Lectures 1-2 (Quiz 1)

Question 1

What are the two pillars of genetics and development?

Answer 1

Cell theory and the theory of evolution

Question 2

What is development?

Answer 2

Process by which multicellular organisms change and grow. Generates different cell types from single cell. Cells specialized for different functions. Cells are then organized into tissues, which are organized into organs.

Question 3

Do single celled undergo development?

Answer 3

Yes. They do need to generate different cell types. During the cell cycle, development happens.

Question 4

What is the central dogma of molecular biology?

Answer 4

Genetic information flows in one direction. DNA is transcribed to RNA, and RNA is translated to protein.

Question 5

If all cells in multicellular organisms have the same genome, how does development occur (how are cells different)?

Answer 5

Differences in gene expression generates differences in cell type/function.

Question 6

What are some tools to study development?

Answer 6

Observation (microscopy, staining), Physical perturbations (transplantation, ablation), genetics, bioinformatics.

Question 7

What is a loss of function mutation vs. a gain of function mutation?

Answer 7

LOF: No functional product produced from gene // decreased gene activity
GOF: Increased gene activity / product.

Question 8

What do phylogenetic trees show?

Answer 8

They show when populations split and evolved into new species. Based on anatomy, fossil record, and molecular evidence.

Question 9

What is modularity?

Answer 9

The idea that the molecular pathways that determine development processes operate independently

Question 10

How does morphological evolution occur?

Answer 10

New genes/pathways don’t pop up: Existing genes and pathways are modified.

Question 11

How does development of complex organisms start?

Answer 11

Starts with a single egg (fertilized eg or zygote). Eventually this single egg generates different cell types and organizes them into a 3D body.

Question 12

What is totipotency. What early developmental entity is totipotent?

Answer 12

Zygotes are totipotent, meaning they are capable of giving rise to every cell type.

Question 13

How does development occur in single celled organisms?

Answer 13

Certain single celled organisms exist in two forms (vegetative vs. sporulating)

Question 14

What is determination (in the context of development)?

Answer 14

To set the fates of cells or what they will become (because of differential gene expression).

Question 15

What is differentiation (in development)?

Answer 15

To acquire specific cellular structures and functions because of differential gene expression.

Question 16

What is morphogenesis?

Answer 16

To organize and spatially distribute specialized cells (through cell division, expansion, movement, and death)

Question 17

What is growth (in development)?

Answer 17

To increase body and organ size (through cell division and growth).

Question 18

How can we distinguish different cell types?

Answer 18

Histological staining, in situ hybridization, immunolocalization, biochemical activity monitoring, reporter gene fusion

Question 19

How do we identify candidate genes?

Answer 19

Using forward or reverse geneticcs

Question 20

What is the difference between forward and reverse genetics?

Answer 20

Forward genetics screens for a gene on the basis of a trait/phenotype, while reverse genetics mutates a gene to analyze its phenotypic effects.

Question 21

What are three ways to determine a gene’s function?

Answer 21

Expression patterns (figuring out when/where they are expressed), LOF studies, and GOF studies

Question 22

How would one determine expression patterns?

Answer 22

In situ hybridization, immunostaining, and reporter studies (promoter fusion or biochem assay)

Question 23

What are the 2 main ways that cells can be different, and how do they come about?

Answer 23

Cells can be different at birth. This happens via intrinsically asymmetric cell division or temporal regulation. Cells can also be identical initially, and later differentiate through via external signaling (secreted factor direct cell-cell contact)

Question 24

How does external signaling rregulate cellular differentiation?

Answer 24

Through signal transduction. Macromolecules cooperate to regulate gene expression.

Question 25

Where do transcription factors bind in order to affect gene expression?

Answer 25

They bind to specific regulator regions of a gene - promoters and enhancers.

Question 26

In mammalian embryonic development, when does the first differentiation occur?

Answer 26

The first differentiation occurs after the 8-cell stage

Question 27

What is formed during the first differentiation (during mammalian embryonic development)?

Answer 27

An outer TE (trophectoderm) layer and an inner cell mass (ICM) layer are both formed.

Question 28

What is the ICM (inner cell mass)?

Answer 28

It is the source of embryonic stem cells, which are capable of generating all cell types within the embryo.

Question 29

What are the four main steps of nervous system development?

Answer 29

Neural induction, patterning along the body axes (generating distinct regions of the nervous system), diversification of neural cells in each region (making distinct types of neurons and glia), and making connections.

Question 30

What factors matter in choosing a model organism for paste experiments?

Answer 30

Embryo location, source of food for embryos, size of embryo, and speed of embryonic development

Question 31

What are the three germ layers of early development? What does each layer give rise to?

Answer 31

The endoderm, mesoderm, and ectoderm. Endoderm becomes intestines, lungs, liver, etc. Mesoderm becomes somites (vertebrae, dermis, muscle), genital ridge, kidney. Ectoderm becomes skin and nervous system.

Question 32

Describe the embryonic axes for a fertilized frog egg?

Answer 32

The ectoderm, mesoderm, and endoderm are all on the interior, with ectoderm on top and endoderm on the bottom. The animal pole is on the anterior side, sperm entry is on the ventral side, future organizer on the dorsal side, and vegetal pole on the posterior side.

Question 33

What are the two fate choices for ectoderm? Which side do each of these cell types emerge from?

Answer 33

Differentiating into neural or epidermal cells. epidermal cells emerge from the ventral side, while neural cells emerge from the dorsal side.

Question 34

Where is the dorsal blastopore (aka Spemann-Mangold organizer) located?

Answer 34

On the dorsal side of the mesoderm layer. Contains both mesoderm and endoderm cells.

Question 35

What is the Spemann and Mangold Experimence?

Answer 35

This was a grafting (cut and paste) experiment. They transplatned another dorsal lip to the ventral side of the host embryo to determine if the dorsal lip was in fact responsible for organizing/inducing the nervous system (i.e. ie causing/preventing neural or epidermal induction in germ cells) .

Question 36

What are the indirect effects of neural induction?

Answer 36

Growth factors like Activin and Vg1 can induce mesoderm. The mesodermal cells then induce neural tissue.

Question 37

What are some direct effects of the neural induction?

Answer 37

Activin is a member of the TGF beta family of growth factors. A truncated type II activin receptor inhibits activin signaling. Delta XAR1 inhibits mesoderm formation and directly induces neural tissue.

Question 38

What is the animal cap dissociation assay?

Answer 38

The animal germ cell layers contain an animal cap and a vegetal pole. Scientists compared the intact cap to a dissociated cap and found that the former was epidermal tissue, while the latter become neural tissue.

Question 39

What are two ways that inhibition of signaling can cause neural induction?

Answer 39

1. delta XAR1 can inhibit other TGF beta factors. It inhibits Vg1 and BMPs. TGF beta family members are expressed in other germ layers.
2. As shows by the animal cap dissociation assay, dissociated ectodermal explants form neural tissue, while intact or whole animal caps form epidermis.

Question 40

Which is the induced vs default state for ectodermal cells? What signaling allows for the induced state?

Answer 40

Neural is the default (ground state), while epidermal is the induced state. BMP signaling allows ectodermal cells to choose epidermal fates.

Question 41

How does the dorsal blastopore lip (Spemann-Mangold organizer) cause neural induction?

Answer 41

The Spemann Organizer secretes BMP4 antagonists. BMP4 signaling is responsible for epidermal induction, so suppressing this signaling causes nearby ectodermal cells to adopt the default neural state.

Question 42

What are the noggin and chordin in mice, and what is their role?

Answer 42

The chordin/noggin is the mouse equivalent of the Spemann-Mangold organizer in frogs. It expresses inhibitors of BMP signaling (like in frogs).

Question 43

For the double knockout experiment of two noggin and chordin genes, why were there no defects in neural induction?

Answer 43

Functional redundancy!
1. Multiple antagonists to inhibit BMP signaling
2. BMP antagonists vs direct regulation of transcription
3. Multiple signaling pathways (BMP, Wnt, Fgf)