Vertebrate development

Question 1

What axis is distinguised in egg itself?

Answer 1

• Animal pole - named this as believed most of the nervous system derived from it
• Vegetal pole - denotes tissue that later forms digestive and ventral part of embryo

Question 2

How is dorsal-ventral axis formed?

Answer 2

sperm entry specifically at a certain position and triggers reformation of the cytoskeleton

Question 3

Important animal in developmental biology and why

Answer 3

Drosophila Melanogaster

• The larvae of this fly looks like this (worm like structure). We can already define segments by lit up areas - head and tail are clearly different from rest of the body.
  
  • Segments so easily visualised under microscope that it was utilised by geneticists to find mutations that would affect this segmentation (Nobel prize)

Question 4

Bicoid mutant of fly?

Answer 4

lacks anterior half of larvae

Question 5

Oskar mutant of fly?

Answer 5

entire thorical and abdominal segments are missing

Question 6

Gene cascade of early drosophila embryo

1)

Answer 6

Egg polarity genes - anterior and posteror ends - Bicoid protein high conc at anterior end - morphogen gradient. mRNA translated to protein when egg fertilised
There is a protein with opposite gradient to bicoid

Question 7

Gene cascade of early drosophila embryo

2-4

Answer 7

2) Gap gene activation - subdivides embryo
3) Gap gene activates pair rule gene - further subdivides
4) Segment polarity genes - define anterior and posterior end of each segment

Question 8

Gene cascade of early drosophila embryo activates what class of genes? What is their dunction

Answer 8

Homeotic selector genes (HSG). Need to specify where a head if forming, thorax, abdominal etc and the different organs within those structures.

Question 9

What is co-linearity

Answer 9

The order of genes on the chromosome is the same as the anterior border of their expression domains in the developing embryo. The reason for this colinearity is not yet completely understood

Question 10

What are Hox genes?

Answer 10

Transcription factors (TFs), the harbour a specific gene regulatory domain. Those TFs have the ability to bind to DNA with a. specific protein structure -in the case of Hox genes is called a homeobox.

Question 11

How are Hox genes orientated in drosophila

Answer 11

come in a cluster. There are 8 genes present here in this one chromosomal localisation.
- Co-linearilty in their positioning on chromosome and in their activation along anterior, posterior axis in the embryo

Question 12

Hox gene arrangement in vertebrates

Answer 12

4 clusters rather than 1
Most 3’ localised are activated anterior
Best seen in neural spine tube

Question 13

What does hox gene bind to?

Answer 13

specific DNA sequence and modulate gene expression of their target genes
- DNA binding domain called homeodomain

Question 14

Homeodomain structure

Answer 14

• consists of 3 helical parts (blue I,II,III) and only helix number 3 makes contact to DNA. Reads sequence in DNA and makes hydrogen bonds to specific nucleotides.

It has a recognition sequence, present in the DNA (red) and the protein (blue).

Question 15

Why is binding of Hox gene to homeodomain important?

Answer 15

Binding is important because TFs able to recruit RNA polymerase and entire apparatus required for transcription of a gene. These genes are able to activate genes required for development of specific segments. Activating them in a specific sequence along the anterior-posterior axis, we generate different structures of the developing embryo. Any misregulation results in serious alterations In the morphology

Question 16

Main model organisms for developmental biology?

Answer 16

Frog, Chick, Mouse, Zebrafish

Question 17

What is gastrulation?

Answer 17

1. movement of cells into the interior
2. Generation of novel neighbourhood relationship between cells
3. Lay down of embryonic axis - defines where dorsal and ventral is positions

Question 18

First step of development

Answer 18

Cell division

Question 19

Germ layers

Answer 19

Ectoderm - traditionally blue. Makes nervous system and skin and neural crest cells

Endoderm yellow - making the entire digestive tract and organs derived from digestive tract

Mesoderm - Most variable germ layer. Bones, kidney, RBC, myocardium. Also layers of muscles around endoderm that are derived from mesoderm

Question 20

Up until what cell stage are blastomeres totipotent in higher vertebrates and in frog egg

Answer 20

Up to 8 cell stage

- In frog egg - already fixed at fertilisation

Question 21

What is the Spemann-Mangold Organizer

Answer 21

Shows that this tissue is able to induce a gastrulation movement but also instruct the cells in the neighbourhood to form a second embryo. Coined the term organizer

Question 22

What does french flag model represent?

Answer 22

How morphogen gradients induces different cell identities in the embryo
- Set up as gradients - source where molecule (one e.g. of morphagen is bicoid) is at high conc and area where there is low conc and also area where there is a medium concentration.
- Cells eperience diff conc of this morphogen and respond by turning on different identities - blue, red or white identities.
So high concentrations of morphogens activate genes that are different from medium or low levels of the respective morphogen

Question 23

Example of french flag model

Answer 23

TGF-beta signalling molecule
Zebra fish injected with mRNA for TGF-beta signalling molecules. Embryo was incubated. Response of modification was studied.

When injected with 4pg - different genes activated in different cells.
If only 10.4mg, only purple present.
If we inject v high amounts, then only red activated.

Cells are able to receive how much signal they receive and activate specific genes in response to those amounts.
SO cells have a dose dependant response (gene activation) Leads to v different structures.