Mechanisms of Development

Question 1

similarities across species

Answer 1

• vertebrate species begin with similar structure but become less alike each other as they develop
• similar genes and mechanisms have been found to control similar developmental processes in different animals

Question 2

genetic similarity

Answer 2

• similarity in dramatically different animals
• 20,000 genes in humans and nematodes
• 14,000 in fruit fly
• ~40% of human genes are present in flies and worms
• ~92% of human genes present in mice
• of 4,000 genes studied, less than 10 are in one species and not the other
• both mouse and humans have 3.1 million bp and similar number of genes

Question 3

mechanisms that drive developmetn

Answer 3

• genes and environment
• cell proliferation, specialization, interaction, and movement
• carried out by cell-cell communication

Question 4

homologous genes

Answer 4

• function interchangeable during development of different species
• gene similar in structure and evolutionary origin (and likely function)
• drosophila gene in mouse embryo has same effect as original gene

Question 5

model organisms

Answer 5

-due to similar mechanisms of development and homologous genes, researchers can use model organisms to study embryology under the premise that genes and mechanisms that control a specific aspect of development in one species are likely to play a similar role in that process in other species

Question 6

how do genes drive development?

Answer 6

• before genome sequencing, there were 2 hypothesis
  1. difference in cell type comes from different sets of genes in different cells, and some cells lose genome
  2. genes in all the cells are the same, they are just expressed differently- turns out to be the right one

Question 7

genome equivalence

Answer 7

• all cells contain the same set of genes

- different cells express different sets of genes

Question 8

somatic nuclear transfer

Answer 8

• aka cloning
• provides evidence that all cells contain the same genes
• cuz they can take somatic cell and put it in an egg and make it grow
• electrical pulses activated development
• nuclei of vertebrate adult somatic cells contain all of the genes necessary to generate and adult organism- no genes necessary for development have been lost

Question 9

differential gene expression

Answer 9

• only a small percentage of the genome is expressed in a cell type
• regulatory regions and proteins
• controls fundamental cellular processes-proliferation, movement, specialization, interaction

Question 10

gene expression regulation

Answer 10

• differential gene transcription
• selective nuclear RNA processing
• selective mRNA translation
• differential protein modification
• RNA in situ hybridization is a technique used to detect mRNA expression in cells/tissues

Question 11

induction

Answer 11

• one group of cells changes the behavior of an adjacent set of cells
• can be short range or long range
• need inducer, responder, and the responder cells have to be competent- have ability to receive signal

Question 12

ectodermal competence and the ability to respond to optic vesicle inducer

Answer 12

1. normal induction of lens by optic vesicle
2. optic vesicle can’t induce ectoderm that isn’t competent/ in the wrong place
3. if there is no optic vesicle, no induction
4. tissue other than optic vesicle doesn’t induce ectoderm

Question 13

competence

Answer 13

• actively acquired
• pax6 makes ectoderm competent to respond to inductive signals from optic vesicle
• one copy leads to aniridia
• no pax 6 means no eye

Question 14

signal transduction

Answer 14

• juxtacrine-contact between cells

- paracrine- diffusion of inducers

Question 15

paracrine factors

Answer 15

• proteins that are secreted into extracellular space and deliver signals to neighboring cells
• all morphogens are paracrine signals but not all paracrine signals are morphogens

Question 16

morphogens

Answer 16

• paracrine signaling molecules that cause concentration dependent effects
• those with the highest concentration are different cell types than those with less morphogens
• experimental id- inject the mRNA and watch. if the protein is made and secreted and causes concentration dependent effects, its a morphogen

Question 17

signal transduction cascade

Answer 17

• all variations on a common theme
• signal receptor molecules bind ligand
• changes conformation of receptor
• often gives it enzymatic activity
• active receptor kicks off cascade of enzymatic processing of several intracellular proteins, which ultimately activates a transcription factor in the nucleus that binds DNA and alters gene expression in the cell
• can be metabolic enzymes, alter gene expression, or alter shape and movement
• whole cascade makes cells competent, not just receptor

Question 18

BMPs/nodal

Answer 18

• TGFb family
• activate SMAD 2/3
• becomes phosphorylated
• goes to nucleus and increases gene expression

Question 19

SHH

Answer 19

-activates patched which inhibits smoothened and allows GLI to become a TF in the nucleus

Question 20

symmetries along left/right axis

Answer 20

• many internal organs are asymmetric along right/left axis
• situs solitus vs inversus vs heterotaxy (which is just other)
• congenital heart defects
• if you duplicate R- no spleen
• duplicate L- two spleens
• volvulus or other gut problems

Question 21

morphogens in neural tube

Answer 21

• BMPs and WNT at roof plate
• SHH at floor plate
• specifies different cell types in neural tube

Question 22

altered symmetric gene expression

Answer 22

-correlates with altered organ asymmetry

Question 23

nodal

Answer 23

• only expressed on the L side in lateral plate mesoderm
• tightly regulated
• development of heart has left-right looping in all vertebrates
• molecular signal tells tube which way to turn

Question 24

kartagener’s syndrome

Answer 24

• brochiectasis
• infertility
• situs inversus in 50%
• cilia??
• movement of cilia in embryo help determine L-R axis
• men are infertile- immotile sperm

Question 25

cilia in development

Answer 25

-present in primitive node and pit
-fluid goes from right to left
-cilia move in that direction
-nodal is expressed at the left end due to cilia beating
how?
-morphogen gradient?

Question 26

nodal 2

Answer 26

• signaling cascade involved in L-R patterning
• nodal positive feedback on itself
• lefty negative feedback
• keeps nodal in strip on left side of mesodermal plate
• Pitx2 links outcome of nodal/lefty interactions to subsequent anatomical development
• TF pitx2 is expressed on left of developing heart, gut, brain
• Calcium plays a role too