Lecture 35 - Development of Multicellular Organisms I

Question 1

What are the main steps in the development of an embryo?

L35 S5

Answer 1

• cell proliferation
• cell specialization
• cell interaction
• cell movement

Question 2

Describe the structure of a blastula and what changes occur to change it into a gastrula.

L35 S10+12

Answer 2

Blastula:
-hollow sphere of cells

Gastrula

• outer part of sphere becomes ectoderm
• part of outside folds in, becoming endoderm
• some cells break off into the space between and become mesoderm

Question 3

What tissues arise from the ectoderm, mesoderm, and endoderm?

L35 S12

Answer 3

Ectoderm:

• nervous system
• epidermis

Mesoderm:

• muscles
• connective tissue

Endoderm:
-gut, lung, liver

Question 4

Differentiate between determined, completely undetermined, and committed cells.

L35 S19

Answer 4

Determined:
-will develop into a specialized cell type regardless of changes in environment

Completely undetermined:
-rapidly responds to changes in environment

Committed:
-have attributes of a specialized cell type but can still respond to changes in the environment

Question 5

What are the main two mechanisms for cell differentiation?

L35 S23

Answer 5

Asymmetric division:

• molecules significant to differentiation unevenly distributed between daughter cells
• eg. germ cells

Symmetric division:
-daughter cells differentiate based off external, environmental events after they split

Question 6

What is a morphogen?

L35 S28

Answer 6

• long range inductive signal

- produces a gradient which can stimulate cells to differentiate into several developmental pathways

Question 7

What is the effect of lateral inhibition?
What is an example of this?

L35 S32

Answer 7

• neighboring cells express the same external signals
• the external signals inhibit other cells from expressing that signal
• eventually one cell wins out and is the only neighboring cell expressing that signal

-this process is used in differentiation of neurons and glial cells in the form of Delta Notch signaling where only the cells that express delta become neurons

Question 8

What is sequential induction?

L35 S37

Answer 8

• differentiated cell B induces differentiated cell A to produce differentiated cell A
• differentiated cell C induces differentiated cells A and B to produce differentiated cells D and E