Exam 21: Development of Multicellular Organisms

During branching morphogenesis in lung development, …

Indicate true (T) and false (F) statements below regarding animal development. Your answer would be a four-letter string composed of letters T and F only, e.g. FFFF. ( ) A fertilized egg is totipotent. ( ) Differences in their regulatory DNA can largely explain the differences between animal species. ( ) Inductive signaling is mostly mediated through G-protein-coupled receptors. ( ) A cell's response to a signal depends on its exposure to other signals at that present time as well as in the past.

Indicate whether each of the following groups of genes typically creates a transient pattern in the developing embryo (T) or a long-lived pattern that is preserved (L). Your answer would be a five-letter string composed of letters T and L only, e.g. TTTLT. ( ) Egg-polarity genes ( ) Pair-rule genes ( ) Hox genes ( ) Gap genes ( ) Segment-polarity genes

Indicate whether each of the following proteins is most concentrated near the dorsal (D) or ventral (V) side of the Drosophila embryo. Your answer would be a four-letter string composed of letters D and V only, e.g. DDDV. ( ) Decapentaplegic ( ) Dorsal (nuclear fraction) ( ) Toll (active form) ( ) Twist

Which of the following schematic drawings better depicts the regulatory network that maintains Engrailed (en), Hedgehog (hh), and Wingless (wg) expression following cellularization in a developing Drosophila embryo?

The gene encoding Hes7 in mouse contains three introns. Any or all of these introns can be deleted to alter the delay associated with transcription and splicing of Hes7 mRNA. As a result of such deletions, either the oscillation frequency of this gene's expression can change (result 1) or the oscillatory behavior can disappear altogether (result 2). One of these two results is obtained when only one intron is deleted from the gene, while the other result is obtained when all three introns are removed. Would you expect the oscillation frequency to increase or decrease if result 1 is obtained? Which result (1 or 2) would you expect to observe when all three introns are deleted?

Which of the following is correct regarding neuronal self-avoidance in both invertebrates and vertebrates?

The role of Chordin and Noggin in patterning in developing vertebrates is equivalent to that of …(1) in Drosophila. They are secreted from the …(2) pole and antagonize the activity of bone morphogenetic factors that are secreted throughout the embryo.

Indicate whether each of the following descriptions better applies to patterning by lateral inhibition (L), reaction-diffusion systems (R), or sequential induction (S). Your answer would be a four-letter string composed of letters L, R, and S only, e.g. SSRR. ( ) It does NOT generate asymmetrical patterns from an initial noisy field. ( ) It is based on short-range activation and long-range inhibition. ( ) It can readily generate complex patterns resembling the spots of a leopard or stripes of a zebra. ( ) It is commonly mediated by Notch signaling.

In Drosophila melanogaster, the expression of genes Ultrabithorax and Antennapedia can normally be observed in the third thoracic segment which bears a pair of legs as well as a pair of halteres. Homeotic mutations associated with these two genes can give rise to remarkable disturbances in the organization of the adult fly: two pairs of wings in the case of Ultrabithorax, and legs in the place of antennae in the case of Antennapedia. Would you expect these to be gain-of-function or loss-of-function mutations?

Cactus is a maternal-effect gene coding for an inhibitory protein in the Drosophila Toll signaling pathway that binds to Dorsal in the cytosol and keeps it from nuclear entry. Would you expect maternal loss-of-function mutations in Cactus to give rise to dorsalized or ventralized embryos? What about loss-of-function mutations in Decapentaplegic (Dpp)?

Which cell behavior depicted below is involved in the tube formation that underlies the development of lungs and trachea?

Does the nuclear-to-cytoplasmic ratio increase (I) or decrease (D) during cleavage in early vertebrate development? Would you expect tetraploid embryos to undergo the maternal-zygotic transition earlier (E) or later (L) compared to diploids? If the availability of a transcription regulatory protein determines the timing of this transition, should the protein be a transcriptional activator (A) or repressor (R)? Write down your answer as a three-letter string using the letters in the parentheses above, e.g. IEA.

Consider the embryonic cerebral cortex of a mammal. Near which side of the cortex are the cell bodies of radial glial cells located? To which side of the cortex do the first-born neurons eventually migrate?

Indicate true (T) and false (F) statements below regarding the formation of orderly neural maps in the mammalian brain. Your answer would be a four-letter string composed of letters T and F only, e.g. FFFF. ( ) As a general rule, neurons that fire together avoid each other. ( ) In the tonotopic map of the auditory system, brain neurons are arranged in the auditory cortex according to the pitch of the sound they respond to, like the keys of a piano. ( ) In the optic tectum in the midbrain, brain neurons are arranged along the anterior-posterior axis according to the frequency of light they respond to, like the colors of a rainbow. ( ) If the optic nerve of a frog is cut and the eye is rotated 180° in its socket, the retinal ganglion cells reconnect to their original targets in the optic tectum, therefore creating an inverted map.

Plants and animals use different developmental strategies and have very different ways of life. In which of the following fundamental cellular processes during development are plants most different to animals?

In the following schematic drawing, a growing axon (in red) is extended to a target neuron to form three synapses. In its journey, it is guided by a variety of mechanisms. Sort the following mechanisms to reflect the order in which they guide the navigation of the growth cone toward the target neuron in this example. Ignore the final chemoattraction step toward the target neuron itself. Your answer would be a six-letter string composed of letters A to F only, e.g. FACBDE. (A) Chemoattraction (B) Chemorepulsion (C) Cell surface adhesion (D) Contact inhibition (E) Extracellular matrix adhesion (F) Guidance by pioneer neuron

Which of the following is NOT true regarding vertebrate segmentation?

Sort the following phases in the order that they take place in neural development in vertebrates. Your answer would be a four-letter string composed of letters A to D only, e.g. DACB. (A) Neurons are assigned specific characters according to the place and time of their birth. (B) Neurons form synapses with other neurons or with muscle cells. (C) Synaptic connections are refined and adjusted. (D) Neurons extend axons and dendrites toward their target cells.

The result of Notch-mediated competitive lateral inhibition in a patch of wild-type cells is depicted on the left in the following schematic drawing, in which the black cells have become specialized. Consider a genetic mutation that interferes with intracellular Notch signaling in such a way that Notch can no longer regulate Delta effectively. Which drawing (1 or 2) better represents the outcome with cells bearing this mutation? Do the specialized cells (black hexagons) have active or inactive Notch at their surface?