Assalam-u-alaikum
I thought I should share this. High school biology is piece of cake compared to university biology. I mean I ended up getting straight A s in biology in high school by sleeping only 4-5 hours a day. This gave me a competitive edge over others since I managed to finish a lot and learn a lot compared to another. That's when I developed this passion for biology. But seriously, to survive in the university I had to change my tactics completely. I couldn't just sleep 4-5 hours b/c I had to travel total of 4 hours while commuting between the university and home. Anyways. I managed to make drastic changes to my daily habits in order to do well in the university. I ended up working with Dr. Ellen Larsen on an experiment where we tried to did some genetic crosses on fruit flies in order to study the plastic nature of the segmentation genes. It was just fun. Too bad. My experimental stocks got infested by mites and I had to terminate them before they ended.
If you want to read, here is my draft report. I will not be posting my experimental design here because that material is confidential
Also, Ellie's comments are italicized.
Creating a Designer Fruit Fly—Introducing a 15th non-head segment into Drosophila Melanogaster
Draft written by: Arzoo Zaheer
Presented to: Dr. Larsen
Course: Volunteer Research Project
Note: This is just a draft and not a final copy. I haven't put all the reference in yet.
Introduction:
In Drosophila melanogaster, mesodermal thickening and ectodermal furrows divide the embryo into parasegments (Chapter9). These parasegments are used as a guide to separate the embryo into segments and thus generate the adult fly. An adult fruit fly has 15 body segments which are established from 14 metameric divisions (parasegments) along the anterior-posterior axis (Chapter 9). The parasegments do not become the segments; rather a parasegment includes the posterior part of an anterior segment and the anterior portion of the segment behind it (Lawrence, 1992).
Determination of the Anterior-Posterior (A/P) Axis:
The body plan along the A/P axis is determined by a cascade of regulatory events which involve the maternal effect genes, the gap genes, the pair rule genes (eve and ftz), the segment polarity gene (wg, en) etc. (Lawrence 1992). The maternal affect genes, expressed in the ovaries, are responsible for the initial activation of zygotic genes such as bicoid, hunchback, nanos and caudal. These maternal factors cause cytoplasmic polarity and eventually create Hunchback protein gradient. This gradient differentially activates the gap genes and thus the process of segmentation begins. Gap genes, the first class of segmentation genes in turn activate the pair-rule genes which belong to the second class of segmentation genes (Chapter 9). For instance, Reinitz and Sharp used the gene circuit method to show that eve is activated by bicoid and other general transcription factors. They also showed that local repression of eve by other gap genes causes the formation of the stripes. (Reinitz and Sharp, 1995)
The proper activation of pair rule genes depends on combinatorial regulation by various maternal affect genes and gap gene products. Seven stripes of pair-rule gene even-skipped (eve) are seen during the mid-and late-mitotic cycle 14--the first mitotic cycle after cellularization of the syncytial blastoderm (Chan, 2001). The eve promoter constitutes of a series of enhancers which direct the expression of the 7 eve stripes segmentation stripes in the fruit fly. Kind of studies?Studies have revealed that these enhancers work properly only if they are separated by a minimum distance (Small et al, 1993). Seven other stripes made by pair-rule gene fushi tarazu (ftz) alternate with the seven eve stripes creating 14 discrete, metameric divisions called parasegments from which adult segments are derived (Chan,2001). Genetic studies have revealed that the borders of the eve and the ftz stripes are formed by the repression, not activation, of certain genes. For instances, the gap gene giant (gt) is involved in a repression mechanism which situates the anterior border of eve stripe 2 (Andrioli et al, 2002).
By the start of gastrulation, the cells located at the anterior border of eve and ftz stripes express the segment polarity gene engrailed (en). Engrailed is localized during mitotic cycle 14 which occurs about 2-4 hours after egg laying (Chan, 2001). Within each en stripe, the en-expressing cells activate transcription of hedgehog (hh) gene. The hedgehog protein binds to the hh-receptor found on the cells immediately anterior to en-expression cells. This binding activates a pathway which leads to the expression of wingless (wg) gene in the cells anterior to each en stripe and between the ftz and eve stripes. Wingless protein then activates engrailed gene. Thus a reciprocal loop is established where the en-expressing cells secrete hh, which preserves the expression of the wg in the neighbouring cells, while the wg secreting cells uphold the expression of the en and hh genes in the neighbouring cells (Chapter 9). The en domain delineates the anterior section of a parasegment while the wg domain defines the posterior section of a parasegment (Chan, 2001). Such an interface b/w en and wg at the anterior and posterior parasegments is necessary for proper segmentation (Chapter 9).
After the boundaries of the segments are formed via the Wingless/Hedgehog signalling pathway, the homeotic genes are now activated. These genes specify the structure of each segment.
The expression of the 15 parasegments in Drosophila melanogaster depends upon a highly complex and intricate interactions between a number of genes. Speculations have been raised regarding the plasticity of expression of these segments. How would the genetic machinery respond to an increased number of parasegments?
Cell Cycle:
Cell division allows multicellular individuals to grow and develop from a cell and also functions to renew, repair and replace cells in a fully grown individual (Campbell et al, 1999). A eukaryotic cell division cycle can be subdivided into four different phases—Gap1 (G1), Synthesis (S), Gap 2 (G 2) and Mitosis (M). The timing and rate of cell division in different parts of the living being contributes crucially to its proper growth, development and maintenance (Campbell et al, 1999). The sequential events in a cell cycle are regulated by cell-cycle control system. A set of molecules trigger and manage key events of cell division. The cell cycle is tightly regulated at the cell cycle checkpoints by regulatory molecules such as cyclin-dependent serine/threonine kinases (Cdks) and cyclins (Jones et al, 2000). Studies have revealed that zygotic Drosophila melanogaster CycE (DMCycE) gene produces CycE that is required for the G1 to S transition in the fruit fly embryos. DMCycE must complex with Cdk-2 to cause this transition (Jackman et al, 2002). The DMCycE is regulated by both trans-regulatory and cis-regulatory sequences which are tissue and stage specific (Jones et al, 2000). Drosophila melanogaster embryogenesis is divided up into three stages: a three hour period of 13 synchronous mitotic cycles while the embryo is a syncytial blastoderm (Li et al, 1999). This is followed by three cell divisions (14-16) during which the cellular blastoderm undergoes cell differentiation (Li et al, 1999). Mitotic cycle 14-16 lack a detectable G1 phase (Jones et al, 2000). Cycle 17 epidermal thoracic patch cells are the first embryonic cells which exhibit a G1 phase (Jones et al, 2000). Down regulation of DMCycE during cell cycle 16 is essential for cycle 17 G1 arrest in the epidermal cells before embryogenesis occur (Jones et al, 2000). About 1 hour after the 14th interphase has begun, 25 mitotic domains separate the cellular blastoderm into a fine-scale pattern. This partitioning is an early expression of differing cell fates (Joe, Year unknown).
What about the problem of extra cells being evicted from the ectoderm? The paper from Henry Krause’s lab would make your H99 stuff more understandable?
Experiment part is cut out.
Copyrighted: Arzoo Zaheer
brothers and sisters,
laying: 
