Hungy, Hungy....HPO!!!

   Delving deeper into the understandings and workings of the feeble, yet supremely interesting specimen, Drosophila grimshawi, I have finally decided on a gene that not only has unique implications affecting itself, but may one day help us to understand other larger queries, such as how to slow, or perhaps stop cancer. The hippo (Hpo) gene is crucial in more than just one specific way. It acts as a "slippery-slope" guardsman. Its main significant function, in tandem with sav & wts, is to regulate cell growth, reproduction, and programmed cell death (apoptosis). Coordination between these three processes needs to be balanced in order to maintain homeostasis in multicellular organisms. The reason I say hpo is a guardsman is because if hpo is mutated or missing, then cell growth and reproduction continues on, unchecked. That, along with no cell death, can cause the organs to become enlarged, and mutated, and ultimately lead to the death of the organism. If a cell becomes cancerous, and there is no cell death due to no hpo, then that cell will replicate and that can be disastrous. Not on hpo's watch! In 2003, the hippo gene made its debut in multiple publications simultaneously, becoming something of interest.

     This four allele, 2800bp gene is located between 15381k and 15385k. It has 2 exons and 669 amino acids. it belongs to the Ste20 family of kinases, consisting of over 20 members, including Ste20. This family trigger the activation of mitogen-activated protein kinases (MAPK) pathways in eukaryotes. Mammalian Ste20-family kinases, MST1 and MST2 are orthologs of hpo. Hpo contains three conserved domains: an amino-terminal kinase domain, a central autoregulatory domain that inhibits kinase activity, and a domain implicated in dimerization and binding Sav at its terminus.  Now that we have a better understanding its structure, lets continue on why Drosophila need it so badly. 

     The increase in cell number that comes with the growth of an organ or organism is a result from the fickle equilibrium between the three main components; cell proliferation, cell growth, and cell death during development. How these three processes are coordinated and executed with precision is not completely known. However we do know that without hpo, or its counter-parts (Sav & Wts), it will result in increased cell proliferation and reduced apoptosis. Studies believe and have suggested that these genes function in a common pathway, known as the Hpo pathway, that coordinately regulates cell proliferation and apoptosis by targeting the cell-cycle regulator CycE and the cell death inhibitor DIAP1. Studies that have incorporated large hpo clone mutations show that the Drosophila wings were larger than the normal, wild-type wings. In retinal sections, the hpo clones revealed that mutant ommatidia (components of the eyes, containing photoreceptors) appear to have the normal complement and arrangement of photoreceptor cells. The hpo mutant ommatidia showed to have more tissue between adjacent ommatidia.  This indicates that hpo plays a role in the regulation of organ size in tissues in multiple organ systems.

     Along with helping maintain a healthy tissue size, hpo is required for cell cycle exit and regulates the expression of CycE. Cyclin E is a paramount force that is needed for cell division (G1-S phase). However, over exposure of CycE is linked to many types of cancer, or can cause abnormalities such as impaired maturation. Needless to say, regulating this member of the cyclin family is crucial to the overall well being of the organism. Hpo regulates the exposure of CycE to maintain functionality of its job, but not too much to cause adverse affects on the cell system. 

      Finally, Hpo assists in the process of apoptosis. Cell death is triggered by regulated expression of the pro-apoptotic proteins Head involution defective(Hid)), Grim & Reaper. Hpo helps regulate and oversee this process, assuring that the pro-apoptotic proteins do not get out of control. It regulates DIAP1, an apoptosis inhibitor, which if too much DIAP1 is present, then the pro-apoptotic proteins cannot reduce the DIAP1 levels enough to activate caspases in the cells. So, once again, from the shadows, Hpo works diligently to ensure that the ratio of pro-apoptotic proteins/DIAP1 stays at an appropriate level to maximize cell death. 

     With all this knowledge, it is now understood why I call this gene a "slippery-slope" guardsman. It helps maintain balance and harmony between the three important cell processes. Without it, cells would get mutated, replicate, and will not go through apoptosis, leaving a horrible abomination in place of a uniquely formed organism, if even it survives. Hpo is only one of the three musketeers of cell regulation. Along with Sav and Wts, it keeps cells the size they need to be, when they need to proliferate, and when they need to die. 

Bibliography

   -Harvey, K., Pfleger, C., & Hariharan, I. (2003, July 15). The Drosophila Mst Ortholog, hippo, Restricts Growth and Cell Proliferation and Promotes Apoptosis. Redirecting. Retrieved June 6, 2014, from http://www.sciencedirect.com/science/article/pii/S0092867403005579

   -Ejsmont, R., & Hassan, B. The Little Fly that Could: Wizardry and Artistry of Drosophila Genomics. Genes, 2014, 385-414.

   -Huang, J., Wu, S., Barrera, J., Mathews, K., & Pan, D. The Hippo Signaling Pathway Coordinately Regulates Cell Proliferation and Apoptosis by Inactivating Yorkie, the Drosophila Homolog of YAP. Cell Press, 122, 421-434. Retrieved June 5, 2014, from http://www.sciencedirect.com/science/article/pii/S0092867405005520

   -Heallen, Todd, et al. "Hippo pathway inhibits Wnt signaling to restrain cardiomyocyte proliferation and heart size." Science 332.6028 (2011): 458+. Academic OneFile. Web. 8 June 2014

   -Wu, Shian, Huang, Jianbin, Dong, Jixin, & Pan, Doujia. (2003, July 15). Hippo Encodes a Ste-20 Family Protein Kinase that Restricts Cell Proliferation and Promotes Apoptosis in Conjunction with Salvador and warts. 

Which Gene Shall Be Chosen??

     As we continue to uncover and discover the secrets of the living universe, we have to pay homage to the little organisms for paving the way; making it all the easier to "take on the world". The Drosophila are one such organisms. The genomic studies of the Drosophila alone have creative breakthroughs in understanding what genes do and their implications to other living beings.
      I am to look into one specific Drosophila gene and break it down to to its structure, function, and applications it may have on other living organisms. I have utilized the online article search from the National University online library, as well as looking at 3rd party sources, such as NCBI and sdbonline.org to find and understand the extremely long list of Drosophila genes. The main problem, however, is that I have narrowed it down to three genes that I find equally interesting and impressive, but cannot choose a single one. The genes I am looking at are the hippo(Hpo), hephaestus(heph), and Adh transcription factor 1(Adf1) genes. One deals with cell restriction and apoptosis. Another is a protein that is helpful for wing development. Last one is involved in neuronal differentiation and function.
 

   The first gene, hpo, located in the nucleus and cytoplasm of the cell, works with other genes (salvador, warts) to restrict cell growth and promotes cell death by decreasing the level of an ubiquitin ligase, which functions as an inhibitor of apoptosis. Restricting cell growth is monumentally important in ensuring that the final size of each organ is appropriate to the specific animal. The balance between proliferation and cell death is crucial and needs to be controlled and coordinated by developmental cues so that the animal's body parts reach the right size and shape. Without the hpo gene, and ones like it, cell proliferation will get out of control and reduce the rate of apoptosis. That would lead to an increase in organ size, which can cause severe problems in the organism.
   

     Secondly, there is the heph gene, which is responsible for attenuating Notch activity after ligand-dependent activation during wing development. Notch is a transmembrane receptor that is responsible for lateral inhibition and cell fate choices. The first heph alleles was identified in a genetic screen for loci required for spermatogenesis. Other heph alleles have been found that affect wing margin and wing vein pattern formation. This gene encodes the apparent homolog of mammalian polypyrimidine tract binding protein (PTB), which acts a transcriptional activator, controls alternative exon selections, translational control or internal ribosome entry site use, and mRNA stability and localization. Studies have shown that cloned organisms that lack the heph gene tend to be wingless or have cut wings, induced ectopic wing margin, inhibit wing-vein formation and have increased Notch activity. This shows that though it does not seem detrimental to the survival of the organism, it in fact is key to the correct development of the characteristic that is described in its name, the fruit FLY.
 

   Lastly, there is the Adh transcription factor 1 (Adf1). It was first identified as a factor that bound the distal promoter of the gene for alcohol dehydrogenase. It is involved in terminal stages of neuronal differentiation and function. The Adf-1 reveals that its DNA-binding is a distantly related member of the helix-turn-helix family, though reavels no similarities to known transcriptional activation domains. This means that it may function through a novel transactivation domain, such as nalyot, a olfactory memory mutant. Studies have shown that Adf-1 mutants have normal memory starting out, but their long-term memory is affected. Adf-1 shows widespread spatiotemporal expression, yet mutant allele show no noticeable complications in morphology of the nervous system. Studies also show that Adf-1 plays a major role in the modulation of synaptic growth. That is a lot of scientific jargon, but even if someone who isn't up-to-date with the most recent genomic language reads this, they will understand that this sequence is very important in the neural functions of the Drosophila species.
      As I mentioned earlier, each of these three sequences are complex and essential, not to mention very interesting. I have barely scratched the surface with any one of these choices, but they all have my undivided attention and I am diving into more and more of each one. Even though I can choose only one for my research, I have a feeling I will be keeping a keen eye on all the different genes that help show how and why what we see, is. Which one to choose?
     

Black Sheep of the Drosophila Family

     Understanding genetics and the animal genome is the ongoing journey to understand all of this world's living organisms, and to understand their capacity to grow and change. A certain organism has become a key component to facilitate this process; the fruit fly. 

     Under the family of Drosophilinae, the fruit fly has many excellent qualities that makes it an ideal specimen. It is easy and inexpensive to culture in a lab, has a short generation time, and has a high production of offspring, which can be modified, genetically, from the laid embryos. This makes it an efficient subject to study. Using Drosophila, scientists have a better understanding the role genes play in the development of a single cell embryo into a multi-cellular organism, not just for a fruit fly, but for all animals, including humans. Even though it is obviously clear that humans differ greatly from Drosophila, many of the underlying genetic foundations have been conserved through evolution and are very similar.  For well over 100 years, the fruit fly has been a successful tool in discovering monumental genetic information, including genetics and inheritance, learning behavior, and aging. A great deal of our understanding of biological concepts, example being tissue regeneration, comes from experiments using model specimens, such as the Drosophila. 

Drosophila grimshawi

12 sequenced Drosophila 

      There are hundreds of species of Drosophila, and, as shown above, each species differs from the others with distinct attributes. One however, the largest of the sequenced species is the most more unlike the others. 

     Drosophila grimshawi, more commonly known as the Hawaiian Fruit Fly is more diverse than any of its cousins. From the picture above, you can see the physiological differences from the other species, such as its larger size and its uniquely patterned wings. It also has a more noticeable pattern on its thorax and abdomen than can be seen from the other eleven sequenced species. This specific species of Drosophila occupies mainly five of the Hawaiian Islands (Kauai, Oahu, Molokai, Maui, and Lanai). It prefers the mountainous rain forests and has a taste for bananas and mushrooms. However, its looks and food preferences are not what makes this little bug most interesting.

     Studies have found a bizarre key detail about D. grimshawi that proves most intriguing; there is not any speciation, with very little genetic differentiation. This particular species maintains its morphology throughout the five islands where it can be easily found. What makes this so interesting is that it goes against the norm of the other Hawaiian flies. This makes D. grimshawi an anomaly. Anomalies need to be researched, and solved.