Developmental Bio Flashcards
What are the four main ways in which cells differ post differentiation?
Proliferation
Specialization
Communication
Migration
Describe altering potency of cells early in development.
Prior to the morula stage they are totipotent, and afterwards begin to become pluripotent.
What is the first evidence of differentiation within the embryo?
Differentiation of the embryo into the outer trophoblast (will form extraembryonic tissues such as chorion and placenta) and inner embryoblast.
Describe generally how cells initiate differentiation.
Inductor cells secrete morphogens that act on component cells/tissue to spur differentiation.
Describe a developmental field.
An area of cooperating cell groups, each of which takes on a unique fate in order for development to occur properly.
What are the types of options a cell faces during differentiation?
Binary options and complex options.
How are binary developmental decisions often made?
Without stimulation from a new growth factor or morphogen above a threshold level, default pathway will be followed, which is continuation down the pathway assigned by an earlier morphogen. A new morphogen can cause new downstream signals, spurring the cell to follow a different differentiation pathway(ex. SRY protein presence).
How are complex developmental decisions typically made?
A gradient is established, for which varying levels of the morphogen confer different developmental pathways, not just one or another.
Intracellular gradient- Causes an asymmetric division of a parent cell into different daughter cells.
Extra cellular gradient- Morphogen level causes different developmental pathways depending on level of morphogen the cell is exposed to on a spectrum.
Describe HOX genes.
Are the master switch TFs, due to expression regulation of many downstream genes that affect downstream morphogenesis.
Describe how HOX genes are affected by vitamin A levels.
Too little: Malformations in eyes, genitourinary tract, cardiovascular system, and lungs.
Too much: Malformations of CNS, cardiac, and craniofacial areas.
Describe PAX genes.
Are similar TFs to HOX genes, except they function singly rather than in concert.
Describe type 1 and 2 Waardenburg syndrome.
AD loss of function mutations of PAX 3 cause deficiencies of many neural crest cells. Phenotype is white forelock, deafness, pale eyes, and upper limb defects.
Type 2 affects MITF only, which is one of the proteins affected by Pax3, leading to only white forelock and deafness.
What are the other classes of early TFs expressed?
SOX- SRY gene TFs
TBX- Activator and repressor TFs involved in mesoderm and notochord differentiation.
Zn-finger genes- TFs containing this DNA binding domain.
Describe Sonic Hedgehog, and how its pathway is activated.
It is a master signal morphogen that associates with cholesterol, binds/inactivates Patched receptor, ultimately allowing Smoothened to activate the SHH pathway.
Describe limb formation.
- At 28 days of development, limb buds begin to become visible.
- At the limb tip is the apical ectodermal ridge, in which cells secrete FGF to maintain limb outgrowth.
- HOX genes expressed in progress zone (between AER and mesodermal core) determine limb type (fore or hind).
- SHH is expressed from the zone of polarizing activity at the posterior portion of the limb bud, establishing anterior/posterior differentiation of the limb.
- Combination of SHH and FGF gradients affect type of HOX gene expressed in progress zone regions. As outgrowth occurs at distal end of progress zone, areas further from AER begin to differentiate to cartilage and muscle.
- At 42 days of development, distal and proximal limb sections are separated via the circular constriction, which leads to limb ends flattening into hand and foot plates.
