Chapter 8 - Early Development in invertebrates

• The next chapters examine early development in several models, including invertebrates (Ch. 8-9) amphibians (ch 10) and then vertebrates (ch. 11)

1 frog egg becomes ______ cells in __ hours!

Fig. 8.1

1. _____- One cell is subdivided into many cells to form a blastula

2. ___________- Extensive cell rearrangement to form endo-, ecto- and meso-derm

3. ___________- Cells rearranged to produce organs and tissue

4. ________________- produce germ cells (sperm/egg) Note: Somatic cells denote all non-germ cells

General Animal Development

Recall from lecture 1

How does egg undergo cleavage without increasing it’s ____?

• Answer- it abolishes ___ and ___ phases of ________.

• Do you need a cell cycle primer??

Four cell cycle phasesM- _________G1- __________- DNA Synthesis___- Gap 2

a. Cleavage

Reminder- mitosis occurs in __ phase, DNA replication in ____________

From Mol. Biol of the Cell by Alberts et al, p864

a. Cleavage

• _________________ (cdk, cdc) drive the cell cycle• But ________ (e.g cyclin A, B…) regulate cdk (cdc) activity

______________________________ (MPF= cyclin B+cdc2)

Example-

MPF

a. Cleavage

Again, how does egg undergo cleavage without increasing it’s size?

• Answer- it abolishes __ and___ phases of cell cycle

Cyclins are _________ in

eggs

Cyclins are _________

S phase

M phase

a. Cleavage

What actually drives the _______ process?

Answer- Two processes-

1. _________________ (mitotic division of the nucleus)

• The mitotic spindle (microtubules composed of tubulin) does this

2. __________ (mitotic division of the cell)

• ___________ “pinch off” (microfilaments composed of actin) Fig. 8.3

_____________ prevents cytokineses

a. Cleavage

1. Cleavage- One cell is subdivided into many cells to form a blastula

2. __________- Extensive cell rearrangement to form endo-, ecto- and meso-derm

3. Organogenesis- Cells rearranged to produce organs and tissue

4. Gameteogenesis- produce germ cells (sperm/egg) Note: Somatic cells denote all non-germ cells

General Animal Development

Recall from lecture 1

Gastrulation- cells of blastula are dramatically _______________• Three germ layers are produced

Five types of _____________

1 2 3

b. Gastrulation

GastrulationFive types of movements

4 5

b. Gastrulation

Axis formationThree axes must be determined-

• ___________________ (head-tail)• ________________ (back-belly)• ______________ (right side-left side)

Fig. 8.7

b. Gastrulation

Now let’s take a look at one beast- the ____________

• Cleavages 1 and 2 are through ______________ poles

• Cleavage 3 results in four ________ and four ______cells

1 2

3

Fig. 8.8

• Cleavage 8 _______ (animal pole) plus 4 _________ and 4 ____________ (vegetal pole)

4

1. Cleavage

• Post cleavage 5Fig. 8.9

Cell fate map

_______________ signal other cells via to influence fate

• Micromere cell fate is _____________- these become ____________ tissue if placed in a dish

• All other cells have ____________specification

Example- Transplant micromeres to animal pole at

___________ stage

•Micromeres cause a second __________•Animal pole cells become _______cells

Fig. 8.13

Sea urchin (continued)

EggLate

_______

________

Later stages

Fig. 8.16 Sea urchin development

2. Gastrulation

Note-micromeres produce ______

_________ which will become larval _______

How do __________ cells know to migrate inside

________?

Answer- changing cell ________________

___________

Extracellular matrix

Basal _____

Primary __________ cell

___________

98% decrease in ________ affinity100-fold increase in _____________ affinity

Fig. 8.19

How does __________ occur?Terms- •Invagination region is called _________•Opening created is called the ___________

Answer- swelling of inner _______ layer

Inner layerOuter layer

_______ cells secrete chondroitin sulfate proteoglycan, causing inner layer to swell and cause _________

________

Now let’s take a look at another creature- the nematode C. elegans

• ___cells at maturity• ____ long• Produces eggs and sperm (___________)• Transparent• __ hours from egg to hatch• Entire genome sequences- ___________ genes

What a great model!

1mm

Mature eggs passes through the ________ on the way to the _______

Germ cells undergo ______,

then begin meiosis as travel down _________

Oviduct

Cleavage

C. elegans

1. Cleavage

1. Cleavage

• Cleavages 1 produces _______ cell (AB) and ______ cell (P1)

• Cleavage 2 results in three _______ cells and one ______ cell (P2)

1 2 3

• Remaining cleavages result in a __________ cell and more founder cells

Fig. 8.42

C. elegans

How is the ___________________ axis determined? Answer- ___________- ribonucleoprotein complexes

•________ always stay associated with the “P” cell

Fig. 8.43

C. elegans

1

3

5

•____ proteins- these specify ______, cell ________ and cytoplasmic __________.

What directs the __________?

C. elegans

1. Cleavage

• P1 develops ________________

• AB does not (thus is ____________)

What drives P1 lineage?P granules? No, these do not enter ________!

Other possibilities• _____- a bZIP family transcription factor that control

EMS cell fate• ______ - a transcription factor required for P2 lineage• ______- inhibits SKN-1 and PAL-1 in P2

Yes- P2 produces a signal that tells ABp to only _______ and ________ cells, not pharynx like ABa

• _____ is the receptor on ABp, and _____ is the ligand on P2

GLP-1 is a ____family proteinAPX-1 is a _____family protein

Does P2 dictate fate of _________ cells?

An example of _________ signaling