Chapter 6 Self-test questions

. What is the difference between apoptosis and necrosis?

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

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

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

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

. What is the role of caspases in apoptosis?

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

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

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

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

. C. elegans is best known for

its formation of an inductive signaling center analogous to the organizer of Xenopus

its fully defined cell lineage during development

the large size and easy manipulation of its blastomeres

its mechanisms of metamorphosis

. P granules of nematodes are

determinants of the antero-posterior axis

determinants of the germ line

precursors of TGF-â family signaling proteins

remnants of the sperm pronucleus

. In flies, frogs, and chicks, gradients of morphogens determine the future antero-posterior and dorso-ventral axes of the developing embryo. How is the antero-posterior axis determined in C. elegans?

Bicoid protein is translated in the anterior of the fertilized egg, leading to a gradient that determines the antero-posterior axis.

Opposing gradients of chordin and BMP-4 establish the antero-posterior axis.

Sperm entry leads to a reorganization of the cytoskeleton and redistribution of maternally packaged PAR proteins, which in turn determine the antero-posterior axis.

â-catenin becomes localized to the nucleus in the future anterior cells after fertilization.

. Do Hox genes have a role in the development of C. elegans?

No, C. elegans has Hox genes but none of them are used during development

Yes, C. elegans has 4 clusters of Hox genes, just like mammals, that are required for specification of the identity of structures during embryogenesis

Yes, but only one Hox gene is required in the embryo; the others provide positional identity in the larva

Yes, and their genetic organization and role in development is nearly identical to that in Drosophila

. What are the lin-4 and lin-14 genes of C. elegans?

lin-4 and lin-14 are C. elegans versions of the Hox genes.

lin-4 and lin-14 are genes that are named for their control of the first division, and hence the lineage of the AB and P1 cells.

lin-4 controls the timing of transcription of lin-14, and so is referred to a 'heterochronic' gene.

lin-4 encodes a miRNA that represses lin-14 translation, which in turn regulates timing during larval development.

. Which of these model organisms is closest evolutionarily to humans?

Fruit flies, because of their sophisticated nervous system and the presence of legs.

Plants, because their early divergence from animal lineages means they are closely related to animals, especially humans.

Sea urchins, despite their radial symmetry and lack of limbs.

Worms, despite their few cells, small genomes, and abbreviated complement of Hox genes.

. Which one statement best describes gastrulation in sea urchins?

Gastrulation is initiated by invagination of the micromeres at the vegetal pole.

The mouth of the pluteus larva will form from mesomeres on the oral side of the 60-cell embryo.

The gut will form from the macromeres at the 16-cell stage.

All of the options given are true.

. During early sea urchin development, which embryonic cells have similar organizer activity to that of the amphibian Spemann organizer?

macromeres

mesomeres

micromeres

cells of Veg1 tier

. A classical view of development sees embryos as either 'mosaic' or 'regulative'. Which of the following statements is true?

C. elegans is a mosaic embryo with cell-cell interactions whereas sea urchin embryos are regulative

C. elegans and sea urchin embryos are regulative

C. elegans is a regulative embryo whereas sea urchin is mosaic
incorrect

C. elegans is a strictly mosaic embryo whereas sea urchin is regulative

. In which way is the organizer region in the sea urchin similar to that of frogs?

It accumulates â-catenin, which in turn activates the expression of cell-cell signaling molecules.

It forms near the dorsal lip of the blastopore.

It induces the dorso-ventral axis.

It will express high levels of Nodal.

. In the sea urchin embryo, the function of BMP and Nodal is

to establish the animal-vegetal axis

to specify mesoderm

to control the early patterns of cell division

to organize the oral-aboral axis

. Which of the following statements explains why gain-of-function mutation of Pmar1 results in a vegetalized embryo:

Beta-catenin is at highest concentration in the micromeres

Pmar1 is activated by maternal beta-catenin and Otx

HesC transcription is repressed; skeletogenic genes are activated in all cells

HesC is activated; Delta protein induces mesodermal specification

Chapter 6 Self-test questions

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