X and Y-sperm responded to dielectrophoresis differently depending on various factors such as buffers, voltages, and frequencies. We found that the condition 4 V 1 MHz significantly reduced (P < 0.05) the percentage of Y-sperm to nearly 30 and therefore enriched X-sperm. The sorting efficiency was dependent on buffer, bull, sorting cycle, flow rate, electrical voltage, and frequency. Notably, the best sorting buffer found in this experiment was the conducting buffer, but this buffer significantly reduced sperm viability and motility. Other sperm-friendly buffers, TRIS and mHTF, were also used, but could not enrich X-sperm. In conclusion, this is a proof of concept that the MF-DEP chip can be effectively used to enrich bovine X-sperm. However, more research must be performed particularly to find the best sorting buffer to effectively sex-sort sperm while providing high motility and sperm viability.

A FOLLOW-UP EXPANDED STUDY OF THE CORRELATION OF SPERM VELOCITY IN SEMINAL PLASMA AND OFFSPRING GENDER

A preliminary study reported finding higher sperm velocity in seminal plasma in males of partners that conceived female offsprings. The null hypothesis was that sperm velocity was not related to the offspring gender. The objectives were: (a) to expand the previous study, and (b) to correlate offspring gender results with motility parameters determined through the computer-aided sperm analyzer (CASA) system. In combined fresh and frozen cycles (N = 187), sperm from cases with all female offsprings displayed higher curvilinear (48 +/- 1.0 mu/sec versus male 46 +/- 1.0, P < 0.05) and average path velocities (36 +/- 0.7 mu/sec versus male 34 +/- 0.7, P < 0.01). A criteria of less than 30 mu/sec or over 41 mu/sec average path velocity predicted 73 or 72% of the male or female offspring cases, respectively. A curvilinear velocity of less than 49 mu/sec or over 55 mu/sec predicted 58 or 59 % of the male or female offspring cases, respectively. Semen viscosity reflected in sperm velocity was linked to predominantly male or female sperm populations. Paracrine signals from the gender-skewed sperm precursor populations controlling viscosity merit further exploration.

Sperm velocity in seminal plasma and the association with gender of offspring

The gender of the offspring is determined by the fertilizing sperm. Previous gender studies were based on washed sperm, but not on sperm in seminal plasma. The objective was to correlate motility parameters assessed during semen analyses with the offspring gender. For comparison, fixed sperm head DNA quantitated by Hoechst 33342 fluorescence microscopy was also analyzed. Forty-six patients undergoing assisted reproduction procedures resulted in livebirth deliveries with either male or female-predominant offsprings. Sperm head fluorescence was weakly correlated to the gender in 61% of the cases. Sperm of patients with male offsprings had slower curvilinear (44.2 +/- 1.8 mean +/- SEM, versus, 49.9 +/- 2.7 micro /sec) and slower average path velocities (32.4 +/- 1.2 versus 36.3 +/- 1.7 micro /sec). Using cut-off values for the curvilinear (< 49 micro /sec) and average path (< 36 micro /sec) velocities of sperm swimming in seminal plasma, the two parameters predicted 75 and 68% of the male offspring births, respectively. The data suggest that sperm movement in seminal plasma is a marker for factors that skew the ratio of the X- to Y-sperm populations.

Selection and separation of X- and Y- chromosome-bearing mammalian sperm

Preselection of the gender of offspring is a subject that has held man's attention since the beginning of recorded history. Most scientific hypotheses for producing the desired sex of offspring address separation of X- and Y-bearing sperm, and most have had limited, if any success. Eight of these hypotheses and their experimental verifications are discussed here. Three hypotheses are based on physical characteristics of sperm, one on supposed differences in size and shape, another on differences in density, and a third on differences in surface charge. There has been no experimental verification of differences based on size and shape, and the results from attempts to verify separation of X- and Y-bearing sperm based on density have been mixed. Electrophoresis may provide a method for separating X- and Y-bearing sperm, but it is currently unproven and would be of little practical utility, since sperm motility is lost. A fourth hypothesis employs H-Y antigen to select preimplantation embryos. This method reliably produces female offspring, but does not permit the selection of male offspring and does not work on sperm. There are two applications of the theory that X- and Y-bearing sperm should be separable by flow fractionation. Flow fractionation using thermal convection, counter-streaming sedimentation, and galvanization is highly promoted by its originator but has not gained wide acceptance due to lack of independent confirmation. Flow fractionation by laminar flow is said to provide up to 80% enrichment of both X- and Y-bearing sperm; however, this method also has not been confirmed by other workers or tested in breeding trials. The sixth theory discussed is that of separation through Sephadex gel filtration. This method may provide enrichment of X-bearing sperm, but, again, other experimenters have not been able to adequately confirm the enrichment. The best-known approach to sperm separation is that employing albumin centrifugation, yet even with this method, not all researchers have been able to confirm a final fraction rich in Y sperm, and trials in animals have given contradictory results. The most reliable method for separating X- and Y-bearing sperm is use of flow cytometric and flow sorting techniques. These techniques routinely separate fractions with a purity greater than 80% and can be above 90%. Unfortunately, these methods do not always work for human samples. Furthermore, as with electrophoretic approaches, the methods identify and separate only chemically fixed sperm and provide limited biological applications.(ABSTRACT TRUNCATED AT 400 WORDS)

Separation of human X and Y spermatozoa by free-flow electrophoresis

Free-flow electrophoresis is a fast and promising method for gamete separation. Pretreated seminal plasma-free human spermatozoa were injected continuously as a fine stream into the buffer medium of the separation chamber flowing perpendicular to the forces of an electrical field, which separated the spermatozoa according to their differences in electrophoretic mobility. For characterization of the two classes of spermatozoa before and after separation, quinacrine mustard staining was used to identify the Y-chromosome-bearing spermatozoa carrying the fluorescent body (F-body). Human spermatozoa moved toward the anode and were separated into two main peaks. The faster moving fraction contained nearly 80% Y-bearing spermatozoa and the slower peak consisted mainly of pure X-bearing spermatozoa. Whereas sperm viability as determined by eosin staining was nearly unchanged, sperm motility was reduced after free-flow electrophoresis.