An Interactive Introduction to Organismal and Molecular Biology, 2021

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Turning Genes on in Specific Body Parts PROTEIN SYNTHESIS I: TRANSCRIPTION | 147 Some genes need to be expressed in more than one body part or type of cell. For instance, suppose a gene needed to be turned on in your spine, skull, and fingertips, but not in the rest of your body. How can transcription factors make this pattern happen? A gene with this type of pattern may have several enhancers (far-away clusters of binding sites for activators) or silencers (the same thing, but for repressors). Each enhancer or silencer may activate or repress the gene in a certain cell type or body part, binding transcription factors that are made in that part of the body. 1,2
148 | PROTEIN SYNTHESIS I: TRANSCRIPTION Example: Modular Mouse As an example, let’s consider a gene found in mice, called Tbx4. This gene is important for the development of many different parts of the mouse body, including the blood vessels and hind legs. 3 During development, several well-defined enhancers drive Tbx4 expression in different parts of the mouse embryo. The diagram below shows some of the Tbx4 enhancers, each labeled with the body part where it produces expression. Not drawn fully to scale. This Image is based on Figure 5 of Menke et al. 3 Evolution of Development Enhancers like those of the Tbx4 gene are called tissue-specific enhancers: they control a gene’s expression in a certain part of the body. Mutations of tissue-specific enhancers and silencers may play a key role in the evolution of body form. 4 How could that work? Suppose that a mutation, or change in DNA, happened in the coding sequence of the Tbx4 gene. The mutation would inactivate the gene everywhere in the body and a mouse without a normal copy would likely die. However, a mutation in an enhancer might just change the expression pattern a bit, leading to a new feature (e.g., a shorter leg) without killing the mouse. Transcription Factors and Cellular “Logic” Can cells do logic? Not in the same way as your amazing brain. However, cells can detect information and combine it to determine the correct response—in much the same way that your calculator detects pushed buttons and outputs an answer. We can see an example of this “molecular logic” when we consider how transcription factors regulate genes. Many genes are controlled by several different transcription factors, with a specific combination needed to turn the gene on; this is particularly true in eukaryotes and is sometimes called combinatorial regulation. 5,6 For instance, a gene may be expressed only if activators A and B are present, and if repressor C is absent.
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An Interactive Introduction to Orga
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An Interactive Introduction to Orga
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3. Information Communication Andrea
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10. Species Interactions Andrea Bie
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16. Protein Synthesis Overview Andr
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INTRODUCTION Andrea Bierema This
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UNIT I INTRODUCTION TO SCIENCE
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6 | NATURE OF SCIENCE Exercise Befo
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8 | NATURE OF SCIENCE At first, the
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2. SCIENTIFIC CONTROVERSIES Andrea
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5. BIBLIOGRAPHIES Andrea Bierema an
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44 | BIBLIOGRAPHIES Take this quiz
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6. INTRODUCTION TO ECOLOGY Andrea B
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7. BIODIVERSITY Andrea Bierema Figu
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BIODIVERSITY | 53 An interactive or
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BIODIVERSITY | 55 here: https://ope
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BIODIVERSITY | 57 “Feeding platyp
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SYSTEMS THINKING AND THE CARBON CYC
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CLIMATE CHANGE | 79 compared to the
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10. SPECIES INTERACTIONS Andrea Bie
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SPECIES INTERACTIONS | 83 Exercise
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• Species Interaction Web © Andr
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