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Discussion 2 Synopsis

Discussion 2 Synopsis - Discussion 2 Synopsis Shamra Byrne...

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Discussion 2 Synopsis 09/06/10 Shamra Byrne, Katherine Avanesyan, Brittany Eldridge, Michael Savage, Bmp4 and Morphological Variation of Beaks in Darwin’s Finches In the article written by Arhat Abzhanov et al the main growth factor looked at by the authors is Bmp4. Bmp4 stands for bone morphogenetic protein 4. From the name it is clear to see that this protein plays an important role in the onset of bone formation. The authors of this paper searched for growth factors (or molecules that stimulate cell growth, cell proliferation and cell differentiation) in the mesenchyme that correlated with an increase in beak depth and width. They utilized in situ hybridization, which allows for the tracking of different molecules using tagged complimentary DNA/RNA strands, and looked at sonic hedgehog (Shh) and Fgf8 before deciding to focus on Bmp4. They chose to use Bmp4 in their experiments because it is correlated with deep and broad beak morphology. Before they started tinkering with the expression levels of Bmp4 during development they discovered that naturally Bmp4 is first activated at stage 26 in development and that elevated levels of Bmp4 are found at stage 29 in the mesenchyme. From their observations that deduced that earlier onset and higher levels of Bmp4 caused deeper and broader beak morphology. The authors of this paper looked at three different groups of finches. The first group contained G. difficilis and had sharp, small, symmetrical beaks. The second group was characterized by broad, deep beaks used for crushing seeds and includes the species G. fuliginods, G. fortis, G. magnirostris . The third group was characterized by long pointed beaks used for reaching into cactus flowers and included the species G. scandens, G. conirostris . The authors thought it was necessary to look at three different morphologies of birds in order to control the species specific differences. The researchers wanted to know whether the observed change in Bmp4 expression could be responsible for differences in beak morphology to test their theory, genes were misexpressed during development, thus testing the effects of increased Bmp4 levels. A replication-competent retroviral vector was used used to misexpress Bmp4 genes in embryonic chick tissues in ovo. The RCAS vector was chosen because they do not spread across basement membranes. This gives the ability to confine misexpression to either the facial ectoderm or
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mesenchyme. The first experiment conducted was to infect the facial ectoderm with the RCAS::Bmp4 virus. During normal craniofacial development, Bmp4 is first expressed in the epithelium of the maxillary and lateral frontonasal prominences. It turned out that infection of the facial ectoderm with the RCAS::Bmp4 virus caused smaller and narrower upper beaks. In addition, the beaks also showed a dramatic loss of chondrogenesis, the formation of cartilage in the adjacent mesenchyme. Since the vector cannot cross into the mesenchyme from the
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Discussion 2 Synopsis - Discussion 2 Synopsis Shamra Byrne...

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