Post by Ghost of Fire (Fëanáro) on Sept 5, 2012 23:41:02 GMT -8
((All copyright to Ghost at RMW, and to Prof Solly, whose class this was written for))
A Cell’s Take on Neuroblast Formation in Drosophila: An Overview
It goes without saying that for all major decisions, the vast majority of those deciding like to have someone else to talk things over with, to, if nothing else, offer reaffirmation that the decision reached is, in fact, the correct one. That this is true in humans can be deduced simply from a study of human behavior, but there are other deciders, and other decisions to be made.
Parvani Aralyn Loky Mallen was a most distinguished cell. He, or she, for it doesn’t really matter when one refers to cells, as they don’t care about such trivial, to them, aspects. We will call Parvani Aralyn Loky Mallen a she, for this fits the traditional classifications of mother cell and daughter cells, which have been used in biology for many long years. Now, after the manner of the well-to-do and (yet) polite individual, Parvani Aralyn Loky Mallen was on great terms with her neighbors. They spent countless periods together, talking and sharing the headlines in Signals This Period and Letters from your local HOX cluster. This latter was a very popular read, for it informed Parvani Aralyn Loky Mallen and her neighbors of where they were located, relative to the rest of the organism.
Parvani Aralyn Loky Mallen lived with her neighbors, along with many other distinguished well-to-do cells, in houses that made up thick rows (or maybe stripes would be better) along either side of a small street called Ventral Midline Way. The houses on one side of the street (where Parvani Aralyn Loky Mallen lived) were part of hemisegment A; those on the other side were part of hemisegment B. These houses, for though cells have a membrane and thus do not need houses, they much prefer to call the area wherein they stay their “house”, were part of the neurogenic zoning area, meaning that only special ectodermal cells were allowed to live there — mesoderm and endoderm cells had to find lodging elsewhere.
Now Parvani Aralyn Loky Mallen was very intelligent, she was a 3.99 student at the local college, Neurectoderm School for Potential, where she and her friends studied in the hopes of being selected to be a neuroblast, and thereby having a chance of becoming neural cells, though most of them, as is the sad fate of life, would end up serving in the Epidermis, which is rather a lot like serving in a military checkpoint, instead. Because none of the cells wanted to serve in the Epidermis, there was a lot of competition, for only about thirty total cells from each hemisegment could move on to become a neural cell, and neighboring cells were never chosen.
Sometimes this made Parvani Aralyn Loky Mallen sad, for if she were chosen, she would never visit with her neighbors again. However, it took a lot to become a neural cell, so she was mostly occupied with trying to learn it all, even though she knew that this was also true if one happened to live in the correct location and wished to become any sort of specialized cell. For her part, Parvani Aralyn Loky Mallen thought that the chance to become a neural cell was a very good thing, better than most of the others. Included in the required knowledge was the action and activity of the proneural genes, which all cells hoping to become neural had to learn how to express. Among the most important of these genes were those of the achaete-scute complex, which could be used to initiate a cell’s specification into neural-cell-hood via their ability to regulate the expression of other genes (which, Parvani Aralyn Loky Mallen knew, were known as “target genes”).
Parvani Aralyn Loky Mallen also knew that the achaete-scute complex encoded DNA binding proteins, characterized by the basic helix-loop-helix domains, which formed homo- and hetero-dimers with each other, and that the selection to be a neuroblast would occur in five rounds, each in a different time and a different place. She even knew that if she were chosen, she would get a unique assignment, the nature of which depended on which hemisegment she lived in, where in it she lived, and at what time she was chosen.
Finally, the eve of the Delta-Notch test, which was used to determine who could be a neural cell, arrived. Each cell that was present began to prepare, making its Notch proteins, which, as all hopeful neural-cell-hood applicants know, are the receptors to which Delta proteins bind, over the course of the night, for when the signal to start production of Delta came, there would be no mercy. The signal came. Parvani Aralyn Loky Mallen focused inward, watching as the achaete-scute proteins bound to her DNA, activating the transcription of that all important protein: Delta.
I will be a neural cell, I will, I will, she chanted to herself, feeling the Delta proteins fold and make their way to her membrane. She felt the lurch as another cell’s Delta protein found one of her Notch proteins; saw it activate a Suppressor-of-hairless transcription factor, which in turn activated an Enhancer-of-split factor. She felt the resultant reduction in her Delta production, but she refused to stop. After all, her Delta was acting on the others, just as surely as theirs was on her.
I have more though, I know I do. The thought was almost prophetic, for in the next few moments, those around her gave out, some groaning, some simply dropping without a sound. She was startled when the announcer said that the contest was done, even more startled to realize that she was the one selected. She was now a neuroblast!
A Cell’s Take on Neuroblast Formation in Drosophila: An Overview
It goes without saying that for all major decisions, the vast majority of those deciding like to have someone else to talk things over with, to, if nothing else, offer reaffirmation that the decision reached is, in fact, the correct one. That this is true in humans can be deduced simply from a study of human behavior, but there are other deciders, and other decisions to be made.
Parvani Aralyn Loky Mallen was a most distinguished cell. He, or she, for it doesn’t really matter when one refers to cells, as they don’t care about such trivial, to them, aspects. We will call Parvani Aralyn Loky Mallen a she, for this fits the traditional classifications of mother cell and daughter cells, which have been used in biology for many long years. Now, after the manner of the well-to-do and (yet) polite individual, Parvani Aralyn Loky Mallen was on great terms with her neighbors. They spent countless periods together, talking and sharing the headlines in Signals This Period and Letters from your local HOX cluster. This latter was a very popular read, for it informed Parvani Aralyn Loky Mallen and her neighbors of where they were located, relative to the rest of the organism.
Parvani Aralyn Loky Mallen lived with her neighbors, along with many other distinguished well-to-do cells, in houses that made up thick rows (or maybe stripes would be better) along either side of a small street called Ventral Midline Way. The houses on one side of the street (where Parvani Aralyn Loky Mallen lived) were part of hemisegment A; those on the other side were part of hemisegment B. These houses, for though cells have a membrane and thus do not need houses, they much prefer to call the area wherein they stay their “house”, were part of the neurogenic zoning area, meaning that only special ectodermal cells were allowed to live there — mesoderm and endoderm cells had to find lodging elsewhere.
Now Parvani Aralyn Loky Mallen was very intelligent, she was a 3.99 student at the local college, Neurectoderm School for Potential, where she and her friends studied in the hopes of being selected to be a neuroblast, and thereby having a chance of becoming neural cells, though most of them, as is the sad fate of life, would end up serving in the Epidermis, which is rather a lot like serving in a military checkpoint, instead. Because none of the cells wanted to serve in the Epidermis, there was a lot of competition, for only about thirty total cells from each hemisegment could move on to become a neural cell, and neighboring cells were never chosen.
Sometimes this made Parvani Aralyn Loky Mallen sad, for if she were chosen, she would never visit with her neighbors again. However, it took a lot to become a neural cell, so she was mostly occupied with trying to learn it all, even though she knew that this was also true if one happened to live in the correct location and wished to become any sort of specialized cell. For her part, Parvani Aralyn Loky Mallen thought that the chance to become a neural cell was a very good thing, better than most of the others. Included in the required knowledge was the action and activity of the proneural genes, which all cells hoping to become neural had to learn how to express. Among the most important of these genes were those of the achaete-scute complex, which could be used to initiate a cell’s specification into neural-cell-hood via their ability to regulate the expression of other genes (which, Parvani Aralyn Loky Mallen knew, were known as “target genes”).
Parvani Aralyn Loky Mallen also knew that the achaete-scute complex encoded DNA binding proteins, characterized by the basic helix-loop-helix domains, which formed homo- and hetero-dimers with each other, and that the selection to be a neuroblast would occur in five rounds, each in a different time and a different place. She even knew that if she were chosen, she would get a unique assignment, the nature of which depended on which hemisegment she lived in, where in it she lived, and at what time she was chosen.
Finally, the eve of the Delta-Notch test, which was used to determine who could be a neural cell, arrived. Each cell that was present began to prepare, making its Notch proteins, which, as all hopeful neural-cell-hood applicants know, are the receptors to which Delta proteins bind, over the course of the night, for when the signal to start production of Delta came, there would be no mercy. The signal came. Parvani Aralyn Loky Mallen focused inward, watching as the achaete-scute proteins bound to her DNA, activating the transcription of that all important protein: Delta.
I will be a neural cell, I will, I will, she chanted to herself, feeling the Delta proteins fold and make their way to her membrane. She felt the lurch as another cell’s Delta protein found one of her Notch proteins; saw it activate a Suppressor-of-hairless transcription factor, which in turn activated an Enhancer-of-split factor. She felt the resultant reduction in her Delta production, but she refused to stop. After all, her Delta was acting on the others, just as surely as theirs was on her.
I have more though, I know I do. The thought was almost prophetic, for in the next few moments, those around her gave out, some groaning, some simply dropping without a sound. She was startled when the announcer said that the contest was done, even more startled to realize that she was the one selected. She was now a neuroblast!