parasitism eve

Chapter 12

"Like other parasites, intestinal bacteria also live in our bodies, obtaining nutrients from us, their hosts, to sustain life. However, as mentioned earlier, intestinal bacteria are very beneficial, providing us with vitamin K. This relationship where different organisms live together and benefit from each other is called symbiosis. Although intestinal bacteria are parasites, they are essential to us. So, are intestinal cells the only ones we coexist with? Of course not. Now we finally arrive at the main topic of this lecture, a name you should have encountered in high school science classes: 'mitochondria'." "The body." In fact, we've discovered that mitochondria are also a kind of symbiotic parasite. Of course, mitochondria aren't insects, and strictly speaking, the term "parasite" doesn't apply, but they do have something in common: they both live in symbiosis with us, their hosts. Through research on mitochondria, we've also learned a great deal of interesting knowledge about ourselves. Our lectures are based on research related to mitochondria. Today, I'd like to talk to you about the symbiotic relationship between mitochondria and humans." Professor Ishihara paused here, gesturing to the staff member in the center of the room who was projecting the slides.

The projector's cooling fan started spinning, and at the same time, the lights in the room began to turn off one by one from front to back. "Perhaps a staff member is operating the switches," Shengmei thought to herself, turning her gaze back. Then, a familiar face came into view.

A man was sitting three rows behind Shengmei. Shengmei's gaze was fixed on him, trying to figure out who he was, but because the room was dimly lit, she couldn't see his face clearly. The man seemed to notice Shengmei's gaze and looked over. Shengmei felt a little embarrassed and quickly turned her head back to the front. A huge diagram of cell structure was displayed on the screen.

"This is a simplified diagram of a human cell," Professor Ishihara explained, holding a laser pointer that emitted a red light. "The nucleus is located in the very center, containing chromosomes and a large amount of genetic information. The oval structure here is the mitochondria. As shown in the diagram, it has an outer membrane and an inner membrane, with the inner membrane being folded. I think everyone is familiar with this diagram because you probably learned about it in middle school. Textbooks depict mitochondria as oval-shaped like this, but in reality, mitochondria do not look like this. You probably can't even imagine their true shape. Okay, please put down the next slide."

The painting switched to another image. At this moment, those present let out a soft gasp of surprise.

"This is what mitochondria really look like."

The image of the cell filled the entire screen. Faint diamond-shaped outlines emerged against a pitch-black background, within which countless shrunken, thread-like tissues were stained green. Upon closer inspection, they all pointed regularly upwards, as if about to undulate in perfect unison. In the center of the cell, presumably where the nucleus was, was a dark bulge. Shengmei knew this was the appearance of mitochondria in a living cell, stained using some method, under a microscope. A single cell contained dozens, even hundreds, of such mitochondria. Their magnificent form was more beautiful than the folds of velvet. Shengmei's previous impressions of mitochondria were instantly forgotten.

"thump".

My heart started reacting again.

"thump".

Once again.

That's it. Saint-Mei discovered it.

The heart's response is due to this; the heart becomes abnormally excited by the mitochondria.

But why is that?

Saint-Mei's eyes were fixed on the screen. Her irregular heartbeat made her breathing erratic, and she couldn't catch her breath. However, Saint-Mei remained motionless, staring at the huge image of mitochondria, even forgetting her habitual action of pressing her hand to her chest.

The screen switched to the next image, displaying numerous photos of stained mitochondria. The mitochondria, dyed blue and green, took on various shapes: some swollen, some twisted, some fused together, some torn into fragments—a diverse array of forms. Shengmei was captivated by the postures of these mitochondria. Looking at these winding mitochondria, so similar to E. coli, Shengmei finally understood why mitochondria were called parasites.

Professor Ishihara explained in detail that mitochondria also contain DNA, but it is not the same type as the DNA in the cell nucleus. This indicates that mitochondria are descendants of bacteria that once parasitized cells... In the distant past, when our ancestors were still single-celled organisms, mitochondria invaded them and have coexisted with us ever since. "Here, I'd like to briefly recount the evolutionary history of cells. It's generally believed that life first appeared on Earth between 3.9 and 3.17 billion years ago. The earliest life forms were extremely simple in structure, consisting of a soft membrane encasing DNA. They lived near underwater volcanoes, feeding on hydrogen sulfide emitted by the volcanoes. At that time, there was almost no oxygen on Earth. However, from these primitive life forms evolved a type of organism called cyanobacteria. These are the ancestors of modern chloroplasts, capable of producing sugars and releasing oxygen through photosynthesis. These cyanobacteria proliferated rapidly, filling all the oceans around the world about 2.5 billion years ago. Subsequently, the oxygen content in the sea and atmosphere increased, which made life difficult for those primitive bacteria that fed on hydrogen sulfide. Unlike us, they were anaerobic; oxygen was toxic to them. Therefore, the living space of these primitive bacteria was constantly squeezed by the cyanobacteria, gradually shrinking to a very small area near the volcanoes. They could only..." They continued their quiet lives there. Then, the emerging aerobic bacteria took center stage. The oxygen produced by blue-green algae filled the entire ocean. Some organisms considered whether they could use this oxygen to produce the nutrients they needed. These were aerobic bacteria—the ancestors of mitochondria. Because these bacteria knew how to utilize oxygen, the energy they produced far surpassed that of ordinary bacteria. What did producing energy mean? It meant being able to move around freely. These bacteria swam back and forth in the sea. A billion years ago, a major event occurred. Anaerobic bacteria, barely surviving near volcanoes, were invaded by aerobic bacteria. The aerobic bacteria may have initially intended to feast, but they soon abandoned this idea and eventually settled within our ancestors. From that moment on, mitochondria began their symbiotic relationship with us. An electron microscope image of mitochondria appeared on the screen. The mitochondria in the center of the image was in a state of division; the middle section was concave and about to break apart. Inside the mitochondria was a dark mass, precisely in the center of the concave area, seemingly ready to split in two. Professor Ishihara explained that this is mitochondrial DNA. Mitochondria divide and multiply within the cell. The DNA within the mitochondria is also replicated and distributed to two newly formed mitochondria. This process is no different from that of other bacteria. Seimei believed that the mitochondria were alive, residing within her own body, and undergoing division. "Can everyone accept this scenario? Mitochondria played a crucial role in our evolution to this point. Our ancestors lived in symbiosis with mitochondria, thus gaining enormous energy. From then on, cells, originally anaerobic, became oxygen-loving, greatly enhancing their mobility. This allowed cells to obtain nutrients on their own, no longer needing to wait passively for nutrients to drift by. Because cells could use their energy to move to nutrient-rich areas, our ancestors possessed a new ability: the ability to think about hunting. How could they quickly and effectively obtain the nutrients they needed? To solve this problem, life gradually developed advanced thinking abilities from simple neural activities such as reflexes and instincts. On the other hand, it is generally believed that, in addition to mitochondria, cyanobacteria also entered cells during this period. What was their situation? As long as there was light, they could produce nutrients within themselves, so they didn't need to search for prey or have any particular need for thought. All they had to do was expand their surface area to obtain more sunlight. You've probably guessed it already—they evolved into plants." While this might oversimplify the issue, it should help everyone understand the difference between animals and plants. It can be said that it is precisely because of this symbiotic relationship with mitochondria that we can function and think as we do now.” Professor Ishihara explained, pointing to a diagram of the evolutionary tree illustrating the process of biological evolution. On the tree, the main trunk of “ancestral eukaryotes” intersects with “mitochondria,” branching into three branches: “plants,” “animals,” and “fungi.” The “plants” branch also meets “chloroplasts,” which branched off from “blue-green algae,” halfway through. Seimei felt that the “mitochondrial” trunk in the diagram appeared particularly strong. The image on the screen then switched back to a picture of mitochondria. Professor Ishihara continued, “However, modern mitochondria cannot proliferate arbitrarily according to their own will. It is not yet clear how mitochondria divide, but research indicates that mitochondrial proliferation is controlled by nuclear genes. When mitochondria first enter the cell, the genetic code that enables their proliferation should be recorded on their own genes. However, mitochondria quickly transfer these codes to the host cell's nuclear genes.” Therefore, mitochondrial DNA now stores only a very small amount of genetic code. Mitochondria have delegated all the genetic information related to their own proliferation and the production of their building blocks—proteins—to the cell nucleus. This allows mitochondria to dedicate themselves entirely to energy production. For mitochondria, leaving all the complexities to the nucleus allows them to live a comfortable and easy life. The host cell arranges and manages the raw materials for energy production, such as sugars and fats, without the mitochondria needing to worry about anything. On the other hand, from the host cell's perspective, as long as the raw materials for energy production are provided, the mitochondria will produce energy at a level they could never produce themselves—a pretty good deal. In other words, just like the mutually beneficial relationship between humans and intestinal bacteria, host cells and mitochondria have maintained a healthy symbiotic relationship since ancient times.

At this point, Professor Ishihara took a breather, picked up the water glass on the table, and took a sip.

Saint-Mei's heart was pounding so hard it felt like it was about to burst out of her chest.

She hadn't even noticed that her lips were slightly parted, and she was breathing heavily. Because the professor on stage hadn't spoken yet, Shengmei only then realized the sound of her breathing. She quickly swallowed and closed her mouth, but the tremor in her chest didn't subside immediately. After closing her mouth, the air exhaled rhythmically from her nose—Shengmei felt embarrassed and quickly covered her nose and mouth, trying to minimize the sound. She closed her eyes and took a deep breath. Shengmei didn't understand why she was so excited, why she was so obsessed with mitochondria. Why? She couldn't understand. "Thump," "thump," "thump." Her heart was still pounding, her forehead was covered in sweat, and her chest and inner thighs were soaked with sweat, her clothes clinging to her body. Shengmei wiped the sweat from her forehead with her fingers, feeling only a sticky residue. Shengmei opened her eyes, took a handkerchief from her bag, and wiped her forehead and neck. Looking at the screen again, Professor Ishihara had already shifted the topic to mitochondrial DNA.

As we age, abnormalities can occur in the DNA within our mitochondria. These phenomena appear to be related to a substance called reactive oxygen species (ROS). The professor cited several diseases caused by abnormalities in mitochondrial genes. Then, Professor Ishihara discussed how mitochondrial genes are passed down from generation to generation.

"Interestingly, mitochondrial genes are maternally inherited. During fertilization, although the sperm's mitochondria also enter the egg, under normal circumstances, the paternal mitochondrial DNA brought by the sperm does not increase in the fertilized egg. Because only the maternal mitochondrial DNA can increase, the vast majority of mitochondria in a newborn are identical to those of the mother. Therefore, it can be said that mitochondrial genes are maternally inherited. However, this does not mean that all diseases caused by mitochondrial gene abnormalities are maternally inherited. The work of unraveling this mystery is currently underway, and it is one of our research topics. Recent studies have shown that the inheritance of mitochondrial genes is not entirely maternally inherited... Of course, to explain this in detail would be too complicated, so we will not discuss it today."

The photos on the screen gradually decreased, replaced by brightly colored charts. These computer-generated diagrams were far less impactful on Seimei than the previous microscopic photographs. The presentation on mitochondrial genes lasted about five minutes. Unbeknownst to her, the intense tremors in Seimei's chest had gradually subsided. After a while, her heartbeat calmed down, returning to normal. Seimei breathed a sigh of relief. She adjusted her posture, trying to refocus on Professor Ishihara's explanation. Professor Ishihara was about to change the subject.

"...I think everyone feels a lot of pressure while working, studying, and interacting with neighbors. Some say modern society is a society of pressure. Because we always live with others, the generation of pressure is unavoidable. It can be said that the same situation will occur in the symbiotic relationship between host cells and mitochondria. When different types of organisms live together, pressure will arise. In fact, once a cell feels pressure, a substance called stress protein will be produced inside the cell. We now know that this stress protein can coordinate the symbiotic relationship between the cell nucleus and mitochondria."

Cells contain various stress proteins. These stress proteins are responsible for transporting enzymes to the mitochondria. Without these stress proteins, the mitochondria will malfunction. Professor Ishihara explained this in detail with vivid diagrams.

Saint-Mei's heartbeat returned to normal. She glanced at her hands; they were still clenched into fists, the fists she had gripped so tightly during the attack still not relaxed. Saint-Mei gave a wry smile and loosened her fists. She moved her hands around a couple of times to relax her tense muscles.

At this point, the screen switched to a large bar chart. Professor Ishihara explained that this was the result of an experiment he had presented in his lecture. The chart showed the input of enzymes into the mitochondria under conditions of stress protein deficiency. The horizontal axis listed the names of various stress proteins, each with a corresponding bar. Some of these bars were long, while others were short.

"This shows that if a certain stress protein is missing, the amount of enzymes in mitochondria will decrease. This could potentially lead to certain diseases caused by decreased mitochondrial function."

Section 31

Seimei stared intently at the screen. Her gaze followed the red light emitted by Professor Ishihara's laser pointer as she pondered the meaning of the bar chart.

As the professor finished explaining the picture and was about to put down a slide, Saint-Mei's gaze inadvertently caught a detail the professor hadn't pointed out: a line of small English text in the lower right corner of the image.

In that instant, "thump!" Saint-Mei's heart skipped a beat.

The change came too suddenly, and Saint-Mei let out a soft scream.

With a click, the projector displayed another bar chart on the screen. Seimei quickly scanned the image from all angles. The same text was written below this chart. Seimei's heart pounded again. Professor Ishihara was speaking, but Seimei could no longer hear him.

"Click," the screen switched again. It was another bar chart, and the same text was still written in the lower right corner.

A third wave of shock washed over her. This time, Saint-Mei's body jolted from the chair with a loud thud. Everyone in the room turned to look at Saint-Mei, but she was now completely unable to control her body or maintain her dignity. Saint-Mei's heart was pounding wildly. She pressed her hand to her chest, trying desperately to endure the onset of pain, but she couldn't. Saint-Mei opened her mouth, trying to speak, but only managed hoarse, jagged sounds. She was having difficulty breathing, and her cheeks were burning.

"Thump, thump, thump, thump, thump," her chest felt like it was about to burst with steam. Saint-Mei desperately tried to piece together a clue from her chaotic mind: what had happened? A line of small English text appeared on the screen, but Saint-Mei couldn't read it aloud completely, and she didn't quite understand the meaning of the letters. What did it say? Saint-Mei tried her best to recall that string of letters she had only glanced at. The scene before her blurred. It seemed like someone had run towards her.

She remembered! Her pulse pounded in her head, and the English text flashed through Shengmei's mind: Nagashima, T, et al., J. Biol, Chem., 266, 3266, 1991.

I remember now. NAGASHIMA·T, that name sounds familiar. T. "Thump." TOSHIAKI. That's right! "Thump." NAGASHIMA·TOSHIAKI. "Thump." I feel like I've heard that name somewhere before. I feel like I've seen this person somewhere before. This person… I remember now, it was when I first entered university…

"Thump," "Thump," "Thump."

"Are you alright?" A voice came from afar. It sounded like someone was about to pick up Shengmei.

In the instant before she lost consciousness, Saint-Mei saw that person's face. Ah, it was him!

At the same time, another voice came from the depths of her heart: (It is—him—)

A violent spasm spread throughout her body. Saint-Mei buried her face in the man's arm, leaning her convulsing body against him. Who was it? Before she could even ask a question, Saint-Mei fainted.

"Parasite Eve"

Chapter Twelve

About a week ago, the doctor allowed Mariko to walk upright. Because she had been bedridden and weak, her legs felt a little unsteady. However, it was much better than lying motionless in bed enduring back pain. From her bed, Mariko could only see white walls and some medical equipment. Now, walking past the windows, she could finally see the hospital courtyard in the center. The sun was shining brightly, and the vibrant green of the trees was almost dazzling. After looking at it for a while, Mariko felt the heat from outside seeping in, and she started sweating. Starting three days ago, Mariko's activity area expanded. Previously confined to her ward, she could now walk around the building. Tomorrow, her range would be further expanded to the hospital shop, and she could even take a shower. Dr. Yoshizumi and the nurses were exceptionally happy about Mariko's successful recovery. However, to Mariko, this seemed like an exaggerated and empty performance. Her mood grew even colder. Everyone racked their brains to cheer Mariko up. However, all their good intentions were in vain.

That night, Mariko's father came to visit her in the hospital.

As usual, he was dressed in a suit and tie. Mariko wondered to herself, "Doesn't he feel hot dressed like that? Is the air conditioning on in the office?"

The father gave a forced smile and raised a hand to greet Mariko. "...How are you feeling?"

—The same old lines. Why ask questions about things that are obvious at first glance? Mariko found it disgusting.

"What do you want? What books do you want to read? I'll buy them for you."

Mariko knew that her father's smile was fake. She said impatiently, "Give me the money."

"……What?"

The unexpected questions and answers left the father somewhat bewildered.

"The doctor said the money can be taken to the hospital shop tomorrow. I can buy whatever I want myself."

The father didn't say anything. Then came a long silence.

After a while, a low, muffled sound came from somewhere. It might have been the sound of car exhaust, or the sound of the air conditioner; it was hard to tell. After the sound disappeared, the father sighed heavily.

“Mariko,” her father said, “why are you so stubborn? Tell me. I beg you, I beg you!”

"..."

"Weren't you happy during the last transplant? After you were discharged from the hospital, Dad thought you really enjoyed going to school. Why are you so unhappy this time? Do you hate the transplant? Or do you think dialysis is better? What's going on? Say something!"

"..."

"Mariko..."

Perhaps unable to tolerate Mariko's silence any longer, the father raised his voice. Then, he fell silent again. The same sound from before seemed to come from somewhere else.

Section 32

Mariko couldn't understand why her father wanted to give her his kidney. She just couldn't figure it out.

"dad……"

The father suddenly raised his head.

"Was Dad's willingness to give me his kidney truly from the bottom of his heart?"

"What are you saying...?"

The father looked somewhat flustered by the question. Mariko did not miss his expression at that moment.

Mariko stared at her father's face. This time, it was her father who wanted to avoid her gaze.

"Actually, Dad was very unwilling, right? You felt it was a lot of trouble for you that I got this disease, didn't you? If Mom were still here, we could have used her kidney, didn't you think so? She donated her kidney, but because of me, the transplant failed, and then..."

"shut up!"

Then I heard a "snap" sound.

A burning pain shot through Mariko's cheek. For a moment, Mariko herself didn't know what was happening.

Looking at her father again, she saw that he had his head down and his body was trembling uncontrollably. From Mariko's angle, she couldn't see her father's face hidden in the shadows, but he seemed to be muttering some words he couldn't hold back.

After a while, the father went home.

Mariko lay on the bed, staring blankly at the dim ceiling. Every now and then, a faint buzzing sound reached Mariko's ears; if she listened carefully, it sounded like the rolling of magma underground.

"Anqi was discharged from the hospital and came back today."

During morning extracurricular activities, the teacher asked Mariko to stand in front of the classroom door.

The students in the class immediately focused their attention on it. Those sitting in the front all looked up, as if they wanted to see it very clearly, while the boys in the back stretched their necks and strained to see what was in front of them.

“Anqi received her father’s kidney and underwent a transplant. Although she can’t participate in strenuous exercise for the time being, from now on, Anqi can eat meals with everyone at school, and after-school activities will not be a problem. I hope everyone will help Anqi catch up on the schoolwork she missed during her hospitalization. Please also tell her where our classes are now.”

Mariko was a little shy. She kept her head down while the teacher spoke, but inside she was filled with the joy of returning to school. It was so much fun being with her friends!

Without realizing it, Mariko sensed something moving in the classroom out of the corner of her eye. Looking over, she saw a female classmate smiling and making exaggerated mouth movements, conveying information to Mariko word by word.

"Congratulations," she "said," but didn't say anything.

Mariko laughed, and when the teacher wasn't looking, she also tried to mouth "thank you".

School life was filled with joy, and her friends cared deeply for Mariko. Although the curriculum progressed quickly, and she struggled to understand math and other science subjects, her friends lent her practice problems for reference, allowing her to keep up. Mariko's life had suddenly returned to what it was like before she underwent dialysis, but what pleased her most was that she could do everything just like her classmates. However, she couldn't engage in strenuous exercise during PE class and her twice-daily exercise sessions. She needed to be observed for a while until her kidneys fully adapted to the new environment.

At that time, the physical education class was swimming. Mariko sat on the "cold bench" by the pool, watching from afar as everyone jumped into the water with great energy. The students played water fights, and sometimes the splashes would hit Mariko.

Watching everyone swim freely, Mariko felt a dull ache in her lower right abdomen. She gently placed her hand there and touched it, feeling something like a lump inside. Mariko thought, "It must be my father's kidney."

Mariko's abdomen bears a clear surgical scar. The skin at the suture site is taut, forming a jagged bulge, resembling a large centipede. It moves with every twist of her waist. Mariko hates this scar. Her father's kidney is located directly below it. Although a long time has passed since the surgery, Mariko always feels an inexplicable awkwardness about the transplanted kidney. She doesn't usually notice it, but when she sees her male classmates' bodies during swimming lessons, Mariko becomes aware of the scar on her lower abdomen. Despite her reluctance, Mariko has to admit that she has received a transplant. Once Mariko thinks of this, the scenes of her hospitalization and a series of memories about dialysis resurface in her mind. She can't eat her fill of delicious food at once; she has to rush to the hospital in the middle of the night; not only can she not watch the TV programs that everyone else is watching in the hospital, but she also has to sleep with her arms outstretched; the most painful thing is that even the amount of water she drinks is restricted, and she can't remember how many times she fantasized about the pleasure of drinking freely. After Mariko noticed the movement in her kidneys, the feeling didn't disappear until the end of the swimming lesson.

Mariko wondered to herself, why does it hurt so much?

Could it be that my father's kidneys are incompatible with my body?

Mariko broke out in a cold sweat.

If the nephritis flares up again, and if the kidneys fail, will I have to go on dialysis again? And then I won't be able to eat the things I want to eat anymore?

The consequences are unimaginable. That won't happen. She doesn't even want to think about it. Whenever she starts to let her mind wander, Mariko quickly shakes her head. The crucial problem is that her father only has one kidney left. If the kidney implanted in her body malfunctions, where will she find a replacement? Yes. There was no way out.

Dr. Yoshizumi explained that if one were to wait in line for a donor kidney, the process would continue until a matching donor was found. Hearing this, Mariko registered as well. She figured her father might be angry if she said she didn't want a transplant, so she decided to just put her name on the register. That was what Mariko thought at the time. Actually, Mariko wasn't sure if she truly wanted another transplant, and for a long time, she had tried her best not to think about it.

During dialysis treatment, recalling the first transplant would cause her heart to ache as if it were being stabbed. At such times, Mariko would close her eyes and clench her teeth. Back then, she could eat such delicious food; back then, she was so happy… These thoughts kept popping into Mariko's mind. She simply couldn't stop them.