CHIMERAS (Track Presius) (37 page)

THE SCIENCE BEHIND

THE SCENES

A look into Track’s condition

As Watanabe states in CHAPTER 28, Track is an epigenetic chimera. Most people are familiar with genetic chimeras, i.e. two fertilized eggs fused into one morula (the early stages of an embryo), resulting in one indi
vidual with two distinct DNA’s.

Track’s DNA, however, is the same everywhere. That’s because he is an epigenetic chimera, not a genetic one: while his DNA is “normal”,
the types of genes expressed in his cells are different.

For the majority of us, the cells throughout our body carry the same DNA. What distinguishes a brain cell from a skin cell is not the DNA, rather, it is which genes are expressed (“turned on”) and which are not (“turned off”).

How does the body decide which genes should be turned on and which should be turned off?

DNA is packaged inside the nucleus. You can think of it as a messy ball of yarn wound around little spools called histones. Each gene in the DNA carries information to make proteins. Cells depend on proteins to carry on their functions and communicate with one another. In order to make proteins, the information must be read off the DNA and translated into yet another code, the RNA. However, like I said before, the DNA is tightly packaged in the nucleus, in a structure called chromatin.

When it’s time to “make” the proteins, the chromatin reas
sembles itself. The spools (histones) move around and present some genes while hiding others. The genes that are presented are “expressed” and the information is read and transcribed into RNA
1
. The genes that instead remain hidden are not expressed (hence “turned off”).

This is the heart of epigenetics: the mechanisms that ensure what genes are turned off and on in different tissues at different times of our lives. These conformations allow our body to adapt to the environment and, as it has been reported in numerous studies, even though these changes are not encoded in the DNA, they can be inherited for quite a few generations.

Save a few random mutations that accumulate as we age, our DNA stays the same throughout our life. And yet our body has the incredible ability to adapt to the environment: our immune system “learns” to recognize different pathogens. Our brain acquires new skills as needed. On the flip side, immune diseases can arise at some point in our life. We all react differently to the environment because we all have different genomes, different starting points. But the way we, as individuals, adapt as the environment changes around us (i.e. diet, climate, stress, etc.) is orchestrated by epigenetics.

Diet can affect the epigenetic landscape of our body dram
atically. For example, a diet high in fat during childhood will prompt the body to create more storage for the fat and make it a lot harder to lose weight as adults. And this can affect future generations, too. Mouse studies have shown that epigenetic changes induced by environmental stress can last up to four generations
2
even though they are not coded in the DNA.

Human DNA is made of three million base pairs, of which only about 20 percent are used to code genes. Up until a few years ago people believed that the remaining 80 percent was useless, to the point that it was dubbed “junk DNA.”

How did we end up with such huge DNA if all we need is 20 percent of it?

Most of the DNA we carry is historical. As the tree of life grew new branches, it kept the old ones. New genes formed and the old ones were silenced. Not erased from the DNA, but silenced: each gene has a “start” and an “end” that signal where to start reading the information and where to stop. By introducing an “early end” the gene is effectively silenced and will no longer be used to code proteins. By holding on to ancestral sequences that at some point in evolution gave rise to different species, Mother Nature ensures that no information is lost. Who knows, maybe the climate will change again bringing us back to the glacial era. So, just in case, somewhere in our DNA there are genes that generations of environmental pressure and selection could turn on again and grant us survival (as a new species) in such harsh environment.

Take the vomeronasal organ for example: it’s an olfactory sense organ found in all mammals, yet in humans it lost its function, as evolution replaced the chemical stimuli once detected through the sense of smell with visual ones.
We still have the genes that encode the vomeronasal organ, but they are silenced.

Similarly, the genes that allow us to detect sweet flavors are the same across most mammals, yet they are silenced in cats
3
.

It turns out that what was originally dubbed as “junk DNA” is far from junk. Not only does it hold our history, but it’s filled with markers and signals responsible for epigenetic changes. 

So, what happened to Track? Some
of the ancestral genes turned “on” as a result of something that happened in his childhood. Which genes? Well, this is where my poetic license comes in, but if you don’t allow an author his or her poetic license you’ll miss out on the most fantastic premises.

When I started writing
Chimeras
, my driving question was: if we have silenced predator genes in our DNA, what if a sudden life-threatening trauma were to “awaken” them through epigenetic changes? What if those silenced genes were to be expressed again, genes that control our vomeronasal organ, for example?

Chimeras
touches many other scientific topics, besides chimerism and epigenetics. Readers interested in learning more about gene therapy will certainly enjoy
The Forever Fix: Gene Therapy And The Boy Who Saved It
, by Dr. Ricki Lewis.

Feel free to also check out my blog:

http://chimerasthebooks.blogspot.com/

where I cover some recent gene therapy success stories (under the label “gene therapy”) and other topics such as
cancer, oncolytic viruses and telomerase (under the label “science behind the scenes”).

I
f you have additional questions, please don’t hesitate to drop me a line at
[email protected]
.

And please consider sharing your thoughts on the book by
leaving a review on Amazon
. Thanks!

REFERENCES

1
SL Berger.
The complex language of chromatin regulation during transcription
. Nature 447, 407-412 (24 May 2007).

2
Crews D, Gillette R, Scarpino SV, Manikkam M, Savenkova MI, Skinner MK.
Epigenetic transgenerational inheritance of altered stress responses
. Proc Natl Acad Sci U S A. 2012 Jun 5;109(23):9143-8.

3
Jiang P, Josue J, Li X, Glaser D, Li W, Brand JG, Margolskee RF, Reed DR, Beauchamp GK.
Major taste loss in carnivorous mammals
. Proc Natl Acad Sci U S A. 2012 Mar 27;109(13):4956-61.

ACKNOWLEDGMENTS

_______________

It takes one brave author to turn ideas into printed pages. But it takes a lot of people to make those printed pages come to life.

I’m mostly indebted to my patient, smart, and supportive beta-readers: Cristina Rinaudo, Cindy Amrhein, Christi Lane, Karen and Alex Alaniz, Rowan Greene, Nancy Matuszak, Jack L. Pyke, and Kathy Hamm. Many thanks also to firefighter Michael Galassi, for tips on how to get out of fires (which hopefully I’ll never get to use!), and to district attorney Mark Pryor who answered all my legal questions. I owe the accuracy of the autopsy scenes to D.P. Lyle and Peter Cummings, fellow writers and medical examiners/forensic pathologists. A lot of feedback that made this book much better came from literary agent Tris Coburn, my current awesome agent Nicole Resciniti, and Random House executive editor Anne Groell. To all these people go my heartfelt thanks.

No, I’m not forgetting you, Tim. I’m saving you for the best part.

You see, Track Presius would be issuing parking tickets on skid row right now if it weren’t for the one and only, retired LAPD officer and story-teller Timothy Bowen. Not only did Tim introduce me to the LAPD
modus operandi
and lingo; not only did he double-check my plot and police procedural; Tim patiently answered every question I had and added his own stories and anecdotes, bits of which gave life to—well, yes, you’ve guessed it—Detective Satish Cooper. It is also thanks to Tim that I was able to tour the LAPD headquarters, both the old Parker Center and the new one (although the new one is not mentioned in the book because the story takes place in 2008, one year prior to the opening of the new headquarters). If you want a taste of Tim’s hilarious stories I highly recommend reading his memoir (ASIN: B005TAGE4W or check the link on my webpage). But remember: don’t read it in public places unless you don’t mind people staring wide-eyed at you as you burst out in laughter.

Finally, these acknowledgments would not be complete without mentioning my supportive family. My parents always knew I was restless, though I’m not sure they ever anticipated to what extent.
Grazie babbo e mamma
! My husband is my harshest reader and I love him to pieces for that. And to my kiddos I ask for forgiveness as for years they’ve been wondering what mom was doing tied to her laptop until the wee hours of the night. I love them to pieces, too.

ABOUT THE AUTHOR

© E.E. Giorgi 2014

E.E. Giorgi is a scientist, a writer, and a photographer. She spends her days analyzing HIV data, her evenings chasing sunsets, and her nights pretending she's somebody else.
 

BLOG: chimerasthebooks.blogspot.com/

PHOTOGRAPHY: elenaedi.smugmug.com/

GOODREADS: goodreads.com/author/show/7954733.Elena_Giorgi