Caption: In Drosophila females, sequential meiotic stages are observable in a string of developing egg chambers called the ovariole. Meiosis starts at the anterior region (top-right) and meiotic cells form the synaptonemal complex (shown in purple) to pair up homolog chromosomes. Centromeres are shown in orange and DNA is labeled green Credit: Courtesy of Dr. Satomi Takeo, Stowers Institute for Medical Research.
After more than a century of study, mysteries still remain about the process of meiosis—a special type of cell division that helps insure genetic diversity in sexually-reproducing organisms. Now, researchers at Stowers Institute for Medical Research shed light on an early and critical step in meiosis.
The full research, to be published in the Nov. 8, 2011 issue of Current Biology, clarifies the role of key chromosomal regions called centromeres in the formation of a structure known as the synaptonemal complex (SC). “Understanding this and other mechanisms involved in meiosis is important because of the crucial role meiosis plays in normal reproduction—and the dire consequences of meiosis gone awry,” says R. Scott Hawley, Ph.D., who led the research at Stowers.
“Failure of the meiotic division is probably the most common cause of spontaneous abortion and causes a number of birth defects such Down syndrome,” Hawley says.
Meiosis reduces the number of chromosomes carried by an individual’s regular cells by half, allocating precisely one copy of each chromosome to each egg or sperm cell and thus ensuring that the proper number of chromosomes is passed from parent to offspring. And because chromosomes come in pairs—23 sets in humans—the chromosomes must be properly matched up before they can be divvied up.
“Chromosome 1 from your dad has to be paired with chromosome 1 from your mom, chromosome 2 from your dad with chromosome 2 from your mom, and so on,” Hawley explains, “and that’s a real trick. There’s no room for error; the first step of pairing is the most critical part of the meiotic process. You get that part wrong, and everything else is going to fail.”
The task is something like trying to find your mate in a big box store. It helps if you remember what they are wearing and what parts of the store they usually frequent (for example, movies or big-screen TVs). Similarly, chromosomes can pair up more easily if they’re able to recognize their partners and find them at a specific place.
“Once they’ve identified each other at some place, they’ll begin the process we call synapsis, which involves building this beautiful structure—the synaptonemal complex—and using it to form an intimate association that runs the entire length of each pair of chromosomes,” Hawley explains.
Some model organisms employed in the study of meiosis, such as yeast and the roundworm Caenorhabditis elegans, use the ends of their chromosomes to facilitate the process. “These organisms gather all the chromosome ends against the nuclear envelope into one big cluster called a bouquet or into a bunch of smaller clusters called aggregates, and this brings the chromosome ends into proximity with each other,” Hawley says. “This changes the problem of finding your homologue in this great big nucleus into one of finding your mate on just the surface of the inside of the nucleus.”
But the fruit fly Drosophila melanogaster—the model organism in which meiosis has been thoroughly studied for more than a century, and which Hawley has studied for almost 40 years – has unusual chromosome ends that don’t lend themselves to the same kind of clustering.
“So even though the study of meiosis began in Drosophila, we really haven’t had any idea how chromosomes initiate synapsis in Drosophila,” Hawley says. “Now, we show that instead of clustering their chromosome ends, flies cluster their centromeres—highly organized structures that chromosomes use to move during cell division. From there, the biology works pretty much as you would expect: synapsis is initiated at the centromeres, and it appears to spread out along the arms of the chromosomes.”
The ramifications of the findings extend beyond fruit flies, as there’s some evidence that synapsis starts at centromeres in other organisms. In addition, Hawley and coauthors found that centromere clustering may play a role later in meiosis, when chromosomes separate from their partners.
“There’s reason to believe that some parts of that process will be at least explorable and potentially applicable to humans,” Hawley said.
The work also is notable as an example of discovery-based science, Hawley said. “We didn’t actually set out to study the initiation of meiosis; we were simply interested in characterizing the basic biology of early meiosis.”
But postdoctoral researcher and first author Satomi Takeo, Ph.D., noticed that centromere clustering and synaptonemal complex initiation occurred in concert, and her continued observations revealed the role of centromeres in initiating synapsis.
“I was staring with tired eyes at the cells that I was analyzing,” Takeo recalls. “Somehow I started looking at the spots I had previously ignored—probably because I thought they were just background noise—until I saw the connection between centromere clustering and synapsis initiation. After going through many images, I wrote an email to Scott, saying, ‘This is really important, isn’t it??’ With that finding, everything else started to make sense.”
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In addition to Hawley and Takeo, the paper’s authors include Cathleen M. Lake at the Stowers Institute for Medical Research and Eurico Morais-de-Sá and Cláudio D. Sunkel at Universidade do Porto in Porto, Portugal, who provided information on the earliest stages of the process.
“The living entities in this conditioned world are My eternal, fragmental parts. Due to conditioned life, they are struggling very hard with the six senses, which include the mind.” (Lord Krishna, Bhagavad-gita, 15.7)
The rollercoaster ride starts when your connecting flight home gets delayed. This is quite normal, as in the summertime there are intense thunderstorms that quickly travel through different areas. These storms are short in duration but very intense, so trying to take off or land an airplane through them is very difficult. The airline tells you that your flight home is delayed because the airplane that is supposed to take you is currently stranded somewhere else, where there is bad weather. Ah, but if only the frustration stopped there. A few minutes later, you notice that the monitors displaying the time and gate of your flight say “cancelled” underneath your flight’s new scheduled departure time. No announcement has been made, but you decide to get up and visit the ticket counter just in case. After you get on line, they make the official announcement that your flight is cancelled. Now a throng of people is lined up, all essentially competing with one another to get on the next flight, which leaves in an hour.
As the short flight home progresses, you start thinking that maybe the captain was just bracing you for the worst. Thus far there has been little to no turbulence, and the plane is ready to make its descent into the destination airport. This is where things get really interesting. As you start the descent, the turbulence picks up. “Okay, no sweat, right? Obviously we’re going through rainclouds, so that’s why the plane is shaking so much.” As you get further down, however, the shaking and the sudden jolts within the aircraft intensify. As the turbulence seems to reach its apex, you notice something strange. It appears that the plane is heading back upwards. Not only that, but the intensity of the upward motion is quite severe, so the airplane’s interior is not as quiet as it normally is. No one has said anything, so you’re not sure what is going on. Then the turbulence really intensifies. No more is there quiet around you; just utter panic. You start wondering if this is it. The only thing you can compare the experience to is a fighter jet trying to get away from enemy fire. “It’s obvious that we’re now going somewhere else, but why hasn’t anyone said anything?”
What is material existence exactly? Think of being far away from home and not wanting to return because of the difficulty of the journey. The airplane passengers felt comfort when hovering above the rainclouds, but unless the difficult landing was again attempted, they would remain shut out from their real business. Similarly, the individual spirit souls travel through the cycle of birth and death, or 
With the Supreme Lord, however, there is only bliss. This is part of His constitution. Since we come from God, our properties are similar to His, except we don’t possess them in the same proportion. The most auspicious destination, or sugati, for the spirit soul is the company of the Supreme Lord. God is actually situated everywhere, but the material existence is considered separated from Him because His presence is forgotten. God is within every single atom, but unless we realize His presence and take advantage of it, we suffer in ignorance. Therefore the aim of life becomes quite simple. Follow a bona fide system of spirituality and gradually elevate yourself to the position where you’re always thinking about God.
Who is Krishna? The Vedas say that the original Personality of Godhead has a bluish hue and a transcendentally sweet form. He carries a flute in His hands and wears a peacock feather in His hair. Since this form is all-attractive, it can be described by the Sanskrit word Krishna. This same supreme person can then expand into many other personal forms, such as 
