In the discussion, we have focused on large-scale as well as the inter- and intracellular events that take place during embryogenesis and the formation of adult structures. In particular, we discussed how the adult body plan is laid down by a cascade of gene expression, and the role of cell–cell communication in development. Based on your knowledge of these topics, answer several fundamental questions:

How have we discovered that specific genes control development in an organism like Drosophila?

In the discussion, we have focused on large-scale as well as the inter- and intracellular events that take place during embryogenesis and the formation of adult structures. In particular, we discussed how the adult body plan is laid down by a cascade of gene expression, and the role of cell–cell communication in development. Based on your knowledge of these topics, answer several fundamental questions:

How do we know that molecular gradients in the egg of Drosophila exist?

In the discussion, we have focused on large-scale as well as the inter- and intracellular events that take place during embryogenesis and the formation of adult structures. In particular, we discussed how the adult body plan is laid down by a cascade of gene expression, and the role of cell–cell communication in development. Based on your knowledge of these topics, answer several fundamental questions:

How did we discover that selector genes specify which adult structures will be formed by body segments?

In the discussion, we have focused on large-scale as well as the inter- and intracellular events that take place during embryogenesis and the formation of adult structures. In particular, we discussed how the adult body plan is laid down by a cascade of gene expression, and the role of cell–cell communication in development. Based on your knowledge of these topics, answer several fundamental questions:

How did we learn about the levels of gene regulation involved in vulval development in C. elegans?

In the discussion, we have focused on large-scale as well as the inter- and intracellular events that take place during embryogenesis and the formation of adult structures. In particular, we discussed how the adult body plan is laid down by a cascade of gene expression, and the role of cell–cell communication in development. Based on your knowledge of these topics, answer several fundamental questions:

How do we know that eye formation in all animals is controlled by a binary switch gene?

Write a short essay based on the concepts related to stages of development that outlines the role of differential transcription, gene control of cell fate, and the role of signaling systems in development.

Carefully distinguish between the terms differentiation and determination. Which phenomenon occurs initially during development?

Nuclei from almost any source may be injected into Xenopus oocytes. Studies have shown that these nuclei remain active in transcription and translation. How can such an experimental system be useful in developmental genetic studies?

Distinguish between the syncytial blastoderm stage and the cellular blastoderm stage in Drosophila embryogenesis.

What are maternal-effect genes?

When are gene products from these genes made, and where are they located?

What aspects of development do maternal-effect genes control?

What is the phenotype of maternal-effect mutations?

What are zygotic genes, and when are their gene products made?

What is the phenotype associated with zygotic gene mutations?

Does the maternal genotype contain zygotic genes?

List the main classes of zygotic genes. What is the function of each class of these genes?

Experiments have shown that any nuclei placed in the polar cytoplasm at the posterior pole of the Drosophila egg will differentiate into germ cells. If polar cytoplasm is transplanted into the anterior end of the egg just after fertilization, what will happen to nuclei that migrate into this cytoplasm at the anterior pole?

How can you determine whether a particular gene is being transcribed in different cell types?

You observe that a particular gene is being transcribed during development. How can you tell whether the expression of this gene is under transcriptional or translational control?

The homeotic mutation Antennapedia causes mutant Drosophila to have legs in place of antennae and is a dominant gain-of-function mutation. What are the properties of such mutations? How does the Antennapedia gene change antennae into legs?

The Drosophila homeotic mutation spineless aristapedia (ssᵃ) results in the formation of a miniature tarsal structure (normally part of the leg) on the end of the antenna. What insight is provided by (ssᵃ) concerning the role of genes during determination?

Embryogenesis and oncogenesis (generation of cancer) share a number of features including cell proliferation, apoptosis, cell migration and invasion, formation of new blood vessels, and differential gene activity. Embryonic cells are relatively undifferentiated, and cancer cells appear to be undifferentiated or dedifferentiated. Homeotic gene expression directs early development, and mutant expression leads to loss of the differentiated state or an alternative cell identity. M. T. Lewis [(2000). Breast Can. Res. 2:158–169] suggested that breast cancer may be caused by the altered expression of homeotic genes. When he examined 11 such genes in cancers, 8 were underexpressed while 3 were overexpressed compared with controls. Given what you know about homeotic genes, could they be involved in oncogenesis?

Early development depends on the temporal and spatial interplay between maternally supplied material and mRNA and the onset of zygotic gene expression. Maternally encoded mRNAs must be produced, positioned, and degraded [Surdej and Jacobs-Lorena (1998). Mol. Cell Biol. 18:2892–2900]. For example, transcription of the bicoid gene that determines anterior–posterior polarity in Drosophila is maternal. The mRNA is synthesized in the ovary by nurse cells and then transported to the oocyte, where it localizes to the anterior ends of oocytes. After egg deposition, bicoid mRNA is translated and unstable bicoid protein forms a decreasing concentration gradient from the anterior end of the embryo. At the start of gastrulation, bicoid mRNA has been degraded. Consider two models to explain the degradation of bicoid mRNA: (1) degradation may result from signals within the mRNA (intrinsic model), or (2) degradation may result from the mRNA's position within the egg (extrinsic model). Experimentally, how could one distinguish between these two models?

Formation of germ cells in Drosophila and many other embryos is dependent on their position in the embryo and their exposure to localized cytoplasmic determinants. Nuclei exposed to cytoplasm in the posterior end of Drosophila eggs (the pole plasm) form cells that develop into germ cells under the direction of maternally derived components. R. Amikura et al. [(2001). Proc. Nat. Acad. Sci. (USA) 98:9133–9138] consistently found mitochondria-type ribosomes outside mitochondria in the germ plasma of Drosophila embryos and postulated that they are intimately related to germ-cell specification. If you were studying this phenomenon, what would you want to know about the activity of these ribosomes?

One of the most interesting aspects of early development is the remodeling of the cell cycle from rapid cell divisions, apparently lacking G1 and G2 phases, to slower cell cycles with measurable G1 and G2 phases and checkpoints. During this remodeling, maternal mRNAs that specify cyclins are deadenylated, and zygotic genes are activated to produce cyclins. Audic et al. [(2001). Mol. and Cell. Biol. 21:1662–1671] suggest that deadenylation requires transcription of zygotic genes. Present a diagram that captures the significant features of these findings.

A number of genes that control expression of Hox genes in Drosophila have been identified. One of these homozygous mutants is extra sex combs, where some of the head and all of the thorax and abdominal segments develop as the last abdominal segment. In other words, all affected segments develop as posterior segments. What does this phenotype tell you about which set of Hox genes is controlled by the extra sex combs gene?

The apterous gene in Drosophila encodes a protein required for wing patterning and growth. It is also known to function in nerve development, fertility, and viability. When human and mouse genes whose protein products closely resemble apterous were used to generate transgenic Drosophila [Rincon-Limas et al. (1999). Proc. Nat. Acad. Sci. (USA) 96:2165–2170], the apterous mutant phenotype was rescued. In addition, the whole-body expression patterns in the transgenic Drosophila were similar to normal apterous.

What is meant by the term rescued in this context?

The apterous gene in Drosophila encodes a protein required for wing patterning and growth. It is also known to function in nerve development, fertility, and viability. When human and mouse genes whose protein products closely resemble apterous were used to generate transgenic Drosophila [Rincon-Limas et al. (1999). Proc. Nat. Acad. Sci. (USA) 96:2165–2170], the apterous mutant phenotype was rescued. In addition, the whole-body expression patterns in the transgenic Drosophila were similar to normal apterous.

What do these results indicate about the molecular nature of development?

In Arabidopsis, flower development is controlled by sets of homeotic genes. How many classes of these genes are there, and what structures are formed by their individual and combined expression?