Mechs of Embryogenesis

Question 1

Although drosophila, nematodes, and humans are obviously different, how many human genes are present in each of these species? What about humans relative to mice?

Answer 1

40%; 92% of human genes

Question 2

What four things do genes help govern? What do these four things depend on?

Answer 2

Cell proliferation, specialization, interaction, and movement; requires cell communication

Question 3

What is a good example of homogolous genes functioning interchangeably among species?

Answer 3

Mouse lacking Engrailed-1 for cerebellum development, but rescued by Drosophila engrailed!!!

Question 4

T/F: genetic material is identical in every cell, and different cells will express each of their genes; what is the notion called?

Answer 4

False: first phrase true, but different cells express different sets of genes;
genome equivalence (all cells with SAME SET OF GENES)

Question 5

What is the idea behind cloning?

Answer 5

Oocyte donor with an enuclated egg, and a nucleus from a donor fusing these two together before putting in a surrogate mother and allowing blastocyst to implant

Question 6

What is the idea behind differential gene expression?

Answer 6

While each cell has the same set of genes, only a small percentage of genome is expressed in a cell type (depending on the cell I suppose)

Question 7

At what four levels can gene expression be regulated?

Answer 7

Differential gene transcription, selective nuclear RNA processing, selective mRNA translation, differential protein mod

Question 8

What method can be used to detect mRNA expression?

Answer 8

RNA in situ hybridization, which could help detect specific mRNA expression depending on the cell/tissue

Question 9

Of the four things genes help govern, what is induction an example of? Define it

Answer 9

Interaction; one group of cells changes the behavior of an adjacent set of cells;

Question 10

Over what distances can induction work? What are the two components of induction? What must the target tissue have?

Answer 10

Short-range (cell-cell contacts) vs. long-range (signals go through EC medium);
inducer (tissue will help change behavior of target tissue) and responder (tissue being induced that must have competence)

Question 11

What does the optic vesicle do? What happens if you move the optic vesicle to different ectoderm, or if you remove the optic vesicle? What is the only tissue able to respond to optic vesicle signals?

Answer 11

It induces lens formation in head ectoderm; it will not induce lens formation;
Head ectoderm

Question 12

What allows ectoderm competent to respond to inductive signals?

Answer 12

Pax6 (actively acquired competence)

Question 13

What type of mutations in PAX6 leads to path? What is the path? What happens with homozygous loss of PAX6?

Answer 13

Autosomal dominant; aniridia (perhaps optic vesicle defect);

fatal condition with near complete failure of eye development

Question 14

What are two modes of signal transmission bewteen inducer and responder? What did he talk about?

Answer 14

Juxtacrine and paracrine; the latter (diffusion of inducers from one cell to another)

Question 15

What do morphogens do? What do they help set up among the cells? What can they help do at the genetic level for cells?

Answer 15

They are paracrines that act in concentration dependent manner; they help set up a concentration gradient and specify more than one cell type;
induce or maintain expression of different target genes at distinct concentration thresholds

Question 16

How can responder cells respond to signals sent from inducer?

Answer 16

Use signal transduction cascades: 1. EC signal molecule 2. receptor protein 3. IC signaling proteins (phosphorylation and whatnot) 4. Altered metabolism, gene expression, cell shape/movement

Question 17

What are some examples of signaling cascades?

Answer 17

TGF beta and SHH (former uses SMAD, gets phosphorylated, goes to nucleus; latter binds Patched, which inhibits Smoothened, and GLI goes to nucleus)

Question 18

What is expressed at the floor plate of neural tube? Roof plate? What happens then along the neural tube?

Answer 18

SHH; BMP and Wnt; different cell types with these morphogen concentration gradients

Question 19

What is the normal orientation of internal organs? What is the exact reverse and is it bad usually? What is a bad result of left-right asymmetry defects?

Answer 19

Situs solitus; situs inversus;

heterotaxy (situs ambiguus)

Question 20

What is a key to left-right asymmetry?

Answer 20

Asymmetric gene expression (differential gene expression)

Question 21

What appears to be conserved for cardiac L-R symmetry?

Answer 21

Asymmetric looping to right after bilateral tubes form linear tubes

Question 22

What is Kartagener’s triad? What do the symptoms suggest?

Answer 22

Bronchiectasis, infertility, situs inversus;

ciliary beating could control which way left-right axis is oriented

Question 23

What is found on cells at the primitive node?

Answer 23

Cilia, driving fluid to left side!!!

Question 24

What can asymmetric flow help establish at the node?

Answer 24

Morphogen gradient orienting LR axis of body

Question 25

What signaling cascade is involved with LR patterning? What does it turn on? What do these products help do?

Answer 25

Nodal; turns on Pitx2 and Lefty;
latter will regulate Nodal expression in the heart, while Pitx2 can be expressed on left side of heart, gut brain to mediate asymmetry