Introduction to Developmental Biology

Question 1

Differentiation

Answer 1

Of all the different cell types from a single fertilized egg (oocyte)

Question 2

Pattern formation

Answer 2

Precise arrangement of these cells into tissues and organs and placement of these tissues and organs within the organism

Question 3

Morphogenesis & growth

Answer 3

The process of bringing about changes in form and in the size of the developing embryo

Question 4

Epigenesis

Answer 4

de novo formation of an organism from “disordered” egg cytoplasm

Question 5

de novo

Answer 5

new, made from scratch

each organism is constructed from a disordered cytoplasm

Question 6

What does epigenetic control affect?

Answer 6

how/when/where a given gene is expressed in an organism

Question 7

Autonomous specification

Answer 7

Major role for maternal factors*

• *Morphogenetic determinants deposited in the egg cytoplasm by the mother which are segregated by cell division and/or distributed in a non-homogenous fashion prior to fertilization
• determination of cell fate occurs early during development
• cells removed from their original context will still maintain their original “identity” and give rise to the organ/structure they are specified for

Question 8

Conditional specification

Answer 8

Major role for the environment

• Cell fate determination occurs later and depends on the cell position in the embryo (interactions with other cells)
• Each cell has the potential to give rise to more cell types than it normally does
• If cells are “removed” from their original environment and transplanted into another part of the embryo they can change their “identity” and give rise to a different organ/structure than they were originally specified for

Question 9

asymmetric division (autonomous)

Answer 9

sister cells born different

Question 10

symmetric division (conditional)

Answer 10

sister cells become different as result of influences acting on them after their birth

Question 11

differential gene expression

Answer 11

cellular differentiation occurs despite each cell having equivalent genomes

Question 12

Specification

Answer 12

Changes in gene expression which are labile (can be altered). The expression of certain genes “allows” the cell to differentiate along a pathway but does not irreversibly commit the cell.

Question 13

Determination

Answer 13

Further changes in gene expression which seal the lineage fate of the cell and eliminate alternative choices (irreversible).

Question 14

Is specification autonomous or conditional?

Answer 14

Can be either

Question 15

Defect experiment

Answer 15

wherein one destroys a portion of the embryo and then observes the development of the impaired embryo

Question 16

Isolation experiment

Answer 16

wherein one removes a portion of the embryo and then observes the development of the partial embryo and the isolated part

Question 17

Recombination experiment

Answer 17

wherein one observes the development of the embryo after replacing an original part with a part from a different region of the embryo

Question 18

Transplantation experiment

Answer 18

wherein one portion of the embryo is replaced by a portion from a different embryo. This fourth technique was used by some of the same scientists when they first constructed fate maps of early embryos.

Question 19

Fate mapping

Answer 19

Tracking of cell movements during development to establish what they will give rise to in the adult animal

Question 20

Development

Answer 20

Fertilization: fusion of gametes (egg+sperm) to form a zygote with a unique genome

Cleavage: fast cell division, no increase in cell size. Gives rises to many smaller cells called blastomeres.

Blastula: One cell thick spheres made of blastomeres with an inner cavity (blastocele)

Gastrula: Slow down of mitosis follow by extensive rearrangements and movement of blastomeres migrating inside (“burrowing”) through a blastopore

Germ cell layers: End results of gastrulation. First stage of differentiation-

  - Ectoderm (outer): skin & nervous system
  - Endoderm (inner): gut, liver, lungs
  - Mesoderm (middle): Muscle, blood and bone

Question 21

Gastrulation

Answer 21

• Process that occurs early during development (once cleavage is completed) that puts cells into new positions, allowing inductive interactions to occur and determining cell fate in the developing embryo
• During gastrulation complex cell movements drastically modify the morphology of the embryo
• The result of gastrulation is the formation of three germ layers from which all of the organs of the embryo will arise

Question 22

Induction

Answer 22

The process whereby one group of cells signals to another group of cells in the embryo and so affects their development

Question 23

Juxtacrine signaling

Answer 23

cell-cell or cell-extracellular matrix interactions via receptors-ligand located at the cell membrane

Question 24

Paracrine signaling

Answer 24

Soluble molecules that affect cell fate within a certain distance. Link cell location to cell fate (morphogen gradients).

Question 25

Morphogen

Answer 25

Any substance active in pattern formation whose spatial concentration varies and to which cells respond distinctly at different levels