BIOMG 1350 Notes Week 11
BIOMG 1350 Notes Week 11 BIOMG 1350
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This 6 page Class Notes was uploaded by genehan on Saturday September 3, 2016. The Class Notes belongs to BIOMG 1350 at Cornell University taught by Garcia-Garcia, M; Huffaker, T in Fall 2015. Since its upload, it has received 5 views. For similar materials see Introductory Biology: Cell and Developmental Biology in Molecular Biology and Genetics at Cornell University.
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Date Created: 09/03/16
BIOMG 1350 Professor Bretscher & GarciaGarcia Spring 2016 Week 11: Lecture 1 of 1 Wednesday, April 13, 2016 Lecture Title: Social Networking in Embryos Lecture Keywords: gene expression, cell signaling, paracrine and contactdependent signaling, Notch, Delta, morphogens, morphogenetic gradient, French Flag Model, pattern, denticles, organizer centers, sequential induction, Niewkoop organizer, prepattern, lateral inhibition, reaction diffusion ** Monday April 11, 2016 was Prelim #2 so there was no class ** 1. Signals can regulate gene expression a. Gene expression is very wide; certain types of genes can be expressed or repressed such as housekeeping genes or regulated genes b. When genes are regulated, depending on the nature of the gene, the expression of the gene could be expression of transcription factors, signaling molecules, or cytoskeletal proteins. i. Cell signaling can also cause changes in protein function such as regulation of transcription factors, signaling molecules, cytoskeletal proteins, and cell cycles. c. Cell signaling influences cell specification, cell growth, and cell behavior. 2. In short, cell signaling promotes short or long lasting differences amongst embryonic cells. a. Two main types that are predominant in early development are paracrine and contactdependent signaling. b. Two cells need to be directly right next to each other for contactdependent signaling, and the cell that is receiving the signal must have the proper receptor for the signal. c. Example – P2 determines ABp fate in C. elegans i. A single fertilized egg divides into two, an AB (anterior) and a P (posterior) cell. ii. They both divide again and result in Aba, ABp, EMS and P2. iii. They express different signals and receptors. Notch is the specific receptor that can be cleaved after binding a signal that can result in a change in the cell. Delta is the signal. iv. ABp is in direct contact with the cell expressing Delta. ABa also has Notch but is not in close proximity to the Delta signal so it does not react the same way as ABp, resulting in different cells to arise. d. With paracrine signaling, cells with the receptors for a signal that are nearby, not necessarily touching, can still receive signals. Cells without the proper receptors even near the signaling cell will not receive the signal. e. There is a threshold at which a developmental decision is made and ultimately causing a change caused by the signal. Signals that function in a concentration dependent manner are called morphogens. Morphogens are said to generate morphogenetic gradients, a graded distribution of morphogen. f. French Flag Model – If a cell receives high amounts of signal, this may result in Fate A. If a cell receives an intermediate amount, then it can take Fate B and if a cell receives very little signal, it can take Fate C. Thus, one signal can cause different fates in cells depending on thresholds. g. Example – mesoderm induction in frog – one signal, one fate i. Some signals are produced from the vegetal pole that form a gradient as the signal diffuses through the embryo. ii. When the signal reaches a certain threshold, cells that fall within that area become specified as mesoderm. h. Example – limb polarity – one signal, multiple fates i. In the zone of polarizing region, cells can secrete a signal that diffuse across the limb bud and depending on the concentration of the signal received by different cells at different distances from the signal, different digits form (digit 2, digit 3, digit 4). 3. Signals can create a pattern. a. If there are two signals, there can be more complex 2dimensional patterns due to two gradients. b. Pattern is a term used to refer to an arrangement of embryonic structures. c. The pattern is a consequence of cells becoming different during development. 4. When cell signaling is disrupted – a. Fly larva have a pattern of denticles in every segment and this pattern is altered when the signal Wingless is mutated. 5. Cell signals mediate induction. a. Organizer centers are where signals are produced to induce other cells. These signals are what allows cells to convince surrounding cells to become something else. 6. Sequential induction – a. A and B may signal each other which induces C by a signal from B on A. Then D and E are induced by a signal from C on A and B. b. Example – Niewkoop organizer i. Frog embryos at the blastula stage, cells in a certain quadrant are to become the Nieuwkkoop organizer which can express signals into surrounding cells. ii. These signals can only affect cells nearby because they have receptors and these become the Spemann organizer. Then, signals from the Spemann organizer can affect other nearby cells to induce changes. 7. Iclicker question – The drawing illustrates the result from an experiment on a chicken embryo where the blue region at the posterior side of a donor limb bud has been transplanted to the anterior part of the right limb bud of another chicken embryo. The left limb bud of the transplanted chicken embryo has been left intact to serve as a control. As indicated in the right figure, the area transplanted altered the digit pattern of the limb which received the transplant causing a mirror image duplication. Which of the following statements is true? a. The transplanted blue area was not specified as posterior when the transplantation was performed b. The blue area expresses a transcription factor that functions as a morphogens c. The blue area is an organizer center (TRUE) d. All of the above 8. Signals specify cell fate, and the secretion of these signals are regulated by a “pre pattern.” a. Cells in an embryo will acquire a state either because it has taken a decision before or it is told by another cell what to do. b. Resolving differences as equals – many cells can potentially become something, but they signal amongst each other and only one or a few will take on that identity c. Lateral inhibition (contactdependent) or reaction diffusion (paracrine signaling) d. Amplification of small differences i. If there is slight asymmetry due to an external source or random fluctuation, the asymmetry is selfamplifying. e. Lateral inhibition – A group of equivalent cells compete by inhibiting neighboring cells, and once a certain cell dominates, that one cell ends up “winning” and takes on a certain fate. i. Example – specification of sensory mother cells in Drosophilia 1. The prepattern determines groups of cells that express Delta and Notch, and only a few cells spaced at the right distance, will express the genes.
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