From Leonberg to LPN1—A Genetics Perspective With a Stop Off at

From Leonberg to LPN1—A Genetics Perspective
With a Stop Off at Tyras’ Toy Factory
Trial, Error, and Art
One hundred and seven years before James D. Watson and Francis
Crick built their model of DNA, Heinrich Essig was busy breeding the
first litter of Leonberger puppies. This was 1846. It would be thirteen
years before Darwin’s Origin of the Species would be published
describing the processes underlying natural and artificial selection.
And, although Gregor Mendel was breeding pea plants at the same
time that Essig was breeding Leonbergers, it would be another fifty-four
years before his revolutionary work would come to light giving birth to
the science we know as genetics.
So, what Essig did, he did
through trial, error and art. He, like
all the other dog breeders who were
busily creating the hundreds of
breeds we know today, was
mastering the practicalities of
manipulating
genes
without
knowing it.
Based on what was visible to
him, he chose and mixed ingredients somewhat in the manner of a
good cook. He bred a pair of dogs, observed the results, tried a new
combination, got closer to his vision, and kept breeding until he could
predict fairly well how a litter of puppies would look and how they
would behave.
Most of the time he got what he wanted. And he wanted big,
elegant, light colored, friendly, healthy, longhaired dogs. Sometimes
though, he got grey dogs, sometimes spotted, sometimes gold, some
with, and some without masks. Mostly they were smart and healthy.
But sometimes they, like Para, one of the first pair he sent on the fortyday ocean voyage to America in 1879, got sick and died. Being an
outstandingly responsible and generous businessman, he immediately
sent a replacement.
After Essig’s death, Leonberger breeders continued to use the tried
and true methods of observing, analyzing, and then making
adjustments in the choices of mates.
They focused on those structural and
character traits that most differentiated
Leonbergers from their Saint Bernard
cousins with whom they were often
compared. Refined heads with gently
sloping stops became very important
traits. Since the first standard had
finally been written in 1895, most
of them were using the same
“recipe.” They got better at
breeding dogs that looked and
behaved in a predictable way.
They were mating wolf-gray, lionyellow, or red-gold dogs with
smooth
topcoats
and
rich
undercoats. They aimed for
structurally balanced dogs that moved well in a calm but still lively
manner. Most of the time it worked, but there were always surprises
along the way.
By the end of World War I, when the breed had to be reconstructed,
breeders in Leonberg did not have to start from scratch. They were able
to find surviving dogs that possessed standard Leonberger traits.
Although they may have heard rumors about the significance of newly
minted concepts and terms such as gene and genetic mutation, they
couldn’t relate the new ideas to their practices. The new science of
genetics was still confined to the halls of universities.
Throughout the next 50-60 years, in Germany and most of the
surrounding European countries Leonberger breeders kept getting better
and better at turning out beautiful, well-tempered and for the most part
healthy Leonbergers that looked and acted as predicted. Leonbergers
got more “typey” in spite of the upheaval caused by another World
War that totally disrupted their lives and litters.
Enter Mendelian Genetics
In the post-war period, both science and dog breeding flourished.
Scientists began explaining Mendelian genetics to the world outside of
the classroom. Geneticists gave breeders of horses, cows, chickens,
corn, wheat, lilies and Leonbergers a whole set of new tools to work
with. Breeders became acquainted with the primary tenets relating to
the transmission of hereditary characteristics from parent organisms to
their offspring. Science had provided ways to tie the causative effects of
invisible genes to the highly visible traits that were the object of their
efforts. Books providing detailed explanations of canine traits based on
Mendelian principles began popping up in the libraries of serious
breeders. Breeders learned to observe traits and determine if the
associated genes were dominant or recessive, sex-linked or not,
expressed all of the time or only some of the time. In addition, they
learned that some desirable traits brought not so desirable traits along
with them.
That is how disease-causing mutations slipped in to the Leonberger
genome. Some lay hidden for a while and then popped up as
unpleasant and tragic surprises. Several hereditary diseases now plague
our dogs. Some are deadly like osteosarcoma and hemangiosarcoma.
Some like LPN vary in severity and age of onset. Others, like thyroid
disease, can be controlled by drugs. Many orthopedic disorders can
sometimes be addressed with surgically or mechanical devices. But,
regardless of their severity, all diseases and disorders lead to a certain
amount of heartbreak.
Leonberger breeders can be proud of how well they have kept pace,
and often taken the lead, when it came to applying classical Mendelian
principles in attempts to limit genetic disease in our breed. But, with
20,000 genes to consider, classical genetics alone cannot give breeders
the power to predict just which genes (or their variants) will segregate
and how they might assort themselves in any given breeding.
The DNA Revolution
Breeders in America brought the Leonberger into the DNA
revolution very early when Addison’s Disease appeared unexpectedly.
Mary Decher and Waltraut Zieher set a standard for all breeders when
they chose to address the problem straight on through education and
direct contact with scientists. Carol Lewis, who owned one of the
affected dogs, says she still gets goose bumps when she recalls the
moment that Professor Ry Wagner isolated her dogs DNA. Mary,
Waltraut and Carol stood in awe of the potential demonstrated by that
fuzzy, white molecule. Residing on that molecule was a key that that
could be used to prevent the spread of the disorder in the breed. As it
turned out, principles of classical breeding coupled with courageous,
immediate action solved the problem.
Within the same time period, Judy Johnston and Ann Rogers began
to observe a strange complex of symptoms in their dogs. They followed
the example set by Mary and Waltraut. They spoke up, located helpful
scientists and began a fifteen-year quest that resulted this spring in the
triumphant announcement that at least one of the genes responsible for
the disorder known now as Leonberger Polyneuropathy had been
identified. Breeders all over the world now have the power to identify
the presence of the LPN1 mutation if it exists in their dogs.
There is much to learn about courage and determination from these
two sets of women. They formed the initial partnerships with molecular
biologists and geneticists who are working to minimize the impact of
genetic diseases in dogs. Scientists are not only providing genetic tests
to assist breeders, they are helping us change the way we think about
the power and complexity of artificial selection processes.
Now, when we think about genes, we don’t just observe our dog’s
appearance and behavior, we start to think about the specific
molecular action taking place. We now know that each functioning
gene is actually DNA code that results in the formation of proteins.
These proteins combine biochemically with other atoms and molecules
to form the trillions of molecular machines that build and maintain our
dog’s bodies. Genetic mutations alter the proteins formed and it is these
molecular changes that determine or alter our dog’s physical attributes
and health. When a gene and its processes can be identified, it can
come under our control given the right knowledge and tools. If we
learn through genetic analysis that a trait, even if it is a disease trait, is
inherited it’s good news. Science is giving us the power to choose
whether or not we want that trait in our breed. And, science is
providing us with new high-powered precision tools to act on our
choices. As with any new set of complex precision tools, we have to
learn how best to use them.
We All Need Tools to Learn to Use the Tools
One of the best tools I’ve found so far to start to get a handle on the
complexity of molecular genetics is a metaphor designed by Professor
Betsey Dextor Dyer for her Wheaton College course on the Basics of
Genetics. It’s a tool that has helped me to visualize and keep track of
the large number of items, relationships, and some of the more
complex genetic processes that go beyond the simpler Mendelian ones.
Because we can all easily picture an assembly line of machines, a
factory metaphor gives us some
built-in reference points when we try
to understand the trillions of
unimaginatively
tiny
molecular
machines
that
are
designed,
controlled,
and
maintained
according to DNA blueprints.
Dr. Dyer uses a cookie factory as
her model. To make the metaphor a
bit more relevant to Leo folks, I’ve
changed the metaphor to a toy
factory. My imaginary output is a based on a real toy Leonberger that
was manufactured at the end of the nineteenth century, by the
Lehmann Toy factory in Germany. Their wonderful walking tin
Leonberger was named Tyras.
Imagine an assembly line that the Lehmanns might have set up to
manufacture lots of
Tyrases according to
his blueprint. It takes
ten machines to make
and
package
our
Tyras
toys.
Each
machine has been
made from its own set
of blueprints and
comes with specific operating instructions. Our imaginary assembly
line is arranged in the following order:
1. A metal stamping machine that makes the body parts.
2. The first fork in the path: A two-part paint machine that colors
some parts to make lion-yellow Tyrases and the rest to make
reddish-gold Tyrases.
3. A body parts assembly machine.
4. A screw tightening machine.
5. A motor insertion machine.
6. A second fork in the path: A sorting machine designed to
remove broken parts or bent Tyrases.
7. A third fork in the path: A collar supplying machine that
provides fancy collars to one-third of the Tyrases.
8. A counting machine which sets out the right number of
Tyrases for shipping to stores.
9. A packaging machine.
10. A labeling machine.
Now, Professor Dyer suggests that we put the whole assembly line
into a black box so we can’t see what is going on inside. We can only
look at the output. We wait and watch for some little mistake to be
made and we record what happens to the toy dogs. This approximates
what our breeders have had to do for 160 years and what geneticists
are doing now when they are searching for a mutation causing a
disease.
According to Professor Dyer, here is how you would analyze the
Tyras output if you were trying to decipher what was happening as a
geneticist would:
Some mistakes (mutations to the instructions for the
machines) seem trivial and have little effect on the
important aspect of the Tyras toy, like how much fun he is
to play with. For example:
• The labeling machine spells Leonberger wrong.
• There are thirteen toys in the packing box instead of a
dozen.
Other mistakes seem to cause a complete absence of an
expected Tyras (but we do get a “default” Tyras). For
example:
• There are no red-gold Tyrases at all, only lion-yellow
ones.
• There are no toy dogs with collars
Still other mistakes have dramatic effects. For example:
• The toy dogs aren’t assembled and therefore cannot
be sorted by the sorting machine, cannot get collars,
cannot be counted, cannot be packaged. Only
horribly deformed and mangled parts come out of the
factory.
• No toy dogs emerge at all. Could there be something
wrong with the metal stamping machine? Perhaps no
tin sheets were inserted.
Things to notice:
• The hierarchy of seriousness of the mutations has
something to do with the order of events. Certain
early-acting machines can have a cascading effect on
the subsequent machines. Some early-acting
machines can even prevent the entire pathway from
functioning.
• At the places where paths fork, we can have mutations
that eliminate one possibility but not the other (collars
versus no collars).
• Events at the end of this pathway seem to be less
important to the overall product.
This is what geneticists think about—metaphorically—when they
are using the results of mutations to try to understand and reconstruct
the order of events of a hidden cell pathway. In addition to watching
for single mistakes (mutations) they also watch for combinations of
mutations (double mutations and triple mutations) and use those to
decipher the pathway.
Some double or triple mutations might have interesting and not
especially disastrous results. How about the toy dogs that are
miscounted and mislabeled? However, any double or triple mutation
that involves a broken metal stamping machine may not be observable
at all. If one combines a broken metal stamping machine with a broken
toy counter, the effects of the broken counter disappear.
A Little Vocabulary Help
Over the years, geneticists have come up with a multitude of new
words and concepts as they analyzed the pathways hidden in
(metaphoric) black boxes by examining the end-products. These new
words make lots of sense to them, but can be mystifying to us. In light
of the Tyras factory, take a look at the following genetic terms and see
if they begin to take on some meaning for you.
Epistasis: when a mutation at the beginning of a pathway completely
obliterates your view of any subsequent parts of the pathway. If the
metal stamping machine has a mutation and fails, we’ll never see the
mutation hiding in the labeling machine.
Modifier: a gene that causes seemingly optional and only slightly
different variations in the output. Some Tyrases may be a little more
desirable than others because they have collars.
Pleiotropy: when a single mistake has far-ranging and diverse
consequences. How many different Tyras types are we getting from the
factory? I count at least six, each pertaining to a particular branching
section of the pathway:
1. Lion-yellow, no collar.
2. Lion-yellow with a collar.
3. Red-gold no collar.
4. Red-gold, without a collar.
5. Broken without a collar.
6. Broken with a collar.
A geneticist would analyze this by looking for how many different
results a particular pathway is producing. If there is more than one
result we call that pleiotropy and we assume that branching pathways
are the cause of it.
Penetrance and Expressivity: two somewhat vague words used by
geneticists when they’re not exactly sure what is going on in the black
box but its very important and very difficult to sort out. Even when we
know that a harmful mutation is present some damaged toy dogs are
less broken or bent then others.
Allele: one of two or more forms of the DNA sequence of a particular
gene. In terms of our assembly line, think of the many possible
different ways there are to modify (improve or break) a machine. Those
are all of its different variants or alleles. In genetics an allele is one of at
least two variations of a gene found at the place where that gene is
located on a chromosome. Scientists often use the terms allele and
mutation synonymously. A mutation can be an improvement in some
way, a simple variation, or can sometimes be detrimental, but is not
necessarily so.
Environment: the contexts in which a gene operates. The immediate
environment in a biological pathway can be disrupted by thousands of
different external factors, just as chemically imbalanced paint could
change Tyras’s color or a tornado could destroy the whole factory.
Additional Layers of Complexity
The factory inside of a black box may seem complex enough at this
point, but there are a couple of more layers of complexity to keep in
mind. First off, there is nothing linear about the real biological
pathways. In Dr. Dyer’s words, they are “convoluted, loaded with
redundant processes, baroque functions, and seemingly nonfunctional”
bits, pieces and distractions. And, there are an unimaginable number of
pathways in each Leonberger’s body.
Remember too, that when geneticists are searching for mutations
they have to methodically work their way through 2.5 billion base pairs
of nucleotides. Only about 2% of the sequences of these DNA units
actually compose codes that the 20,000 genes provide.
We can leave most of this complexity to the scientists that are
working on our dogs’ behalf. Our job is to make sure they have the
resources they need to carry on their work. We can do this by making
contributions to the LHF and participating in calls for Leonberger DNA.
We also need to remind our breeders how profoundly grateful we are
to them for all the work they have done and continue to do on behalf
of the breed. And, make a promise to our dogs that we will continue to
do everything in our power to support researchers who create new
tools for breeders and breeders as they learn to use their new tools.
References
Cieslik, Jürgen and Marianne, Lehmann Toys: The History of E.P. Lehmann-1881-1981, New
Cavendish Books 1982. Printed and bound in Munich, Germany.
Dyer, Betsey Dexter, The Basics of Genetics, Wheaton College, 2009. Recorded Books, LLC.
This article is based on excerpts from Caroline Bliss-Isberg’s forthcoming book, The Complete
Leonberger: A Guide to the Lion King of Breeds.© Caroline Bliss –Isberg 2010