What Does a Tailless Transgenic Calf Tell Us?
The goal of a recent genetic engineering experiment was to see whether the
researchers could stop a lactating cow from producing one particular protein
in its milk. This protein (β-lactoglobulin, a whey protein) is not part of
human milk and has been suspected to be an allergen for infants who are
allergic to cow milk.
The experiment, from the perspective of the intended effect, succeeded. It
involved a complex procedure that used cell cultures, genetic engineering of
mice, and the subsequent cloning of genetically modified cow embryos.
Fifty-seven modified cow embryos were transferred to recipient cows, five
pregnancies ensued, and one calf was born. When lactation was hormonally
induced, the calf produced no β-lactoglobulin in its milk.
But the intended effect was not the only one. When the milk composition was
further investigated, the researchers found that, along with the repression of
β-lactoglobulin, the amount of a different whey protein was increased, and
there was a great increase in the amounts of casein proteins in the milk (α-
and β-casein each increased more than two-fold and κ-casein increased
four-fold). Overall the whey-to-casein ration shifted from 21:79 (in controls)
to 4:96 in the transgenic calf. This compensatory shift in proteins indicates,
in the words of the scientists, “an intricate balance of milk proteins
synthesis.” This balance was radically altered through the experiment. In
other words, while the experiment has the goal of causing a clearly demarcated
effect (no β-lactoglobulin production), it in fact alters the protein
composition of milk overall. Whether such global changes might imbue milk with
other unintended allergenic characteristics is unknown.
The researchers were astonished that, through the suppression of the whey
protein, the production of the casein proteins rose to a degree that is not
matched in experiments that target the over-production of casein proteins.
An additional and startling unintended effect of the experiment was that the
calf was born without a tail. Whether this was directly related to the genetic
manipulation itself was not clear. A mutation could have occurred in the
cell-culturing process, and genetically modified cloned embryos have, in other
experiments, developed into tailless calves.
Given the propensity of genetic engineers to do what seems doable, I wonder
who will pick up on this unintended effect and put it to use in the effort to
create tailless dairy cattle, since tails — from a utilitarian point of
view — get in the way during milking! We shouldn’t expect that any research
group tackling such a task will be concerned about how being tailless might
negatively impact a cow’s life. After all, so the thinking goes, someone will
come up with a new “solution” to address any unintended effects. It’s strange
how little thought is given to the fact that milk proteins do display an
“intricate balance,” and that tails are meaningful organs that have served
cattle for thousands of years. Maybe before we try to manipulate specific
characteristics — and end up changing the whole organism — we should learn
something about their significance within the life of the organism.
Jabed, Anower, Stefan Wagnera, Judi McCracken et al. 2012. “Targeted microRNA
Expression in Dairy Cattle Directs Production of β-lactoglobulin-free,
High-Casein Milk,” PNAS, doi/10.1073/pnas.1210057109. Available online: