Student Reader

Developmental biology studies

1a Describe how you would identify most of the genes required or head development in Drosophila. (1 sentence)

Using a genetic screen for head development mutants followed by linkage analysis of these mutants to pinpoint mutated genes.

1c You want to identify the regulatory elements that allow expression of headless at the anterior terminus. What experiment would you do to find these elements?

Incomplete: 1) Isolated the gene using hybridization to pinpoint it on a gel. 2) Digest the gene. 3) Engineer a construct that fuses these digested segments to a promoter. 4) Observe which gene segment creates a marker expression pattern identical to headless using transformed eggs.

2a You discovered a new organism living in the inverted fountain. You want to know if its early embryogenesis is programmed by maternal mRNA. Describe an experiment you would do to investigate whether maternal mRNA is involved in the development of this organism and the result that would suggest maternal mRNA is involved. (2-4 sentences)

1) Enucleate a mature egg via conjugation. 2) Fertilize both the enucleated egg and a nucleated egg. 3a) Enucleated: If you observe that development continues only until a certain stage, then maternal mRNA is at hand. If development proceeds normally like a nucleated egg, then maternal mRNA is not involved in development. 3b) Nucleated: observe whether development proceeds normally. It should, because this is your control.

2b Among the genes that you discovered as maternal, you want to know whether they act as morphogens. Define a morphogen.

A morphogen is a substance whose activity is dependent on its concentration gradient. Different concentrations of a morphogen will have different effects.

2c Describe an experiment that you would do to test whether a gene acts as a morphogen. Be sure to give the expected outcome.

1) First make sure the substance even forms a gradient. Use antibody staining. (In situ hybridization checks mRNA, but we are analyzing protein.) 2) Identify whether genes downstream of it are expressed only in certain areas: the high, intermediate and low concentration areas of the putative morphogen. 3) Observe whether higher intermediate or low putative morphogen concentrations really do alter downstream expression of genes.

3 Briefly explain the role of gurken and torpedo in patterning the Drosophila embryo.

4a List three important consequences of cleavage in the early embryo.

4b Define autocrine signaling as we discussed it in class. Explain how this mechanism can establish differences in initially identical cells in the early embryo.

5 Toll encodes a receptor that is required for patterning the dorsal-ventral axis. Embryos from mothers that carry a loss of function mutation in Toll were isolated. Draw in the expected expression of twist and drop mRNA in embryos from Toll dominant mutant mothers.

Multiple choice

1

P-granules are found in the oocyte and early embryo of many animals. Which of the following is true?
a)P-granules contain RNA and protein.
b)P-granules are released from vesicles.
c) P-granules contain molecules that act as transcriptional activators.
d) Injection of P-granules into an embryo can cause cells at the site of injection to undergo the mid-blastula transition.
e) P-granules play an essential role in the formation of germ cells in mammals.

2

The slow block to polyspermy is caused by:
a) Depolarization of the egg plasma membrane.
b) The release of cortical granules from the newly fertilized egg.
c) Release of the aerosomal contents by the sperm.
d) Degradation of cytostatic factor.
e) The introduction of the sperm centrosome into the egg.

3

Most maternal determinants in Drosophila embryos are transcription factors because:
a) Signaling molecules are not expressed in the Drosphila oocyte.
b) The cleavage stage embryo is a syncytium.
c) The Drosophila embryo is too small for secreted signals to be able to pattern it.
d) The Drosophila egg shell is impermeable to secreted signals.
e) There are no mechanisms that would allow secreted signals to be localized.

4

The following event is triggered by a rise in intracellular free calcium:
a) Genomic imprinting.
b) The fast block to polyspermy.
c) The cortical reaction.
d) Stabilization of a cytostatic factor.
e) All of the above.

5

What technique would you use to determine whether a rise in intracellular free calcium is required for a development process?
a) Enucleation.
b) Treatment with actinomycin D.
c) Morpholino treatment.
d) Treatment with an ionophore.
e) All of the above.

6

In the fully mature egg immediately prior to fertilization:
a) Protein synthesis is very active.
b) Cortical granules are present.
c) There is no active transcription.
d) Cytostatic factor is present.
e) The egg is surrounded by a protective coating.

[1a 2b 3b 4c 5d 6a]

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