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Wolpert: Principles of Development 3e

Chapter 08

Instructions

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Question 1

Which of the following cells would be considered differentiated?

a) Blastomere.

b) Spemann organizer.

c) Myotome of the somite.

d) Muscle cell.

e) Stem cell.

Question 2

Differentiated cells express the genes and proteins characteristic of their final identity in the adult, and that identity can be altered only under special circumstances. How does the concept of differentiation, as described here, differ from the concept of determination?

a) Determined cells have begun to differentiate, but are not fully differentiated.

b) Determined cells are embryonic cells that will give rise to all the cell types of the adult organism, but have not yet begun to express the genes and proteins characteristic of their final fates.

c) Determined cells will continue to follow their fate if grafted into a different place in a host embryo, even though they do not yet express the genes and proteins characteristic of their final fate.

d) Determined cells are embryonic cells that will form certain cell types and structures if development is allowed to proceed normally, but will alter their development in response to their location if transplanted to a different place in a host embryo.

e) Determination describes fully differentiated cells whose identity can no longer be altered.

Question 3

What is the role of stem cells with regard to the function of adult tissues and organs?

a) Stem cells are undifferentiated cells that divide asymmetrically, giving rise to one daughter that remains a stem cell and one daughter that will differentiate to replace damaged and worn out cells in the adult tissue or organ.

b) Stem cells are embryonic cells that persist in the adult, and can give rise to all of the cell types in the body.

c) Stem cells are determined cells that reside in fully differentiated tissues and can, when needed, differentiate to supply new cells for growth of the tissue.

d) Stem cells are differentiated cells that have yet to express the genes and proteins characteristic of their differentiated state, and do so when needed for repair of tissues and organs.

e) Stem cells are fully differentiated cells that reside under the surface of epithelia, in position to take over the function of the tissue when the overlying cells become damaged or worn out.

Question 4

The immunoglobulin genes are expressed in B-cells, and the β-globin gene is expressed in red blood cells. What manipulations might be carried out to get the β-globin gene to be expressed in B-cells?

a) The coding region of an immunoglobulin gene could be combined with the cis-regulatory region of the β-globin genes, and this artificial gene would then express β-globin in B-cells.

b) The cis-regulatory region of the β-globin gene could be inserted into B-cells, which would then express their own version of the β-globin gene.

c) The cis-regulatory region of an immunoglobulin gene could be combined with the coding region of the β-globin genes, and this artificial gene would then express β-globin in B-cells.

d) The transcription factors GATA-1 and GATA-2 (which activate the β-globin gene in erythrocytes) could be introduced into B-cells, which would then express their own copy of the β-globin gene.

e) Changing the colony stimulating factors present in the medium in which B-cells are growing could be manipulated in a way that would cause the B-cells to reverse their differentiation, become erythrocytes, and express β-globin.

Question 5

Imagine that in an attempt to get the β-globin gene to be expressed in B-cells (see question 4 above), the transcription factors (GATA-1 and GATA-2) known to control the β-globin gene in erythrocytes were introduced into B-cells, yet the β-globin gene was not expressed. What is a likely explanation for this result?

a) The erythrocyte transcription factors are degraded rapidly in the B-cell, and so cannot act on the β-globin gene.

b) The β-globin gene in the B-cells is packaged into heterochromatin, and the erythrocyte transcription factors are insufficient to remodel that chromatin into an active state.

c) Erythrocyte transcription factors cannot interact with their target DNA sequences in B-cells, even though those sequences are present and accessible.

d) Even though the necessary erythrocyte-specific transcription factors are now present in the B-cells, the general transcription factors required for β-globin gene expression would not be present.

e) The cis-regulatory regions for the β-globin gene are present only in erythrocytes, and not in B-cells, so the erythrocyte transcription factors would be meaningless in a B-cell.

Question 6

What type of cell-cell signaling protein exerts its effect in gene expression through a receptor that is a transcription factor?

a) The Wnt protein.

b) The Hedgehog protein, whose receptor is Patched.

c) Peptides like EGF and FGF, whose receptors are tyrosine kinases.

d) Hydrophobic molecules like steroid hormones and retinoic acid.

e) TGF-β family proteins like BMP and nodal.

Question 7

What is the developmental pathway by which the hematopoietic stem cell gives rise to a macrophage?

a) The hematopoietic stem cell divides, giving rise to a daughter cell that remains a stem cell and a daughter cell that differentiates directly into a macrophage.

b) The hematopoietic stem cell can give rise to either a lymphoid progenitor or a myeloid progenitor; the myeloid progenitor differentiates directly into a macrophage.

c) The hematopoietic stem cell can follow two paths, one called lymphoid and the other called myeloid, either of which can ultimately give rise to macrophages and other cell types such as osteoclasts and T cells.

d) The hematopoietic stem cell gives rise to a variety of cells referred to as granulocytes, any one of which can differentiate further into a macrophage.

e) The hematopoietic stem cell must first generate a cell of the myeloid lineage (as opposed to the lymphoid lineage), then a granulocyte/macrophage progenitor, then a monocyte, and finally a macrophage.

Question 8

Hematopoietic stem cells can be isolated and grown in culture; if one wished to control their differentiation into either neutrophils or macrophages, what colony stimulating factors could be used?

a) First, GM-CSF and IL-3 would be added to trigger formation of the granulocyte/macrophage lineage; then, the addition of either G-CSF or M-CSF would select between further differentiation as neutrophils or macrophages, respectively.

b) Since stem-cell factor (SCF) would maintain the cells as stem cells, the elimination of SCF would trigger differentiation into granulocyte/macrophage precursors; no further manipulation would be necessary.

c) The stem cells could be simultaneously stimulated with G-CSF, M-CSF, GM-CSF, and IL-3; half would become neutrophils and the other half would become macrophages; no further control is possible.

d) Since hematopoietic stem cells can become only erythrocytes, neutrophils, or macrophages, and no other cell types, the elimination of erythropoietin (EPO) would be sufficient to trigger formation of neutrophils and macrophages.

e) The addition of M-CSF alone to the medium would cause all the cells to become macrophages, whereas the addition of G-CSF would cause all the cells to become neutrophils; no other manipulation would be necessary, since this is the only difference between the two lineages.

Question 9

What is globin gene switching?

a) Globin gene switching refers to the switching on of the globin genes during erythrocyte differentiation.

b) Globin gene switching refers to the switching from α-globin to β-globin, so that α₂β₂ hemoglobin can be made.

c) Globin gene switching refers to the molecular basis for the genetic disease, sickle cell anemia.

d) Globin gene switching refers to the transition, during fetal development, from the production of hemoglobin containing ε-globin, to γ-globin, to β-globin.

e) Globin switching refers to a genetic rearrangement in the DNA that joins different segments of DNA, resulting first in ε-globin synthesis, then γ-globin synthesis, and finally β-globin synthesis.

Question 10

What do 'V', 'J', and 'C' mean in the context of the genes for immunoglobulins?

a) V, J, and C are the three exons of an immunoglobulin gene, which are spliced together to produce a mature immunoglobulin mRNA.

b) There are several V and J exons in an immunoglobulin gene; one of each is joined to a C exon during splicing, through a process of alternative splicing.

c) There are several V and J exons in an immunoglobulin gene; one of each is selected during a rearrangement in the DNA to produce an immunoglobulin gene capable of being expressed; the V and J segments that are not selected are lost from the genome.

d) The V and J genes exist in many copies; the choice of one of these many genes contributes to antibody diversity.

e) The immunoglobulin molecule is made of a heavy chain, encoded b the larger V region, and a light chain, encoded by the smaller J region; both chains contain a C region.

Question 11

Where are the stem cells that renew the epithelium of the gut found?

a) In the bone marrow,

b) In the inner cell mass.

c) In the villi, underlying the dead outer layer of keratinocytes.

d) Near the bottom of the crypt.

e) In the connective tissue underlying the gut epithelium.

Question 12

What happens if you introduced the gene myoD into fibroblast cells growing in culture?

a) The fibroblasts will express muscle-specific proteins, fuse, and form functional muscle in culture.

b) Nothing will happen because fibroblasts are derived from a different cell population in the embryo than are the muscle precursors that respond to myoD.

c) The fibroblasts will undergo apoptosis, due to the abnormal effects of myoD on their normal differentiation.

d) myoD will activate expression of myogenin, but the muscle-specific genes will not be able to activate.

e) Nothing will happen because fibroblasts do not have the genes required to become muscle.

Question 13

In what way are mrf4, myoD, and the other muscle-inducing genes similar to the homeotic genes of Drosophila?

a) mrf4, myoD, and the others encode homeobox- containing proteins.

b) mrf4, myoD, and the others encode 'master-switch' transcription factors, which initiate a cascade of gene expression that leads to the differentiation of cells.

c) mrf4, myoD, and the others act as homeotic genes in Drosophila.

d) mrf4, myoD, and the others are expressed exclusively in muscle, as are the homeotic genes of Drosophila.

e) There is no similarity between mrf4, myoD, and the others, since mrf4, myoD, and the others are strictly vertebrate genes while the homeotic genes are strictly Drosophila genes.

Question 14

Neural crest cells that follow a dorso-lateral route of migration under the skin will become melanocytes; how is their differentiation into melanocytes triggered during their migration?

a) The neural crest cells are already determined to become melanocytes before they leave the neural tube.

b) N-cadherin and E-cadherin are lost from the neural crest cells when they initiate their migration, and this signals the cells to become melanocytes.

c) BMP and noggin control the fate of neural crest cells.

d) The cells in the skin express a ligand (stem cell factor, SCF, also known as Steel) on their surface, which interacts with a receptor (Kit, also known as white spotting) on the surface of the neural crest derived cells; this interaction triggers their differentiation as melanocytes.

e) Melanocyte differentiation is the default pathway for neural crest cells, and requires no special trigger to occur.

Question 15

What is the difference between apoptosis and necrosis?

a) Apoptosis is a controlled program of cellular destruction; necrosis is cell death due to damage.

b) Apoptosis is a property of all differentiated cells; necrosis only occurs to undifferentiated cells.

c) Apoptosis is cell death due to damage that occurs during embryogenesis; necrosis is cell death due to damage that occurs during adulthood.

d) Apoptosis is the death of a differentiated cell; necrosis is the death of an undifferentiated cell.

e) Apoptosis is a term used to refer to necrosis that happens during development.

Question 16

What is the role of the caspases in apoptosis?

a) Caspase is a term used to refer to the initial signal that causes apoptosis.

b) Caspases are enzymes that are inactivated during apoptosis, and in their absence the cell dies.

c) Caspases are inhibitors of apoptosis; the destruction of the caspases causes apoptosis to begin.

d) Caspases are mitochondrial enzymes that are released when apoptosis is triggered.

e) Caspases are proteases that carry out the controlled destruction of the cell's components during apoptosis.

Question 17

What important lesson for the mechanisms of development can we derive from the ability to clone frogs by nuclear transfer?

a) That the selective gene expression seen in differentiated cells does not result from an irreversible loss of genes, or their potential for expression.

b) That a piece of a frog can be 'planted' to obtain a new, cloned individual, just like in plants.

c) That the pattern of gene expression in a differentiated cell can only be reversed if the nucleus is removed from the cell.

d) That the mechanisms of development are irreversible in all organisms except frogs.

e) That a differentiated frog nucleus can be used to clone any species of animal, proving that development is directed by the egg, not by the nucleus.

Question 18

Recently, it was reported that adult, differentiated cells can be made to behave as pluripotent stem cells by the introduction of a few genes, one of which was Oct4. What was the rationale for this experiment?

a) Oct4 is a master switch gene that turns on the stem cell program.

b) Oct4 expression is one of the requisites for the maintenance of pluripotent embryonic stem cells in culture.

c) The Oct4 gene produces a cell-cell signaling protein that is used by stem cells to stimulate cell division.

d) Oct4 is only expressed in embryonic stem cells, and so its expression automatically reverses any differentiation that may have gone on in a cell.

e) The Oct4 gene is lost from differentiated cells through a genomic rearrangement, and its reintroduction reverses that rearrangement and hence differentiation.

Oxford University Press, Online Resource Centre, Chapter 08.