Parasite Eve (43 page)

    She bowed gently, then took
another step forward as the chair unfurled a large beige-colored scroll.

    He leaned into the microphone
and began to read.

    “This award hereby confirms
that Sachiko Asakura has completed the two year Ph.D. preparatory program and
all courses therein to earn her master’s degree in Pharmaceutical Sciences.
Congratulations.”

    He turned around the diploma
180 degrees and handed it to her. Asakura bowed and put out both hands,
accepting it reverently amidst camera flashes.

    She backed up to her left,
then turned to the side and bowed deeply to all of the professors.

    The next name was called. A
voice responded.

    Asakura returned to her seat
with her degree, watching as her classmates’ names were called.

    Following the university’s
graduation ceremony, the Pharmaceuticals students had come back here to their
school for a private assembly, where degrees were given to everyone anew. This
was the day when the normally drab lecture hall overflowed with the beaming
faces of graduates, all in their best suits. Asakura had chosen to wear
traditional attire, lent to her by her mother.

    As she rolled up her degree
and placed it in its tube, a refreshing breeze caressed her cheek.

    She felt overwhelmed with joy
and gazed out the window.

    The weather was clear and
beautiful, plum tree buds already opening in the warm air. The wind carried a
pleasant scent.

    The reality of getting her
degree finally hit her. Having been hospitalized, she hardly performed any
experiments for a good while but did manage to finish and present her thesis.
There was still a burn mark on one part of her body, but the more obvious scars
on her face had been corrected through skin grafting.

    Asakura gazed at her
classmates and reminisced about her school days. She had been through more than
she cared to think, but on the whole it was an enjoyable six years. These last
three in particular, she was thankful to have found her motivation. She nodded
once to herself, thinking how right she was to have chosen this path.

    After the ceremony, they
relocated to the course seminar room for a final get-together.

    They all celebrated with some
beer, then focused their attention on Ishihara, who said: “On behalf of all the
staff, I wish to congratulate you all. Most of you will now move on to
pharmaceutical companies or research institutions. But no matter what path you
choose, I believe that every one of you already possesses enough knowledge to
go anywhere with nothing but the highest confidence. Even if you choose company
work, I hope you will dedicate yourselves to making full practical use of all
you’ve learned here and that you make significant contributions to our field.
And I have no reason to doubt that you all will.”

    The graduates smiled brightly.

    “And to all you seniors,” the
professor said, raising his voice, “the state pharmaceutical exams are coming
up in approximately one week. I don’t care how much you drink today, but
starting tomorrow I want to see every nose in a book.”

    Everyone laughed at this.
Even Asakura looked to her friends and snickered. The professor made this same
joke every year, but it never missed.

    “In any case, bottoms up!”
Ishihara raised his glass.

    “Bottoms up!”

    At once, the room filled with
noise and excited chatter. Flashes went off everywhere. Everyone gathered for a
group shot as well. More beer was brought out and hors d’oeuvres were added.

    Asakura chatted with her
friends, then mingled around to greet the various professors to whom she was so
indebted. She felt lonely to be parting from these people, but at the same time
everyone seemed so relieved to be moving on. Asakura’s sadness was comfortably
placated by a mild tipsiness.

    Halfway through the party,
she ducked out quietly and went to the Biofunctional Pharmaceuticals office on
the fifth floor.

    Since everyone was
downstairs, there was no one else there. She opened the door to the lab, a
place where she had spent so much of her time over the past three years.

    She looked inside, only to
notice that a number of the machines had been left running. Someone was
probably doing a PCR,
[38]
since the
thermal cycler
[39]
was on.

    She stood in front of her
desk and ran her fingers gently along its now empty surface. Asakura had
already brought her Mac back to her apartment and was finished with packing.
She was struck by how vast her desk seemed with nothing on it.

    She glanced over at her
bookrack, where the year’s issues of
Nature
were being stored. They had
been purchased by the course and were normally kept in the seminar room.
Asakura was unsure why they had been moved here, but maybe they were remodeling
the room and were taking advantage of the available space left from her
absence. She stared at the perfectly lined spines, then plucked one out from
among them.

    She flipped through it and
opened to the articles section.

    The article was written in
English, under which the names Toshiaki Nagashima, Sachiko Asakura, and Mutsuo
Ishihara were printed. It was Toshiaki’s piece.

    She gazed at the page. Her
data was printed as diagrams, to which long footnotes were attached. The images
somehow seemed to her the remarkable work of some other person. She felt
flattered.

    It was only a short
two-and-a-half page article. Even so, it was the pride of the Biofunctionals
course.

    But she had not truly
appreciated it until now.

    She would probably never have
her name mentioned in Nature again. And her one time was thanks to Toshiaki.

    If only Doctor Nagashima were
still alive.

    Asakura clutched the magazine
to her chest.

    Toshiaki’s face appeared
before her. At that moment, her eyes began to sting with unexpected tears.
Surprised at herself, she wiped her cheeks, smudging her makeup. But the tears
kept falling. She did not even shed a tear when she broke up with her
boyfriends in high school. She tried laughing to mask her unusual outburst of
emotion, but managed only a damp sigh. She sniffed and tried to smile away her
sorrow.

    She opened to the “NEWS AND
VIEWS” section and turned to a piece of commentary. Memories of the day she
learned of Toshiaki’s death came flooding back.

    She’d read this short article
when the magazine first came out, but had forgotten about it. While in the
hospital, she learned in great detail from the police and classmates what Eve 1
had done. She knew that Eve 1’s mitochondria had rebelled, that the recipient
girl was forced to give birth, that the child unexpectedly morphed between male
and female, and that in the end Toshiaki and the new birth melted into one
another and perished in flames. When Asakura first heard about this, she did
not understand why the mitochondrial child had died. But then, she remembered
the theory presented in this article.

    It had always been accepted
that mitochondrial DNA was passed through maternal heredity. Though male
mitochondria entered an egg via the sperm which carried them, they did not
multiply afterwards, and the mitochondria carried by the conceived child were
once thought to have all been maternal. Genetic researchers accordingly
analyzed mitochondrial DNA with this “matrilineal” rule in mind, and it indeed
became a useful tool for theorizing the rate at which evolutionary processes
occurred.

    But in 1991, a certain
research group announced some shocking results. When different species of mice
were crossbred, it became clear that there was paternally transmitted
mitochondrial DNA in their offspring. Though only a trace amount, its presence
was unmistakable. The article undermined everything and was the subject of much
attention. Since then, other researchers debated about whether or not
mitochondrial DNA was actually unisexually inherited. Then, more recently, the
problem had finally been clarified.

    The results, in simple terms,
were as follows:

    In instances of interbreeding
among identical species, the father’s mitochondrial DNA entered the egg via his
sperm, but after a certain amount of time, it died out, presumably neutralized
by the placenta. In other words, the father’s mitochondrial DNA was ultimately
not inherited by the birthed child. However, when different species were
crossbred, the opposite was true. The offspring’s mitochondrial DNA was found
to be 56% paternal.

    Asakura thought that probably
Eve 1’s sole intent in breeding with Toshiaki was to acquire his nucleus so
that she could create a new species with it and her mitochondrial DNA. But
while Eve 1 was being cultivated in the lab, it had developed into a non-human
species. The mating of Eve 1’s egg cell with Toshiaki’s sperm was essentially
an interspeciary crossbreeding. Toshiaki’s mitochondrial DNA grew inside the
egg to drastic results.

    Asakura skimmed through the
Nature
article. She had come back to it numerous times since leaving the hospital.

    It was a summary of the
hereditary pattern of mitochondrial DNA observed in a species of the blue
mussel family. In the case of this species, the father’s mitochondrial DNA was
passed on to children, but the method of transmission involved was found to be
incredibly unique. Unlike humans and lab mice, males carried masculine
mitochondrial DNA and females carried feminine mitochondrial DNA. When the two
mated, something peculiar happened. Though the sperm contained male
mitochondrial DNA and the egg contained female mitochondrial DNA, female
offspring inherited genes only from the female mitochondrial DNA, while male
offspring inherited an equal amount of genes from both. As the male offspring
grew, the male mitochondrial DNA multiplied within it and ultimately
established dominance. In other words, unlike with mice, what occurred with
mussels was “uni-parental transmission.” Female mitochondrial DNA was only
inherited by female mussels, and male mitochondrial DNA only by males.

    One explanation claimed this
was a defense mechanism to combat the “selfish” dispersion of mitochondria. Let
us say there has been a single mutation in mitochondrial DNA in a single female
mussel, a mutation that dramatically speeds up the rate of its DNA replication.
It would begin to proliferate in the mussel and continue to do so in its
children, driving out the original female mitochondrial DNA. If maternal
mitochondrial DNA were transferred to both sons and daughters, this altered DNA
would spread through future generations. But if female DNA were inherited only
by female offspring, the altered DNA would only be transmitted through the
daughter’s lineage. The mutation would be better contained. Introducing Richard
Dawkins’ concept of the “selfish gene” into this discussion opens up an
interesting vista.

    Dawkins’ basic idea is that
“all that a gene wants is to leave copies of itself in as many descendants as
possible .”In the case of the mussels, we have three such selfish players, the
nuclear DNA, male mitochondrial DNA, and female mitochondrial DNA. The mutated
female mitochondrial DNA, wanting nothing more than to proliferate as much as
possible, will replicate itself rapidly to pass itself on to as many
descendants as possible. But the male mitochondrial DNA doesn’t want to be
exterminated and will try to obstruct the propagation of the mutant female
mitochondrial DNA. Moreover, the nuclear genomes in the mussels might not favor
mutations in mitochondria with which they’ve enjoyed a working symbiotic
relationship. If mitochondria changed too quickly, the host’s very survival
could be threatened. The female mitochondrial DNA’s selfishness is, in this
way, at odds with the self-interest of the two other players.

    This was perhaps why a mechanism
had arisen to keep female mitochondrial DNA in check. Perhaps something similar
had happened in the thing born from Eve 1. Asakura certainly thought so.

    The fertilized egg had
received “evolved” mitochondrial DNA from Eve 1, whereas from Toshiaki,
“normal” mitochondrial DNA was transferred, even if in a miniscule amount. But
these two sets of genes coexisted in the new life form. The mitochondria in Eve
1 undoubtedly believed they had facilitated evolution by their own power
alone.. In actuality, paternal mitochondrial DNA had also played a role in
mitochondrial evolution, but Eve l’s mitochondria had failed to see this. Eve 1
had not counted on Toshiaki’s normal mitochondria being inherited by their
daughter.

    The normal mitochondrial DNA
transmitted into their child must surely have feared being utterly destroyed by
the evolved DNA. The normal DNA’s egotism, which wanted nothing more than to
leave descendants, flatly opposed the agenda of Eve 1’s more advanced
mitochondrial DNA. A violent battle ensued between the two sets of genes,
eventually leading to their mutual destruction.

    This was as good a guess as
Asakura could make. No one would ever know the full truth. People’s knowledge
of mitochondria was still incredibly limited. Mitochondrial research was only
just beginning.