As I’m sure most of you are aware, the human species isn’t really in immediate danger from dying out due to lack of mating partners (other reasons, I leave up to you). And after all, if all else fails, a trip to a sperm bank can often be arranged. But what about those rare animals growing steadily rarer from the encroachment of humans on their habitat? Well this is when you need to lend a hand. It’s time to preserve some…eland semen.
Nel-Themaat et al. “Isolation, culture and characterisation of somatic cells derived from semen and milk of endangered sheep and eland antelope” Reproduction, fertility, and development, 2007.
(An eland. A type of antelope found in Africa. Very large, for antelope anyway, they weigh a tonne! A real tonne! Like 2,200 kg.)
The eland as a species ain’t doin’ so good. It, along with many other species, is suffering encroachment from humans, whether from hunting, agriculture, or what have you, and the population is getting small and smaller. So humans have come in to lend a hand by cultivating some of these animals, breeding them to keep up the population. But this can be very hard as herds shrink and you begin to get smaller genetic pools, resulting in inbreeding problems. So how do you help maintain the diversity of your herd? Find yourself some wild semen and eggs. Of course, this can’t work if the candidate donors are dead. You need to keep the stocks of gametes (the eggs and sperm) pretty fresh in order for artificial insemination to work.
So instead, many people trying to increase populations of endangered species are turning to something called Somatic Cell Nuclear Transfer (SCNT). This is the method that brought us Dolly, and works by sucking out the nucleus of a normal somatic cell (meaning a body cell rather than a gamete like a sperm), and sticking it in the cell body of an ovum, which has had its nucleus removed. The nucleus of sperm and eggs are haploid, meaning they only have half their normal compliment of genetic material, while somatic cell nuclei are diploid (it occurs to Sci that she’s gonna have to explain meiosis some day…). Once the ovum has a full compliment of genes (which usually means that a sperm has joined up with it) it will begin to divide to produce a new animal.
But in the case of SCNT, the sperm never shows up. Instead, the ovum nucleus is replaced with a somatic cell nucleus which is diploid, having the full number of genes, and the cell is stimulated with an electric shock, to fool it that the right stuff has taken place. The ovum will then begin to divide, and if all goes well, you get Dolly, or your species of choice.
(TA DA!!! I have to say that I remember when Dolly was first cloned and how excited everyone was. It makes me feel really old that Dolly is now stuffed and living in a museum…)
The issue is now where to get the somatic cell. You can presumably use many different types, but a good source for somatic cells is freshly lactated milk or freshly ejaculated semen. Milk contain sTONS of somatic cells, which is a little gross to think of in terms of the baby, but so does semen. Semen is not just composed of sperm, there are lots of somatic cells along with it. So this paper set out to determine which was best, the milk or the semen, and how best to store it, using sheep milk, ram semen, and eland semen.
And of course, they didn’t just wanted to know if it worked, they wanted to know how best to store this stuff direct from the field. If you’re trying to preserve a wild animal species, and are trying to, say, transfer some genes from one reserve to another, you’re going to have to be able to take your animal down, get your goods, and get gone. But expensive cell culture ingredients are tough to carry around in the field, not to mention warm rooms and freezers. So the study also looked at what quick methods for preservation worked best: fresh, cooled, or frozen.
(Sheds a whole new light on these…)
In the case of milk, it was collected by the normal way, but how to collect semen from the ram and eland? For the rams, they used a technique pretty well known in the agricultural world: electroejaculation (which Sci might have to do another post on sometime, hehe). Sounds uncomfortable, but usually this is done under anesthesia. Place an electrode in the rectum right up against the prostate, and *ZAP*. The electric current stimulates the nerves nearby and produces ejaculation.
But apparently this wasn’t enough for the eland. He required both electroejaculation AND prostate massage via the rectum. Difficult to please, those eland.
They then kept the semen fresh, cooled it slowly, cooled it quickly, or flash froze it, and then tried to culture the somatic cells.
It turned out that flash freezing and quick cooling, which you would think would have produced the best results (due to stopping breakdown and metabolic processes quickly) actually produced the WORST results. In the case of the quick cooling, the cells divided once and then gave up the ghost, while flash frozen cells failed to divide at all. On the other hand, the fresh and slow cooled semen produced lovely layers of somatic cells in both the ram and the eland. This was the first time that anyone had tried to use the SOMATIC cells from semen, as opposed to just the sperm, and the cells appeared to form up pretty well.
As for the milk, the somatic cells appeared to reproduce just fine. But now the question was, could you perform SCNT? This had been done before in sheep, obviously, but what about the eland? There’s always a chance that the surrogate female will reject the resulting embryo, and another chance that eland somatic cells might not respond well to having their nuclei sucked out and replaced. But they did make it through the beginning stages, though neither of the female elands that were implanted managed a successful pregnancy. This is particularly difficult in eland and related species like cattle, where SCNT success rates are still below 4%, though this might be because conditions still need to be optimized.
So it appears that if you want to use your somatic cells, keep ‘em fresh or cooled, not frozen. Don’t want to spend too much time at the cold end of the gene pool.
Nel-Themaat, L., Gómez, M., Damiani, P., Wirtu, G., Dresser, B., Bondioli, K., Lyons, L., Pope, C., & Godke, R. (2007). Isolation, culture and characterisation of somatic cells derived from semen and milk of endangered sheep and eland antelope Reproduction, Fertility and Development, 19 (4) DOI: 10.1071/RD06153