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BIOMG 1350 Notes Week 11

by: genehan

BIOMG 1350 Notes Week 11 BIOMG 1350


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Week 11 Notes
Introductory Biology: Cell and Developmental Biology
Garcia-Garcia, M; Huffaker, T
Class Notes
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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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