Bovine sperm cells have a complement of 30 DNA chromosomes carrying the genes that determine the characteristics of the offspring. One of these chromosomes in each cell is the sex-determining chromosome, and is either the X chromosome, which determines that the offspring will be female, or the Y chromosome, which determines male offspring. Because the X chromosome is larger than the Y chromosome, there is a small difference in the total DNA between sperm cells one or the other. The difference is measured in order to determine which sperm cells are “male” or “female”.
The LumiSort™ instrument is a new technology based on flow cytometry (single cell analysis and sorting). It uses a safe and widely accepted method to determine the sex of sperm cells by staining the DNA of a semen sample with an innocuous dye that binds to DNA and emits fluorescent light when excited by a laser. Since female cells contain more DNA than male cells, the emitted fluorescence is slightly greater for female cells than male (by only about 3.7%); this difference is used to determine the sex of the cell.
Once the sex has been determined, LumiSort uses laser killing to delete the cells of the unwanted sex, leaving the desired cells untouched. In this way, the technology is extremely gentle on the desired cells, leaving them fully capable of fertilizing the egg. High fertility is a vital determinant of user acceptance and of reproductive efficiency.
LumiSort™ moves sperm cells in a fluid stream at high velocity past the laser based detection zone one cell at a time, analyzing each cell individually, to determine if the cell is “female” (bearing an X chromosome) or “male” (bearing a Y chromosome). LumiSort™ achieves this sex-determining step in a completely novel design that increases the rate at which male and female cells can be distinguished, while dramatically decreasing the wastage of cells that cannot be differentiated The instrument then functionally removes undesired (wrong-sex) cells from the preparation without subjecting the desired cells to harmful processes that are common to other flow cytometers, including high pressure differentials, rapid changes in velocity, and electrified fluid sorting that reduces the fertility of conventional sexed semen today. Additionally, since LumiSort™ determines the sex of every cell, resulting yields of cells of the desired sex are high, allowing for use on higher end sires, greatly expanding the range of semen available for sexing.
Comparison of LumiSort™ technology to the older technology.
The video below illustrates how LumiSort sperm sexing technology couples an innovative optical system for the detection of sperm cell sex, with laser killing of the cells that are not of the desired sex. Click to see a conception of the LumiSort instrument in operation.
The LumiSort instrument will achieve sperm cell sexing with unparalleled speed and efficiency by performing four basic operations. First, cells are positioned accurately and single file in a rapidly flowing fluid. The cells then pass into the analysis region of the instrument where they are illuminated with a light that causes them to glow brightly, taking advantage of a special fluorescent dye that permits the discrimination of female-determining sperm cells (slightly brighter) from male-determining cells (slightly dimmer). Next, the emitted light is collected by the LumiSort instrument’s sensitive light collection optics, taking advantage of 360-degree light collection to overcome a problem caused by the cells’ uneven light emission in different directions. With the sex determined, the fast electronics in the LumiSort instrument will control the delivery of lethal laser irradiation to a spot downstream of the analysis region, timed to coincide with the passage of sperm cells of the undesired sex. The cells of the desired sex pass through the instrument unharmed and are collected for processing, packaging, transportation and use in artificial insemination.