Concept
statements |
Emphasis
in
your teaching
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General
importance
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1.The
generation of distinct cell types requires the generation
of molecular and cellular asymmetries.
A single cell can be asymmetric or polarized.
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2.
Cytoplasmic asymmetries can be in the form of differentially
distributed RNAs or proteins, and usually both.
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3.
Cytoplasmic asymmetries lead to differential patterns of
gene expression in the cells that come to reside in different
regions of the embryo.
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4.
In some species, where sperm enter
the egg is predetermined. In other species, the site of
sperm entry serve to establish
asymmetry.
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5.
Asymmetries can be generated by the relative positions
of cells within an embryo; surface cells can differ from
internal cells.
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6. Differential
gene expression in turn leads to altered
cytoplasmic and nuclear composition. It is this process
that generates differentiated cells; cells with distinct
morphologies and functions within the organism.
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7.
Changes in chromatin organization occur
during the process of differentiation can are involved
in the stability of the differentiated state. These are
an example of epigenetic changes.
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8.
Cellular asymmetries can lead to asymmetries in intercellular
interactions, which in turn can stabilize or direct further
cellular asymmetries.
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9.
Inductive interactions between cells can involve juxtacrine (direct
contact, surface-mediated), paracrine (short
range secreted factor-mediated) and endocrine (long
range secreted factor-mediated) signaling events between
cells.
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10.
Often interactions between groups of cells are required
in order to respond to an inductive signal. Rarely do individual
cells differentiate independently of their neighbors, rather
groups of cells differentiate to form a tissue. This is
known as the community effect.
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11.
Cells can respond differently to differences in level of
inductive signals. This behavior underlies morphogenic/inductive
gradients. These gradients can lead to
new cell types and new inductive signals.
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12.
The regulated movement of cells and changes in cellular
morphology are critical to both the patterning of inductive
interactions and the process of morphogenesis during
development and organ formation.
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13.
The timing of inductive events is critical to normal developmental
events.
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| 14. Inductive
signaling is mediated by secreted
factors and cell
surface ligands, membrane
and intracellular receptors and the intracellular signal
transduction pathways that they regulate.
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| 15.For
each positively acting factor there are generally antagonists and co-factors that
modulate 'signal strength' and specificity. |
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| 16. Signal
transduction pathways often regulate gene
expression by regulating
the activity of transcription factors. Signal transduction
pathway can also regulate protein activity
involved in cell
morphology,
movement,
division or survival. |
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| 17. It
can be assumed that a number of inductive events
underlie each aspect of embryonic development. These are
not necessarily additive; they can involve complex
and non-linear interactions. |
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| 18. The
formation of organs, and the tissues that compose them, is
based on a similar process of inductive interactions. |
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