Transcript An Introduction to Embryonic Development

Introduction to Developmental
Biology
January 12, 2009
The following slides….
• This material is intended to show you the
level of knowledge that you will need
master for any given topic
– It is NOT what you should already know, but
you should have the background enabling you
to learn this material
• We will go over material from Gilbert and
from other sources when additional
information is needed for illustration and
clarity
An Introduction to Embryonic
Development
• Developmental processes include
– Gamete formation, fertilization
– Embryogenesis
– Metamorphosis
– Sexual maturation
– Wound healing
– Tissue, organ regeneration
– Stem cell behavior
– Many cancers
What regulates development?
• Developmental programs
– Internally programmed
– Induced
• Cell-Cell interactions
– Junctions and adhesion molecules
– Signaling through secreted factors or membranetethered molecules
• Cell-Extracellular matrix interactions
– Integrins and adhesive specializations
• Cell and tissue reorganization
– Epithelial-Mesenchymal Transformation (and/or
back)
An Example of material covered
• Epithelial/Mesenchymal Transformation
– Rearranging cells and tissues to build
structures and organs
• Epithelial Mesenchymal Interactions
– Changing the differentiated state of cells and
tissue through an exchange of signals
between adjacent tissues
Epithelial-mesenchymal Interactions
• Chapter 6, 15 Gilbert
• Progressive interactions of tissues through cell-cell interactions
mediated by:
– Direct contact
• CAMS
• Cadherins
• Junctions
• Notch/delta type interactions
– ECM
• Matrix to matrix
• Integrins
– Secreted growth factors
– Shh
– Wnt
– FGFs
– TGF-βs
– BMPs
• Specific receptors
Basal Lamina
Epithelia: Cell sheets,
tubes or cords of cells
with basal lamina and
subapical junctional
complexes
-Apical/Basal Polarity
Basal Lamina
E.D. Hay
You will need to understand the relationship between
organelle structure and cell/tissue function
Inter. Fil.
actin
Integrin binding
induces formation of a
focal adhesion
www.steve.gb.com
Focal adhesions bind actin filaments.
The focal adhesions are joined by
hemidesmosomes, which associate
with intermediate filaments
http://oregonstate.edu/instruction/bb450/lecturenoteskevin/c
ellularsignalingoutline.html
Ras and Growth Factors
Receptor tyrosine
kinase activity
You will need to learn and understand signaling
pathways
You will need to be able to learn and understand structure and function of ECM
Binds the
Integrin
Fibronectin: two 220 kDa chains, multiple binding
domains.
• You will need to apply these facts,
functions and mechanisms to
synthesize an understanding of
increasingly complex systems as the
semester goes on.
Induction and response
• There are inducing tissues that produce a signal
and
• Responding tissues that make some change in
response to the signal
• In order to respond a tissue must be competent
– State of differentiation
– Presence of receptors
• Mutual interactions can occur simultaneously
(limb, kidney) or sequentially (teeth)
Instructive vs Permissive
• If a signal from one cell/tissue is required
for the response of a target cell/tissue, that
is called an Instructive Interaction
• If a tissue has all of the factors it needs to
develop/differentiate within itself and only
needs an enviornment that allows intrinsic
processes to occur, that is called a
Permissive Interaction
Some interactions are epithelial/epithelial, some
epithelial/mesenchymal
Example of instructive interaction: epithelial/epithelial
Progressive interactions in eye development
Shows interaction between the optic vesicle and the
lens placode to induce lens formation. Then an
interaction between lens and prospective retina
affecting neural retinal development. --Mutual
interaction
• But the optic vesicle/lens placode
interaction is not the start of the inductive
cascade….
Lens induction in newts
Progressive interactions in lens induction
• Inducers have additive effect
• Order of tissues with inductive capacity:
– Pharyngeal endoderm
– Cardiac mesoderm
– Optic vesicle
• The lens epithelium must be competent to respond
-role of Pax6:
-Pax 6 expression occurs if the early inductive interactions have
occurred
-as long as the lens/surface ectoderm can express Pax 6, then the
lens can form
You will need to learn about patterning genes
Competence and lens induction: role of Pax6
Progressive interactions in eye development
Must be Pax6 positive
Feather formation: epithelial/mesenchymal between
the skin ectoderm and dermis
Classical Example of Epithelial/Mesenchymal Interaction
Feather germ formation and development
• The epidermis makes the skin appendage (feather, etc), but the type
of appendage made is determined by instructions from the dermis in
different regions of the body
• If epidermis from the wing is paired with dermis from the leg, scales
will form instead of feathers
• Studying feather and scale formation in chick in detail shows a more
complicated explanation and a potential role of the epidermis.
– Combining feather-region epidermis with 13-day chick embryo
tarsometatarsal dermis forms scales.
– However, when recombined the same epidermis with a 10-day
tarsometatarsal dermis it forms feathers.
– This means that the dermis acquires it inductive ability gradually
and the epidermis has an inherent identity that can be
overcome by competent dermis
– FGF3 and 10 are produced by the dermis in the area where a
feather will be induced
Mouse feathers
• It is possible to combine chick skin
epidermis that will form feathers with preinstructive dermis from mouse and the
mouse dermis will “go along” with the
program of the skin to make mouse
feathers (Dhouailly)
Overall Goal of K331
• We will learn about processes and mechanisms
used in the formation and development of many
tissues and organs
• We will examine the formation of embryonic
germ layers, tissues and organs, giving you a
basic foundation in Developmental Biology
– But NOT all of the organs in the body
• By studying a range of tissues and organs you
will develop the tools to study any tissue or
organ development