4 Embryo

Front 1

Important transitions

Back 1

1. Germ layers and tissue development

2. Body symmetry

3. Body cavity

4. Opening of mouth or anus

5. Segmentation

6. Adaptions to environment

Front 2

Germlayers

Back 2

Ectoderm - body coverings and nervous system

Mesoderm - skeleton and muscles

Endoderm - digestive organs and intestines

Front 3

Diploblastic

Back 3

Only ectoderm and endoderm

Front 4

Triploblastic

Back 4

All three germ layers present

Front 5

1. Tissue development

Back 5

Parazoa - sponges, undefined tissues and organs, can disaggregate and aggregate their cells

Eumetazoa - all others, 3 germ layers, irreversible differentiation for most cell types

Front 6

2. Body symetry

Back 6

Parazoa lack definite symmetry

Eumetazoa - radial and bilateral symetry

Front 7

Radial symmetry

Back 7

Body parts arranged around central axis

Bisected into two equal halves in any 2D plane

Front 8

Bilateral symmetry

Back 8

Body has right and left halves that are mirror images

Midsagittal plane bisects animal into 2 equal halves

Front 9

Bilaterally symmetrical animals have

Back 9

Anterior/ posterior (head-tail)

Dorsal/ventral (top-bottom)

Left/Right (lateral)

Poximal/ distal body appendages (close-far)

Cephilization (head development) and greater mobility

Front 10

3. Body cavity

Back 10

Acoelomates - no body cavity

Pseudocoelomates - body cavity between meso and endo called pseudocoelom

Coelomates - within mesoderm, coelom, development of advanced organ systems

Front 11

4. Patterns of development (Bilaterally symmetrical)

Back 11

Protostomes - mouth first from blastopore, anus if present develops from elsewhere, flatworms

Deuterostomes- anus first from blastopore, mouth later from elsewhere, chordates

Front 12

Protostomes

Back 12

Majority coelomate invertebrates

Spiral cleavage

Determinate development

Front 13

Deuteostomes

Back 13

Echinodermata and chordata

Radial cleavage

Indeterminate development - 8 cell embryo cells are totipotent, can arise to become a whole organism

Front 14

5. Segmentation

Back 14

Advantages:

1. Allows redundant organ systems in adults

2. Allows more efficient and flexible movement

Front 15

6. Adaption to environment

Back 15

Marine - hospitable, small yolk, external fertilization, no egg protection, larvae

Fresh water - less hospitable, moderate yolk, external/internal, egg retained or attached to substrate, sometimes

Terrestrial- inhospitable, large yolk, internal, enclosed or internal or laid, insects

Front 16

Gene expression is controlled at many levels,

Change in gene expression causes changes in

Back 16

cell shape

metabolism

activity

motility

Changes apparent in daughter cells and neighboring cells

Front 17

Autonomous specification

Back 17

Due to cytoplasmic components of egg

Invertebrates

No large scale embryonic cell migration

Front 18

Conditional specification

Back 18

Interactions between cells, relative positions are important

Vertebrates and few invertebrates

ell migrations

Front 19

Syncytial specification

Back 19

Insects

Interactions between cytoplasmic environment

Front 20

Invagination

Involution

Ingression

Delamination

Epiboly

Back 20

In-folding

Inward movement of outer layer expanding

Migration of individual cells to interior

Splitting one sheet into two

Epithelial sheets spread to enclose deeper layers

Front 21

Urchin cleavage

Back 21

Holoblastic isolecital radial cleavage

Divisions 1 and 2 are meridional and perpendicular

3 is equatorial and perpendicular

Front 22

Urchin devision 4

Back 22

4 animal pole cells divide meridionally - 8 mesomeres

Vegetal - unequal equitorial devision, 4 macro and 4 micromeres

2 large (autonomous) , 2 small micromeres- stop after 5th

Front 23

Fate

Animal half

Veg 1

Veg 2

Large micromeres

Small micromeres

Back 23

ectoderm

ectoderm and endoderm organs

endoderm, coelom, 2nd mesenchyme

Larval cytoskeleton

Contribute to coelom

Front 24

Blastula formation sea urchin

Back 24

After 7th division, blastocoel forms

All cells contact fluid inside and hyaline layer

Divide, one cell thick, develop cilia, blastula rotates

Vegetal cells thicken, animal cells secrete hatching enzyme

Front 25

Gastrulation sea urchin

Back 25

Large micromeres extend filopodia, dissociate from monolayer

Ingression of primary mesenchyme cells forms larval skeleton

Hatch from fertilization envelope

Leads to epithelial to mesenchymal cell transition

Front 26

Filopodia

Back 26

Formed when primary mesenchyme cells lose affinity for hyaline layer and migrate

Senses direction and pattern cues, cluster, travel along blastocoel wall to ventral paracrine factors

Front 27

Vegetal cells invaginate

Back 27

caused by change in shape of cells and extracellular matrix

1/4-1/2 of the way, froms archenteron

Opening is blastopore

Front 28

Archenteron

Back 28

Primitive gut

extends dramatically via convergent extension and intercalation

Becomes long thin tube

Front 29

Secondary mesenchyme cells

Back 29

extend filopodia pulling up archenteron

Front 30

Large micromeres

Back 30

Autonomous- not influenced by neighbouring cells

Influence other cells

When moved to animal pole, they generate endoderm, invagination

Front 31

Beta catenin

Back 31

Transcription factor of wnt signaling pathway

Sea urchin- found in vegetal, become endoderm and mesoderm

accumulation is autonomous, specifies vegetal side

Without it cells become ectoderm.

In animal will transduce the same reaction