The protein I have been focusing on this week is called Mad 2. It is thought to be involved with a checkpoint in cell division that prevents the cell from going through division until all the chromosomes are properly attached to the meiotic spindle. Then they can be dragged apart, leaving each new daughter cell with a copy of each chromosome. If something goes wrong with this process chromosomes may be left behind or both copies will end up attached to only one end of the spindle complex and one of the daughter cells will end up with both copies of the chromosome. Mad 2 may be a protein that serves as a “wait for me” signal that unattached chromosomes release to keep the cell from dividing without them. This week, we “turned off” the genes that code for Mad 2 with a morpholino solution we injected into starfish oocytes (just like I talked about with the Anillin in the week 3 blog post). We then viewed them with a Hoechst dye which highlights DNA under certain light conditions. Below is a photo I took which shows the nuclei of a blastula (fertilized egg that has divided until it is a hollow ball of cells).
We also injected some of the oocytes with two fluorescent probes to allow us to see microtubules and DNA under the confocal microscope. This allowed us to look for abnormalities in the cells deprived of Mad 2. Below are some examples of the type of videos we are able to make.
In this video you can watch the cell undergo second meiosis. The chromosomes are seen in blue and the microtubules in yellow. The cell halves its DNA and then pushes it out into a polar body.
In this video you see the cell's first division. First the microtubules deposited by the sperm pulls the oocyte's pronucleus towards its own. Then the DNA in the nucleus is wound into chromosomes and pulled apart by the spindle fibers. At the very end you can see the cell start to cleave in two.
The babies are still growing along, but I haven’t had much time to look at them. Claire, my fellow intern, took some wonderful photos of our baby phoronids though. Their little tentacles are getting so long. If you want to know more about the development of our little larva Claire has a great blog on their development which she posted last week.
See You Next Week!
Thanks so much for reading. For all of you who made it to the end: I give you a photo I took last weekend while car camping at Mount Hood.
My name is Nicolle Koontz and I am from Grass Valley, California where I attend Sierra College. I am lucky enough to be working in George von Dassow's lab doing research on the cellular biology of starfish oocytes during mitosis. I am an information addict. I have to know how things work, how we know how those things work, and why they work the way they do. These sorts of questions have led me to major in Biology. As an REU intern I look forward to working in a state of the art lab with mentors and grad students who share in my joy of discovery while also building my skill set. I am so excited to dive into a project that can contribute to our collective scientific understanding of the world.