Transcript 2.E.1 Development

2.E.1 timing and coordination
Read Chapter 18.2-18.4
Watch bozeman science video
“timing and coordination”
Timing and coordination of specific events
are necessary for the normal development
of an organism, and these events are
regulated by a variety of mechanisms.
Draw 6 boxes on your paper
The determination of different cell types (cell
fates) precedes differentiation and involves the
expression of genes for tissue-specific proteins.
Tissue-specific proteins enable differentiated
cells to carry out specific tasks.
Cell differentiation follows determination as
the cell continues on a specific developmental
path. Differentiation results in cell types such as
nerve cells, blood cells, and muscle cells.
http://biology.kenyon.edu/courses/biol114/Chap11/Chapter_11.html
A single-celled zygote can develop into a
multicellular adult organism that contains
hundreds of different cell types.
Totipotent cells are stem cells that can
form all the cell types in a body, plus
placental cells. Embryonic cells within the
first couple of cell divisions after
fertilization are the only cells that are
totipotent.
Pluripotent cells can give rise to all of
the cell types that make up the body;
embryonic stem cells are considered
pluripotent.
The transformation from a zygote into an
organism results from three interrelated
processes:
• Cell division: the zygote gives rise to a large number
of cells through a succession of mitotic cell divisions
• Cell differentiation: cells become specialized in
structure and function
• Morphogenesis: the processes that give shape to
the organism and its various parts
Box #1
• Compare cell differentiation and cell division.
Genomic Equivalence: Nearly all the cells of an
organism have the same genome. Cells
differentiate through differential gene
expression.
Observable cell differentiation results
from the expression of genes for
tissue-specific proteins.
Hierarchy of Gene Activity in Early Drosophila Development
Maternal effect genes (egg-polarity genes)
Gap genes
Pair-rule genes
Segment polarity genes
Homeotic genes of the embryo
Other genes of the embryo
Segmentation genes
of the embryo
Box #2
• Describe the function of tissue specific
proteins.
Regulation of transcription factors during
development results in sequential gene expression.
Transcription factors are proteins that bind to
specific DNA sequences, thereby controlling the flow
of genetic information from DNA to mRNA.
Cell signaling helps direct daughter cells
down the appropriate pathways, a process
called induction. Cells induce neighboring
cells to differentiate.
2
Anterior
Posterior
1
4
3
Receptor
EMBRYO
4
3
Signal
Anterior
daughter
cell of 3
Will go on to
form muscle
and gonads
Posterior
daughter
cell of 3
Will go on to
form adult
intestine
Signal
protein
During induction, signal molecules from
embryonic cells cause transcriptional
changes in nearby target cells.
Early embryo
(32 cells)
NUCLEUS
Signal
transduction
pathway
Signal
receptor
Signal
molecule
(inducer)
An inducing signal produced by one cell in
the embryo can initiate a chain of
inductions that results in the formation of
a particular organ.
Homeotic genes are involved in
developmental patterns and sequences.
Box #3
• Describe how induction can lead to the
development of an organism.
Hox genes are a group of
related homeotic genes that control
the body plan of the embryo.
Pattern formation in animals and plants results
from similar genetic and cellular mechanisms.
Pattern formation is the development of a
spatial organization of tissues and organs.
• Occurs continually in plants
• Is mostly limited to embryos and juveniles in
animals
An identical or
very similar
nucleotide
sequence has
been discovered
in the homeotic
genes of both
vertebrates and
invertebrates.
Adult
fruit fly
Fruit fly embryo
(10 hours)
Fly
chromosome
Mouse
chromosomes
Mouse embryo
(12 days)
Adult mouse
Embryonic induction in development
results in the correct timing of events.
Box # 4
• Describe the function of homeotic genes
Temperature and the availability of water
determine seed germination in most
plants.
Genetic mutations can result in
abnormal development.
Snake with
one limb.
Box # 5
• Describe environmental and mutations effect
on development
Genetic transplantation experiments
support the link between gene expression
and normal development.
In nuclear transplantation, the nucleus of
an unfertilized egg cell or zygote is replaced
with the nucleus of a differentiated cell.
Experiments with frog embryos have shown that a
transplanted nucleus can often support normal
development of the egg.
Frog embryo
Frog egg cell
Fully differentiated
(intestinal) cell
Less differentiated cell
Donor
nucleus
transplanted
Most develop
into tadpoles
Frog tadpole
Enucleated
egg cell
Donor
nucleus
transplanted
<2% develop
into tadpoles
In 1997, Scottish researchers cloned a lamb
from an adult sheep by nuclear
transplantation.
Reproductive Cloning
“Copy Cat” was the first cat ever cloned.
In most nuclear transplantation studies, few cloned
embryos develop normally.
Genetic regulation by microRNAs plays an
important role in the development of
organisms and the control of cellular
functions.
MicroRNA (miRNA) are a small, non-coding
RNA molecules that function in posttranscriptional regulation of gene expression.
They generally bind to their target mRNAs and
repress protein synthesis by destabilizing the
mRNA.
Programmed cell death (apoptosis) plays a role
in the normal development and differentiation.
Cell signaling is involved in programmed cell
death.
Apoptosis plays a critical role in the sculpting of
digits in vertebrate limbs. The death of the
cells that would otherwise form inter‐digital
webbing enables individual fingers and toes to
be formed.
Example: Morphogenesis of fingers and toes
Time after fertilization (hours)
As early as the four-cell stage in
C. elegans, cell signaling helps
direct daughter cells down the
appropriate pathways. Induction
is also critical later in nematode
development as the embryo
passes through three larval
stages prior to becoming an
adult. A protein in the outer
mitochondrial membrane serves
as a master regulator of
apoptosis .
Zygote
0
Nervous
system,
outer
skin, musculature
10
First cell division
Germ line
(future
gametes)
Musculature
Outer skin,
nervous system
Musculature,
gonads
Hatching
Intestine
Intestine
Eggs
ANTERIOR
Vulva
1.2 mm
POSTERIOR
Example: Development in the nematode
C. elegans
Floral meristems contain three
cell types that affect flower
development.
Stamen
Carpel
Petal
Cell
layers
L1
L2
L3
Sepal
Floral meristem
Tomato flower
Example: Flower development
Box #6
• How does apoptosis aid in development?
Learning Objectives:
LO 2.31 The student can connect concepts in and across domains to
show that timing and coordination of specific events are necessary
for normal development in an organism and that these events are
regulated by multiple mechanisms. [See SP 7.2]
LO 2.32 The student is able to use a graph or diagram to analyze
situations or solve problems (quantitatively or qualitatively) that
involve timing and coordination of events necessary for normal
development in an organism. [See SP 1.4]
LO 2.33 The student is able to justify scientific claims with scientific
evidence to show that timing and coordination of several events are
necessary for normal development in an organism and that these
events are regulated by multiple mechanisms. [See SP 6.1]
LO 2.34 The student is able to describe the role of programmed cell
death in development and differentiation, the reuse of molecules,
and the maintenance of dynamic homeostasis. [See SP 7.1]