Transcript Gallup47 - MsLsAPbiology4everyone

Chapter 47
Animal Development
Nicole Gallup
Embryonic Development
• Genomes of zygote and differences btwn early embryonic
cells determine development
• Cytoplasmic Determinants – Uneven distribution of
maternal substances in the unfertilized egg
• Differences between cells because of their location in the
embryo
• Cell Differentiation – specialization of cells form and
function, caused by gene expression
• Morphogenesis – process by which an embryo takes shape
and cells are in the appropriate locations
Embryonic Stages
• Fertilization – When Gametes (sperm and egg) unite
• Cleavage – Rapid Cell divisions after Fertilization. S phase
(DNA synthesis) and M phase (mitosis). Skips protein synthesis
• Gastrulation – Morphogenetic phase  Drastic
rearrangement of the cells of the blastula. Forms a threelayered embryo with a primitive gut.
• Organogenesis – When regions of the three-layered embryo
develop into fundamental organs
Fertilization Vocab
• Acrosomal Reaction - discharge of a sperm’s acrosome when
it is near the egg
• Acrosome – Vesicle at the tip of sperm, helps sperm
penetrate the egg
• Fast Block to Polyspermy – Depolarization of egg membrane
after sperm binds to vitelline layer. Prevents more sperm from
entering
• Fertilization Envelope - the changed vitelline layer – prevents
other sperm from entering the egg
• Slow Block to Polyspermy – Formation of fertilization
envelope and other changes, opposite of Fast block, lasts
longer
Fertilization
• Fertilize externally – eggs and sperm are released at the same time.
• Sperm touches egg’s jelly coat – triggering release of acrosome –
hole is formed in jelly
• Acrosomal process forms – protrudes from sperm, penetrates jelly
coat, binds to receptors on egg cell – aka acrosomal reaction
• Hole made in vitelline layer – allows contact and fusion of gamete
plasma membranes – membranes depolarize forming Fast block
• Sperm nucleus enters cytoplasm of egg – then slow block forms
Cleavage Vocab
• Blastomer – smaller cells that the embryo divides into
• Morula – cluster of cells after the first 5-7 divisions
• Blastocoel – a fluid filled cavity
• Blastula – hollow ball of cells
• Yolk – stored nutrients – distributed differently in all embryos
• Vegetal Pole – The pole that the yolk is most concentrated
• Animal Pole – Opposite pole, very little yolk
Cleavage
• After fusion of gametes cytoplasm rearranges forming 1 body
axis. Other axes form later
• First 2 divisions are meridional (Vertical) = 4 blastomers of
equal size
• Third division is equatorial (Horizontal) = 8 blastomers of
unequal size – Animal hemisphere = small cells, Vegetal
hemisphere = lager cells
• Blastula is located in the Animal Hemisphere
Gastrulation Vocab
• Gastrula – 3 layered Embryo
• Germ Layers – The 3 layers produced.
• Ectoderm – Outer layer
• Endoderm – Inner Layer
• Mesoderm – Partly fills space between Ecto and Endo
• Invagination – When cells fold inward
• Archenteron – Primitive Gut
• Blastopore – Opening in the archenteron, develops into the
anus.
Gastrulation
• Complicated mechanics – Large amount of yolk & blastula is
more than 1 cell thick
• Begins on back side of Blastula – cells begin to invaginate in
the line along the region
• Dorsal Lip – The Dorsal side of the blastopore
• Lip extends and invagination continues until the two ends on
the blastopore meet on the ventral side
• Involution – When future endoderm and mesoderm cells on
the surface roll over edge of the lip into the interior of the
embryo
Gastrulation
• Inside – cells move away from blastopore and become germ
layers and blastocoel collapses
• Yolk Plug – Large food-laden endodermal cells surrounded by
blastopore
• End of Gastrulation, circular lip of blastopore encircles plug,
cells on surface becomes the ectoderm
• Anus forms from the blastopore and mouth develops at the
opposite end.
Organogenesis Vocab
• Notochord – Formed from dorsal mesoderm
• Neural Tube – when neural plate curves inward – rolling into
itself
• Neural Crest – band of cells along border of Neural tube
• Somites – Paired blocks of mesoderm lateral to notochord
Organogenesis
• First organs to take shape – neural tube and notochord
• Signals from notochord to ectoderm cause ectoderm to
become neural plate
• Cells from neural crest migrate to all parts of the body – form
peripheral nerves, teeth, skull bones
• Some somites become wandering cells – go to new locations.
• Organogenesis continues – cell differentiation continues to
refine organs
Neural Plate
formation
Neural Tube
Formation
Somites
Morphogenesis
• Major aspect of development in animals – involves movement
of cells.
• Changes in shape involve reorganization of the cytoskeleton.
Cytoskeleton drives cell migration.
• Cells that move 1st drag others behind them – directs
movement of a sheet if cells
• Convergent Extension – morphogenetic movement – cells of
tissue layer rearrange, sheets become narrow (converge) and
become longer (extend)
Extracellular Matrix
• Extracellular Matrix (ECM) – Mixture of secreted glycoproteins
outside plasma membrane of cells – trigger/guide movement
• Some ECMs promote migration, providing specific molecular
anchorage for moving cells
• Others keep cells on correct paths – inhibiting migration – use
nonmigratory cells
• Cell Adhesion Molecules (CAMs) – glycoproteins – help cell
migration and stable tissue structure
• Cadherins – important cell-to-cell adhesion molecule.
Developmental Fate of Cells
• Development requires a combo of morphogenetic changes
and the timely differentiation of cells in specific location
• 2 general principles
– Early cleavage divisions – Embryonic cells must become
different from each other
– Once initial cells asymmetries are set up, subsequent
interactions among the embryonic cells influence their fate
– usually causing changes in gene expression
A Cell’s Fate
• Fate Maps – diagram of embryonic development – reveals
future development of individual cells/tissues
• A cell’s fate can be changed by moving the cell to a new
location
• 2 Important conclusions
– Specific tissues of the older embryo can be attributed to certain early
“founder cells”
– As development proceeds a cell’s developmental Potential becomes
restricted
Establishing Cellular Asymmetries
• Establishing basic body plan is 1st step in morphogenesis – a
prerequisite for the development of tissues/organs
• Totipotent – describes a cell that can become any part of an
organism
• Zygote’s pattern of cleavage affects the fate of cells
• Progressive restriction of potency is a feature of development
in all animals
• The tissue-specific fates of cells in late gastrula are fixed
Inductive Signals
• Cell division creates cells that differ from each other  the
cells then influence each other’s fate (induction)
• Pattern Formation – development of an animal’s spatial
organization, arrangement of organs/tissues – influenced by
inductive signals
• Positional Information – Molecular cues – control pattern
formation
Limbs
• Limbs begin as bumps of tissue called Limb buds
• Buds – consist of a core of mesoderm tissue covered by a
layer of ectoderm – 2 organizer locations affect limb’s
development
• Apical Ectodermal Ridge (AER) – 1 organizer – thickened area
of ectoderm at the tip of the bud
• Zone of Polarizing Activity (ZPA) – other organizer – block of
mesodermal tissue located underneath ectoderm – posterior
side of the bud is attached to body
Citations
• http://www.vcharkarn.com/uploads/0/80.jpg
• http://3.bp.blogspot.com/_NDw_XebDkYI/S7ApTP1gibI/AAAAAAAAAO4/a
YitNrMkyWo/s1600/cleavage.jpg
• http://bio1152.nicerweb.com/doc/class/bio1152/Locked/media/ch47/47_
12FrogGastrulation.jpg
• http://bio1151.nicerweb.com/Locked/media/ch47/47_14FrogOrganogene
sis_CL.jpg