Download Apical Ectodermal Ridge (AER)

The Developmental Fate of Cells
Marissa and Katie
Vocab
• Induction-The process in which one group of embryonic
cells influences the development of another, usually by
causing changes in gene expression.
• Fate Maps-A territorial diagram of embryonic development
that displays the future derivatives of individual cells and
tissues.
• Totipotent-Describing a cell that can give rise to all parts of
the embryo and adult, as well as extraembryonic
membranes in species that have them.
• Pattern Formation-The development of a multicellular
organism’s spatial organization, the arrangement of organs
and tissues in their characteristic places in threedimensional space.
• Apical Ectodermal Ridge (AER)-A thickened area of
ectoderm at the tip of a limb bud that promotes outgrowth
of the limb bud.
• Zone of Polarizing Activity (ZPA)-A block of mesoderm
located just under the ectoderm where the posterior side
of a limb bud is attached to the body; required for proper
pattern formation along the anterior-posterior axis of the
limb.
• Positoinal Infortmation-Molecular cues that control
pattern formation in an animal or plant embryonic
structure by indicating a cell’s location relative to the
organism’s body axes. These cues elicit a response by genes
that regulate development.
Introduction
• The fate of cells is determined by signals and
surroundings and influenced by other cells.
2 Ways to Alter Gene Expression
1. During early cleavage divisions, embryonic
cells must somehow become different
– Asymmetric Divisions
2. Once initial cell asymmetries are set up,
subsequent interactions among the
embryonic cells influence their fate
– Induction
Fate Maps
• 1920s Walther Vogt charted maps of early
Amphibian embryos and found that germ
layers created by gastrulation were traced to
the bastula, even before gastrulation
• Caenorhabditis Elegans(worm)
– Sydney Brenner, Robert Horvitz, and Jonathan
Sulston determined complete lineage.
– Figure 47.22
Changing Fate
1. Specific tissues of the older embryo are the
products of a certain “founder cell” that
contain unique factors as result of
asymmetrical divisons.
2. As development proceeds a cell’s
developmental potential becomes restricted.
Establishing Axis
• In amniotes and Mammals axis are established
after cleavage
• In nonamniotes axis are established during
oogenesis
• Figure 47.23
Totipotentcy
• In mammals, Totipotent until 16-cell stage
• In others, only totipotent when cytoplasmic
determinants are present
• Totipotency is lost as time goes on!
“Organizer”
• 1920s Hans Spemann and Hidle Mangold
– Dorsal lip of blastopore in early gastrula in the
organizer
– It initiates a chain of interactions that result in
formation of notochord, neural tube, and other
organs.
• Figure 47.24
BMP-4
• BMP-4 (bone morphogenetic protein 4) is a
growth factor.
• When it is in high concentration it signals cells
on ventral side of gastrula to travel down a
pathway to form ventral structure
• The “organizer” inactivates BMP-4 on dorsal
side with binding proteins promoting dorsal
structures.
Fate of Cells
• Inductive signals play a major role in pattern
formation
• Positional cues tell a cell where it is in respect
to the animals body.
• Axes:
– Anterior-Posterior
– Ventral-Dorsol
– Proximal-Distal
Limb Bud Organizers
• Two types
1. Apical Ectodermal Ridge (AER)
2. Zone of Polarizing Activity (ZPA)
• Both can interact with each other to
determine development.
Apical Ectodermal Ridge (AER)
• Removing AER blocks outgrowth of limbs
along the Proximal-Distal Axis
• Cells promote protein signals in fibroblast
growth factor (FGF) that promote outgrowth
Zone of Polarizing Activity (ZPA)
• Block of mesodermal tissue
• Located underneath the ectoderm where
posterior side of bud is attached to body
• Necessary for proper pattern formation along
the anterior-posterior axis
• Cells nearest ZPA = posterior structures
• Cells farthest from ZPA = anterior structures