Chapter 21

Where is bicoid mRNA translated? Nurse cells Sperm cells Follicle cells Fertilized egg

Fertilized egg bicoid mRNA is translated at the anterior pole of the fertilized egg.

The region of a Drosophila embryo with the highest concentration of bicoid protein will develop into the _____. head ovaries vulva homeobox abdomen

Head The head develops where there is a high concentration of bicoid protein.

True or False? Pattern formation refers to events that organize embryonic cells in space True False

True Pattern formation is the process by which the location of an embryo's body segments is determined.

The bicoid gene is a type of _____ gene. segmentation pair-rule segment-polarity egg-polarity gap

egg-polarity Egg-polarity genes are responsible for establishing the polarity of the egg.

Outline the general steps of differential gene expression induced by concentration-dependent morphogens.

1) A cell or cells synthesize and release the morphogen or signaling molecule. 2) The distribution of morphogen establishes an extracellular concentration gradient. 3) The morphogen binds receptors on the surface of other cells. The percent occupancy of morphogen decreases as the distance increases between the source cell and the receptor cell. 4) Through a signaling pathway, activated receptor leads to an increase in expression of a transcriptional regulator that controls expression of many genes.

The evolution of arthropod body plans includes incidents of all of the following except A) changes in homeotic gene order B) changes in protein function C) changes in transcript expression D) changes in downstream targets of the same genes

A

Which body part develops in regions with a low concentration of Bicoid protein? Thorax Head Abdomen

Abdomen The regions with low concentrations of Bicoid protein develop into posterior structures such as the abdomen.

Name the relevant mRNA or protein used in cell to cell contact. σF SpoIIR pro-σE σE All of the above.

All of them

Which of the following is not a body segment of the fruit fly embryo? Thorax Abdomen Antenna Head

Antenna

The ability of two cells to respond differently to a morphogen depends on A) The concentration of the morphogen B) The number of receptors occupied/triggered by the morphogen C) The affinity of the resulting transcription factors/activators/repressors for their binding sites in given gene promoters. D) A, B, C E) A, B

D) all of them

Which of the following statements concerning the expression (or lack of expression) of the Ubx gene in development is NOT true? Ubx proteins in insects are functionally different than Ubx proteins found in crustaceans. Lack of Ubx expression in the first thoracic segment (T1) during the early development of isopods leads to the formation of modified limbs called maxillipeds in T1. Expression of Ubx in the mesothorax (due to the Cbx mutation) during the early development of fly embryos leads to "wingless" adults (having two pairs of halteres). Expression of Ubx represses expression of DII genes in the abdominal segments of crustaceans and the formation of thoracic limbs.

Expression of Ubx represses expression of DII genes in the abdominal segments of crustaceans and the formation of thoracic limbs. Expression of Ubx in the abdominal segments of insects does repress the DII genes and prevents formation of thoracic limbs. In contrast, expression of Ubx does not repress DII expression in the abdominal segments of crustaceans. The explanation for this is that the Ubx proteins produced by insects are functionally different than the Ubx proteins found in crustaceans. The crustacean Ubx protein has a short motif consisting of 29 amino acid residues. This "anti-repression" motif prevents Ubx from repressing DII; if this motif is deleted from the crustacean Ubx, then these crustacean proteins can repress DII activity as effectively as the fly Ubx proteins. Similarly, if this motif is attached to a fly Ubx protein, then fly Ubx no longer represses DII.

Which of the following statements about a gene that shows maternal effect inheritance is true? Offspring will have a mutant phenotype if the father has a mutant genotype. Offspring will show a mutant phenotype if the mother has a mutant genotype. Embryonic cells transcribe the gene. Offspring will always show a mutant phenotype if they have a mutant genotype.

Offspring will show a mutant phenotype if the mother has a mutant genotype. This statement is true; the gene is transcribed in the mother, and the mRNA is delivered to the zygote.

Describe an experiment that showed that the 3′ UTR of bicoid and oskar mRNAs is required for proper localization in the Drosophila oocyte.

a. Researchers engineered an mRNA that had the 3' UTR of OSKAR mRNA replaced with the 3' UTR from BICOID mRNA. b. They observed OSKAR mRNA localization in the anterior pole as normally observed for BICOID mRNA normally. This is enough to induce pole cell formation at the wrong locations.

Which of the following statements about pattern formation are true? Select the four statements that are true. Differential gene expression affects the developmental process in animals. Pattern formation begins in adult animals. Positional information controls pattern formation. Homeotic genes establish major body axes. The process of pattern formation involves segmentation of the body but does not involve the development of segment-specific body parts. Homeotic genes code for transcription factors that control the development of segment-specific body parts. Cells receive molecular signals that communicate their position in relation to other cells.

Differential gene expression affects the developmental process in animals. Positional information controls pattern formation. Homeotic genes code for transcription factors that control the development of segment-specific body parts. Cells receive molecular signals that communicate their position in relation to other cells. Pattern formation is the development of a multicellular organism's spatial organization, including the arrangement of tissues and organs. Cells receive molecular signals, collectively called positional information, that inform the cells about their location in relation to other cells and to the body axes. Positional information regulates pattern formation. Homeotic genes are regulatory genes that work after the body axes have been established. Homeotic genes identify particular body segments in an individual, eventually leading to the formation of segment-specific body structures in the correct locations on the body.

Define differential gene expression in the context of development. Differential gene expression is the synthesis of a protein or non-coding RNA in a subset of non-embryonic cells. Differential gene expression is the regulation of a protein or non-coding RNA in a subset of non-embryonic cells. Differential gene expression is the synthesis of a protein or non-coding RNA in a subset of embryonic cells. Differential gene expression is the regulation of a protein or non-coding RNA in a subset of embryonic cells.

Differential gene expression is the synthesis of a protein or non-coding RNA in a subset of embryonic cells.

Maternal effect genes are transcribed in the egg after fertilization. True False

False Correct. Maternal effect genes are transcribed during oogenesis (in the mother). The mRNA is translated in the embryo after fertilization.

Bicoid mRNA is translated in _____. Sertoli cells the fertilized egg sperm cells chimera cells nurse cells

the fertilized egg BicoidmRNA is translated in the fertilized egg.

Which of the following statements about the development of an early Drosophila embryo is NOT true? Dorsal protein activates Twist expression in the ventral neurogenic ectoderm regions of the embryo. Dorsal protein activates rhomboid expression only in the ventral neurogenic ectoderm region. rhomboid and sog both have enhancers containing binding sites for Snail protein but twist does not. Dorsal protein activates sog expression only in the ventral and lateral neurogenic ectoderm regions.

Dorsal protein activates Twist expression in the ventral neurogenic ectoderm regions of the embryo. In the early developing Drosophila embryo, a concentration gradient of the morphogen Dorsal protein is established with the highest concentration in the ventral region and lowest in the dorsal region of the embryo. One of the gene targets of Dorsal is twist, which has two low-affinity Dorsal-binding sites that can be occupied only by peak levels of the Dorsal gradient. This means that twist is only expressed in the ventralmost 18 cells, which will form the mesoderm of the embryo. twist cannot be expressed in what will become neurogenic ectoderm regions because the concentration of Dorsal protein is too low.

A set of known mutations in the BX-C genes in Drosophila results in the development of wings on a body segment that would not ordinarily have wings. This is an example of mutation in which class of developmental genes? Homeotic genes Lethal genes Maternal effect genes Segmentation genes

Homeotic genes Correct. Homeotic genes specify segment identity with respect to the body part that will develop at metamorphosis.

Which of the following is NOT true concerning the formation of the eve stripe 2 during Drosophila embryogenesis? Giant protein creates the anterior border of the eve stripe 2. An anteroposterior gradient of Bicoid protein activates transcription of eve. Knirps protein creates the posterior border of the eve stripe 2. An anteroposterior gradient of Hunchback protein activates transcription of eve.

Knirps protein creates the posterior border of the eve stripe 2. Even-skipped or eve for short is a "pair-rule" gene that is expressed in a series of seven alternating stripes that extend along the length of the embryo. The second eve stripe is created by the interplay among two transcriptional activators (Bicoid and Hunchback) and two transcriptional repressors (Giant and Krüppel). Binding sites for all four of these proteins are found on one of the two 5′ enhancers upstream of the eve gene. The high concentration of Bicoid and Hunchback at the anterior end of the embryo activates eve, whereas repression by Giant and Krüppel in specific regions of the embryo create the anterior and posterior borders of stripe-2, respectively. The repressors Giant and Krüppel are known as "gap proteins." Knirps, another gap protein, is involved in creating other eve stripes.

Which of the following are signaling proteins that stimulate the proteolytic processing of intracellular proteins important for transcription activation? SpoIIR and Shh Shh and Delta Macho-1 and Shh SpoIIR and Delta

SpoIIR and Delta In the bacterium Bacillus subtilis, spore formation begins when a forespore cell produces a signaling protein called SpoIIR. SpoIIR then travels to the septum separating the forespore cell from the mother cell where it triggers the proteolytic activation of an inactive form of σE called "pro-σE" found in the mother cell. The activated σE subunits then help initiate transcription of specific genes in the mother cell. In the early development of insects, a neuroblast (precursor cell to a neuron) secretes signaling molecules called Delta. These secreted molecules bind to Notch receptors on the surfaces of neighboring cells in the neurogenic ectoderm. Upon activation, the intracellular domain of Notch is cleaved by intracellular proteases. Cleavage produces a molecular subunit called NotchIC, which then travels to the nucleus where it associates with a DNA-binding protein called Su(H). The NotchIC-Su(H) complex activates genes that encode transcriptional repressors that prevent the cell from becoming a neuron. This developmental mechanism prevents cells in physical contact with a neuroblast from developing into neurons themselves and instead they become skin cells.

Which of the following statements about the Bicoid protein is true? The Bicoid protein is a regulatory transcription factor. The Bicoid protein establishes the dorsal-ventral body axis. The Bicoid protein is diffused evenly throughout the fertilized egg. The Bicoid protein is a cytoplasmic determinant.

The Bicoid protein is a regulatory transcription factor. The Bicoid protein regulates expression of the embryo's early developmental genes.

Which of the following statements concerning the localization of Ash1 mRNAs in the yeast Saccharomyces cerevisiae is true? The 3′ UTR region of Ash1 protein binds directly to myosin, which is attached to the polarized actin filament. Following budding, the mother cell is unable to express the HO gene. The transfer of Ash1 mRNA from the mother cell to the daughter cell occurs via transport along a growing actin filament in a (+) to (-) direction. The daughter cell cannot change its mating type.

The daughter cell cannot change its mating type. A mother cell and its daughter cell can show different mating types. Although both mother and daughter cells might initially, for example, exhibit the "a" mating type, only the mother is capable of switching to the "α" mating type. The mother is able to switch mating types because the HO gene, which controls switching, can be activated in the mother because of the absence of Ash1 repressor protein, whereas HO in the daughter is repressed by Ash1. Ash1 mRNAs transcribed in the nucleus of the mother cell before budding become localized in the daughter cell during the budding process because of cytoskeletal-mediated transport of Ash1 mRNAs from mother cell to daughter cell.

If bicoid mRNA is injected at the anterior end of an egg from a bicoid mutant mother, what would the phenotype of the resulting larva be? The larva would be normal with one head at the posterior pole. The larva would have two heads, one at the anterior pole and one in the middle of its body. The larva would have a head at each pole of its body. The larva would be normal with one head at the anterior pole.

The larva would be normal with one head at the anterior pole. The injected mRNA would rescue the mutant phenotype of the egg.

Which of the following is an accurate description of synteny? two genes found in two different genomes that are homologous to each other the total number of genes found in a genome the study of how developmental processes have evolved a block of genes linked together on the same chromosome that is conserved between distantly related animals

a block of genes linked together on the same chromosome that is conserved between distantly related animals Comparative genome analysis has revealed that distantly related animals share conserved blocks of linked genes (show a high degree of synteny). Even organisms that have not had a common ancestor for hundreds of millions of years can exhibit some synteny.

The region of a Drosophila embryo with a low concentration of bicoid protein will develop into the _____. abdomen male flowers thorax head female flowers

abdomen The abdomen develops where there is a low concentration of bicoid protein.

Which strategy for differential gene expression do Bacillus subtilis cells use when the forespore influences gene expression in the mother cell? the localization of ash1 mRNAs to the daughter cell cell-to-cell contact the localization of HO genes to the daughter cell None of the above.

cell-to-cell contact

What process produces the gradient of bicoid protein in a fertilized egg? exocytosis phagocytosis diffusion pinocytosis receptor-mediated endocytosis

diffusion Bicoid protein is produced at the anterior end and diffuses toward theposterior, resulting in a gradient.

What triggers the translation of bicoid mRNA? formation of the right-left axis of the developing embryo fertilization of the egg apoptosis capacitation of sperm formation of the anterior-posterior axis of the developing embryo

fertilization of the egg Fertilization of the egg triggers translation of bicoid mRNA.

Which of the following can regulate gene expression during development, but does NOT represent a pathway of cell-to-cell signal transduction or establishment of an extracellular gradient? A ligand binding to a cell surface receptor triggers release of DNA-binding proteins. mRNA localization morphogen secretion by a cluster of cells A ligand binding to a cell surface receptor triggers phosphorylation of DNA-binding proteins.

mRNA localization Correct Three strategies have evolved for instructing cells to express specific genes during development: cell-to-cell contact, signaling through the diffusion of a secreted signaling molecule (morphogen), and localization of maternal mRNAs in an egg (either before or after fertilization). Only the third listed process—mRNA localization—does not represent a pathway of cell-to-cell signal transduction or establishment of an extracellular gradient for regulating gene expression. Localization of mRNAs allows cells to distribute critical regulatory molecules asymmetrically to specific parts of a cell, typically via transport along elements of the cytoskeleton.

The bicoid gene is transcribed by _____. a sperm cell the zygote the acrosome nurse cells embryonic cells

nurse cells

The bicoid gene product is directly responsible for _____ in a developing Drosophila embryo. the establishment of the right-left axis vulval development flower development the establishment of the anterior-posterior axis apoptosis

the establishment of the anterior-posterior axis The concentration gradient of bicoid protein determines the anterior-posterior axis of a developing Drosophila.

Which strategy for differential gene expression do Saccharomyces cerevisiae cells use in the regulation of mating-type switching? None of the above. cell-to-cell contact the localization of HO genes to the daughter cell the localization of ash1 mRNAs to the daughter cell

the localization of ash1 mRNAs to the daughter cell

In Drosophila development, the effects of BICOID protein vary along the axis of the embryo. This is because _______. there is an anterior to posterior gradient in BICOID protein concentration in the embryo BICOID is a transcription factor BICOID both activates and represses gene activity BICOID mRNA exists in the egg prior to fertilization

there is an anterior to posterior gradient in BICOID protein concentration in the embryo Correct. After fertilization, BICOID mRNA is translated and a concentration gradient of BICOID protein forms along the anterior-posterior axis of the embryo.

A high concentration of bicoid protein at the opposite ends of a developing Drosophila embryo would result in the development of a _____. two-headed fly fly with a head growing out of its abdomen fly with two abdomens hermaphrodite fly with legs growing out of its head

two-headed fly The head develops where there is a high concentration of bicoid protein.