High pressure sperm sorting and flow cytometer methods
Cell sorting methods that improve sorting efficiency and productivity by elevating sorting pressures and incorporate certain steps to help the cells better survive such elevated pressures. In the case of sperm, sorting the steps of standardizing sperm samples, staining sperm samples in a single step, calibrating a flow cytometer to place sperm in the leading edge of droplets, and changing a catch fluid distance may be incorporated individually, or in combination to help sperm better survive the sex sorting process.
1. A method of sorting bovine sperm comprising:
extending a bovine sperm sample in an initial extender at a sperm sample to initial extender ratio between about 1:1 and 1:10 to form an extended bovine sperm sample;
reconcentrating the extended bovine sperm sample to a concentration between 900 million sperm per ml and 2400 million sperm per ml, wherein the reconcentrated sperm concentration is higher than the sperm concentration following dilution;
staining sperm in the reconcentrated bovine sperm sample with a DNA selective dye; and
sorting the stained sperm with a flow cytometer with a sheath fluid pressure between about 45 psi and about 65 psi, wherein the steps of extending and reconcentrating the bovine sperm sample reduces damage imposed on the sperm by the sheath fluid pressure.
2. The method of claim 1 , wherein the step of staining is performed with a modified TALP having the DNA selective dye and a quenching dye, a TES-TRIS having the DNA selective dye and a quenching dye, TRIS citrate having the DNA selective dye and a quenching dye, sodium citrate having the DNA selective dye and a quenching dye, or a HEPES based medium having the DNA selective dye and a quenching dye.
3. The method of claim 2 , wherein the modified TALP has a pH of between about 7.0 and about 7.8.
4. The method of claim 1 , wherein the stained bovine sperm sample is diluted in a staining media to a sperm concentration of: between 80 million sperm per ml and 160 million sperm per ml; between 160 million sperm per ml and 240 million sperm per ml; or between 240 million sperm per ml and 320 million sperm per ml.
5. The method of claim 1 , wherein the initial extender comprises one or more selected from the group consisting of: sodium bicarbonate, TRIS citrate, sodium citrate, HEPES, TRIS, TEST, MOPS, KMT, TALP, and combinations thereof.
6. The method of claim 5 , wherein the initial extender further comprises an antioxidant.
7. The method of claim 1 , further comprising the step of calibrating the flow cytometer.
8. The method of claim 7 , wherein the step of calibrating the flow cytometer further comprises producing a calibration side stream and providing each droplet in the calibration side stream which is expected to contain live sperm with a uniform trajectory.
9. The method of claim 7 , wherein the step of calibrating the flow cytometer further comprises adjusting instrument parameters so live sperm tend to be placed in a leading edge of forming droplets.
10. The method of claim 7 , wherein the step of calibrating the flow cytometer further comprises establishing a calibration side stream with the highest drop drive frequency at which there is no spraying.
11. The method of claim 1 , wherein the sheath fluid pressure comprises a pressure in a range: about 50 psi to about 55 psi; about 55 psi to about 60 psi; or about 60 psi to about 65 psi.
12. The method of claim 1 , wherein the steps of extending and reconcentrating the bovine sperm sample reduces the additional sperm damage imposed by pressures greater than 40 psi by about 50%, about 60%, about 70%, about 80%, about 90%, or by nearly 100%.
13. The method of claim 1 , wherein the step of sorting the stained sperm sample further comprises the step of sex sorting sperm into a viable X chromosome bearing population and/or a viable Y chromosome bearing population.
14. The method of claim 1 , wherein the sheath fluid pressure comprises a pressure between about 50 psi and about 60 psi, or at about 60 psi.