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Genetic and Cellular Mechanisms of Pattern
Formation
VII. Neighboring cells instruct other cells to form particular structures: cell
signaling and induction in the nematode
A.
Introduction
1.
Induction: recall that this is involves some sort of communication
between cells, either molecularly or by contact, to cause cellular
differentiation by activating genes.
B. Induction in Vulval Development and C. elegans
1.
C. elegans is a kind of “worm”, a nematode.
2.
The vulva, the structure through which eggs are laid, has been studied.
3.
In its larval stage, C. elegans has 6 cells in the area that will develop
into the vulva.
4.
What is called “the anchor cell” will release inducer molecules that
will cause changes in the other vulval precursor cells.
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Genetic and Cellular Mechanisms of Pattern
Formation
B. Induction in Vulval Development and C. elegans (cont’d)
5.
Receptors in the vulva precursor cells bind to the inducer.
6.
The cell closest to the anchor cell, receiving the highest amount of
inducer, divides and differentiates to form the inner part of the vulva
and also produces a second inducer.
7.
Other vulval precursor cells have receptors for this second inducer,
bind to the inducer, divide and become outer vulva cells.
8.
This cascade of induction can be found in the formation of many other
organs, in many other animals, all by signal transduction pathways.
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Figure 21.17 Cell signaling and induction in the development of the nematode vulva
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Genetic and Cellular Mechanisms of Pattern
Formation
C. Programmed Cell Death (Apoptosis)
1.
Definition: timely cell suicide during organismal development
2.
Suicide proteins are produced that cause the cells to breakdown, die
and then are engulfed by neighboring cells.
3.
Genes and Proteins Involved in C. elegans
a)
In C. elegans there are two apoptosis genes, ced-3 and ced-4,
coding for proteins Ced-3 and Ced-4. These proteins are kept in
the inactivated form in the cell (so they are stored)
b) Ced-9 regulates Ced-3 and Ced-4.
c)
These proteins all activate nucleases and proteases
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Genetic and Cellular Mechanisms of Pattern
Formation
C.
Programmed Cell Death (cont’d)
4.
Apoptosis in Humans
a)
It is thought that apoptosis proteins cause the mitochondrial
membrane to leak which releases other self-destructive proteins.
b)
One such molecule is cytochrome c which is part of the electron
transport chain.
c)
Important in:
i.
Formation of fingers and toes
ii.
Normal operation of the immune system when cells kill viral
infected cells.
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Figure 21.18 Apoptosis (programmed cell death)
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Genetic and Cellular Mechanisms of Pattern
Formation
VIII. Plant development depends on cell signaling and transcriptional regulation
A.
Introduction
1.
Cell signaling could not rely on cellular movement because of the
rigid cell walls.
2.
Plant morphogenesis or the taking of shape relies on the plane in
which a cell divides.
3.
Plants are similar to animals in relying on induction and regulating
transcription.
4.
Arabidopsis has been the main plant used for these studies.
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Genetic and Cellular Mechanisms of Pattern
Formation
B.
Cell Signaling in Flower Development
1.
Plants will develop flowers at certain times based on temperature,
length of night and so these environmental cues affect cell signaling.
2.
A floral meristem: this is a growing region of a plant that will
develop into a flower.
i.
The floral meristem has 3 layers to it.
ii.
The flower that will be produced has very different parts: petals,
egg-containing carpels, stamens which bear the anthers with
pollen and usually green sepals which cover the petals when the
flower is closed.
iii.
Researchers found that chimeras, organisms that were made of
genetically different cells, like one of the cell layers was from
one plant and another cell layer from another, had floral
development controlled by one of the cell layers (layer 3 or the
innermost)
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Figure 21.19 Induction in flower development
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Genetic and Cellular Mechanisms of Pattern
Formation
C.
Organ Identity Genes in Plants (Arabidopsis)
1.
Organ Identity Genes: these genes determine whether a petal or a
stamen or some other organ will grow.
2.
Mutations in an OIG can produce a petal where some other
structure should be located. These OIG therefore are analogous to
the homeotic genes in the fruit fly.
3.
These OIG could be controlling a whole series of other genes to
bring about the flower’s proper structure.
4.
OIGs encode for transcription factors that bind to DNA
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Figure 21.20a Organ identity genes and pattern formation in flower development: Normal flower development
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Figure 21.20b Organ identity genes and pattern formation in flower development: In situ
hybridization
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Figure 21.20c Organ identity genes and pattern formation in flower development:
Organ identity mutants
Last Lecture Slide
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Figure 21.x2a Laboratory mice: brachyury mutant
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Figure 21.x2b Laboratory mice: eye-bleb mutant
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Figure 21.x2c Laboratory mice: Hfh11 mutant
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Figure 21.x2d Laboratory mice: Lama2 mutant
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Figure 21.x2e Laboratory mice: Lepr mutant
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Figure 21.x2f1 Laboratory mice: Mgf mutant
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Figure 21.x2f2 Laboratory mice: Pax3 mutant
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Figure 21.x2g Laboratory mice: Otc mutant
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Figure 21.x2h Laboratory mice: Pax6 mutant
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Figure 21.x2i Laboratory mice: Pit1 mutant
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Figure 21.x2j Laboratory mice: pudgy mutant
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Figure 21.x2k Laboratory mice: ruby-eye mutant
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Figure 21.x2l Laboratory mice: stargazer mutant
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Figure 21.x2m1 Laboratory mice: ulnaless mutant
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Figure 21.x3 Nude mouse
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Figure 21.x4 Normal and double winged Drosophila
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Figure 21.x1 Drosophila eyes
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Figure 21.4 Cell lineage in C. elegans
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Figure 21.9 Determination and differentiation of muscle cells (Layer 1)
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Figure 21.9 Determination and differentiation of muscle cells (Layer 2)
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Figure 21.9 Determination and differentiation of muscle cells (Layer 3)
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Figure 21.x5 Mutant Drosophila eyes
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Figure 21.15 Homologous genes that affect pattern formation in a fruit fly and a
mouse
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Figure 21.16 Homeobox-containing genes as switches
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