Lorna 356 Lectures 5,6,7

1. In the early gastrula, how many tissues have their fate determined?

Two - the ventral side

None of the tissues

Three - the lateral edges

One- the dorsal lip

In the early gastrula stage, it is the dorsal lip that plays a critical role in determining the fate of one of the tissues. The ventral side, lateral edges, and other tissues do not have their fate determined at this stage.

Explanation

In the early gastrula stage, it is the dorsal lip that plays a critical role in determining the fate of one of the tissues. The ventral side, lateral edges, and other tissues do not have their fate determined at this stage.

2. What happens to newt embryos when the zygote is constricted in the plane of the first cleavage according to re Spemann?

At the 16 cell stage a nucleus from one side escapes to the nuclear free half, and then proceeds to begin cleavage divisions on this second side. Eventually, two normal embryos form.

Newt embryos fail to divide and remain as a single cell.

The newt embryos form abnormally large cells at the site of constriction.

The zygote stops development completely.

When the zygote is constricted in the plane of the first cleavage according to re Spemann, a nucleus from one side escapes to the nuclear free half and leads to the formation of two normal embryos through cleavage divisions.

Explanation

When the zygote is constricted in the plane of the first cleavage according to re Spemann, a nucleus from one side escapes to the nuclear free half and leads to the formation of two normal embryos through cleavage divisions.

3. During re Spemann's constriction along the plane of first cleavage, what was the significance of the observation?

It showed that the early amphibian nuclei have different genetic material.

That the early amphibian nuclei are the same, and that each is capalbeof forming an entire embryo.

It demonstrated that only one nucleus is sufficient for embryonic development in amphibians.

It indicated a lack of nucleus interaction during the early stages of embryonic development.

Re Spemann's constriction along the plane of first cleavage plays a critical role in demonstrating the developmental potential of each early amphibian nucleus, showcasing that each nucleus is capable of giving rise to an entire embryo.

Explanation

Re Spemann's constriction along the plane of first cleavage plays a critical role in demonstrating the developmental potential of each early amphibian nucleus, showcasing that each nucleus is capable of giving rise to an entire embryo.

4. What happens when the grey crescent is localized in only one of the two blastomeres after the zygote is constricted perpendicular to the plane of first cleavage?

The blastomere without the grey crescent develops normally, contributing to the formation of dorsal structures.

The blastomere with the grey crescent undergoes abnormal differentiation, resulting in the formation of dorsal structures.

Abnormal differentiation of the blastomere which does not recieve the grey crescent. Ectoderm, mesoderm and endoderm are still present but no dorsal structures are, leading spemann to term this mass of cells the "belly piece"

Normal development of both blastomeres occurs, leading to the formation of dorsal structures.

The correct answer describes the consequences of the grey crescent being localized in only one of the blastomeres. The incorrect answers either incorrectly posit normal development or misinterpret the impact on dorsal structures.

Explanation

The correct answer describes the consequences of the grey crescent being localized in only one of the blastomeres. The incorrect answers either incorrectly posit normal development or misinterpret the impact on dorsal structures.

5. What structure does the grey crescent lead to and what function does this structure have in gastrulation?

Ventral lip, responsible for ectoderm differentiation in gastrulation

Central lip, involved in neurulation during gastrulation

Lateral lip, generates the mesoderm layer in gastrulation

Dorsal lip, committed to invaginate the blastule (and thus initiate gastrulation i think)

The grey crescent in gastrulation leads to the dorsal lip, which is committed to invaginate the blastula, thus initiating gastrulation. The incorrect answers provided are not accurate descriptions of the grey crescent and its role in gastrulation.

Explanation

The grey crescent in gastrulation leads to the dorsal lip, which is committed to invaginate the blastula, thus initiating gastrulation. The incorrect answers provided are not accurate descriptions of the grey crescent and its role in gastrulation.

6. What creates the Nieuwkoop center?

The Nieuwkoop center is created by the activation of specific genes in the embryo.

He Nieuwkoop center is created by the cytoplasmic rotation that occurs during fertilization (see Chapter 7).When this rotation is inhibited by UV light, the resulting embryo willnot form dorsal-anterior structures such as the head or neural tube

The Nieuwkoop center is created by the formation of the blastula during development.

The Nieuwkoop center is created by the differentiation of neural crest cells in the embryo.

The Nieuwkoop center is a critical developmental organizer that is created by the cytoplasmic rotation during fertilization, which is crucial for the formation of dorsal-anterior structures in the embryo. This process is distinct from the other options provided.

Explanation

The Nieuwkoop center is a critical developmental organizer that is created by the cytoplasmic rotation during fertilization, which is crucial for the formation of dorsal-anterior structures in the embryo. This process is distinct from the other options provided.

7. What is the product of the Xbra (brachyury) gene?

The Xbra protein is a transcription factor that activates the genes that produce mesoderm-specific proteins.

The Xbra gene is responsible for producing neurotransmitters in the brain.

The Xbra gene encodes a structural protein that forms the cytoskeleton of the cell.

The Xbra gene codes for a hormone that regulates blood sugar levels.

The correct answer describes the role of the Xbra protein as a transcription factor in activating genes that produce mesoderm-specific proteins, which is essential in early embryonic development.

Explanation

The correct answer describes the role of the Xbra protein as a transcription factor in activating genes that produce mesoderm-specific proteins, which is essential in early embryonic development.

8. What induces cells overlying the vegetal cells to begin expressing the transcription factor Xbra (brachyury) which specifies mesodermal change by activating genes that produce mesoderm specific proteins?

The transcription factor Xbra directly activates genes that produce mesoderm specific proteins

Vegetal cells produce activin and Nodal proteins

Cells in the animal region secrete Vg1 and VegT

Vegetalcells secrete TGFbeta like factors such as Vg1and VegT, a transcriptionfactor that instructs the endoderm to secrete activinand Nodal proteins (all TGF-b family members).

Vegetal cells secrete TGFbeta like factors such as Vg1 and VegT, which play a crucial role in inducing the expression of Xbra by cells overlying the vegetal cells. This process is essential for specifying mesodermal change in the developing embryo.

Explanation

Vegetal cells secrete TGFbeta like factors such as Vg1 and VegT, which play a crucial role in inducing the expression of Xbra by cells overlying the vegetal cells. This process is essential for specifying mesodermal change in the developing embryo.

9. How do Spemann organiser cells determine their dorsal position?

The beta catenin signal and the nieuwkoop center signals.

A. The Notch signaling pathway activation.

B. The Wnt pathway inhibition.

C. The Sonic Hedgehog pathway activation.

Spemann organiser cells determine their dorsal position through interactions involving the beta catenin signal and the nieuwkoop center signals, not through the Notch, Wnt, or Sonic Hedgehog pathways.

Explanation

Spemann organiser cells determine their dorsal position through interactions involving the beta catenin signal and the nieuwkoop center signals, not through the Notch, Wnt, or Sonic Hedgehog pathways.

10. Where does Beta-catenin accumulate during early embryo development in xenopus?

Beta-catenin accumulates in the tail region of the xenopus embryo during early cleavage

Beta-catenin accumulates randomly throughout the xenopus embryo during early development

?-catenin continues to accumulate preferentially at the dorsal sidethroughout early cleavage, and this accumulation is seen in the nucleiof the dorsal cells ; Schneider et al. 1996; Larabell et al. 1997).This region of ?-catenin accumulation originally appears to cover boththe Nieuwkoop center and organizer regions. During later cleavage, thecells containing ?-catenin may reside specifically in the Nieuwkoopcenter (Heasman et al. 1994a; Guger and Gumbiner 1995).

Beta-catenin accumulates at the ventral side during early cleavage

Explanation for the correct answer and why the incorrect answers are not accurate

Explanation

Explanation for the correct answer and why the incorrect answers are not accurate

11. What is beta catenin required for?

?-catenin is necessary for forming the dorsal axis, since experimentaldepletion of ?-catenin transcripts with antisense oligonucleotidesresults in the lack of dorsal structures

Beta catenin is essential for regulating blood sugar levels in the body.

Beta catenin is necessary for synthesizing vitamin D in the skin.

Beta catenin is required for protein digestion in the stomach.

Beta catenin plays a crucial role in embryonic development by forming the dorsal axis, as confirmed by experiments using antisense oligonucleotides to deplete beta catenin transcripts. This process leads to the absence of dorsal structures, highlighting the significance of beta catenin in this biological context.

Explanation

Beta catenin plays a crucial role in embryonic development by forming the dorsal axis, as confirmed by experiments using antisense oligonucleotides to deplete beta catenin transcripts. This process leads to the absence of dorsal structures, highlighting the significance of beta catenin in this biological context.

12. What happens when exogenous ?-catenin is injected into the ventral side of the developing embryo?

The ventral side of the embryo becomes translucent.

The embryo stops developing completely.

The injection of exogenous ?-catenin into the ventral side of the embryo produces a secondary axis. ?-catenin is part of the Wnt signal transduction pathway and is negatively regulated by the glycogen synthase kinase 3

The dorsal side of the embryo becomes enlarged.

When exogenous ?-catenin is injected into the ventral side of the developing embryo, it leads to the formation of a secondary axis due to its role in the Wnt signal transduction pathway.

Explanation

When exogenous ?-catenin is injected into the ventral side of the developing embryo, it leads to the formation of a secondary axis due to its role in the Wnt signal transduction pathway.

13. What molecular mechanisms lead to the expression of Beta catenin in the dorsal, but not the ventral, parts of the developing embryo?

Beta catenin is actively transported to the dorsal side of the embryo by a specific transporter protein.

Dorsal and ventral parts of the embryo have different concentrations of receptors that bind to Beta catenin and activate its expression.

The ventral part of the embryo synthesizes a protein that inhibits the degradation of Beta catenin by the GSK-3+axin+APC complex.

GSK-3+axin+APC complex binds Beta catenin )(armadillo) and degrades it via phosphorylation. However, dorsally, Dishevelled binds GSK-3, allowing beta catenin to accumulate.

The correct mechanism involves the regulation of Beta catenin by the GSK-3+axin+APC complex and Dishevelled, rather than active transport, an inhibitory protein, or differential receptor binding.

Explanation

The correct mechanism involves the regulation of Beta catenin by the GSK-3+axin+APC complex and Dishevelled, rather than active transport, an inhibitory protein, or differential receptor binding.

14. What is the movement of Dishevelled protein following fertilisation?

Dishevelled protein moves to the ventral side of the embryo following fertilisation.

Dishevelled protein is released into the surrounding environment upon fertilisation.

Dishevelled protein remains in the vegetal cortex of the fertilised egg.

1)Dishevelled protein is initiallyfound in the vegetal cortex of the unfertilisedegg.2)Upon fertilisation, cortical rotationoccurs and Dsh is translocated along the microtubular array to the dorsalside of the embryo3)Thus there is adorsal enrichment of Dsh protein

Upon fertilisation, cortical rotation causes Dishevelled protein to move along the microtubular array to the dorsal side of the embryo, leading to its dorsal enrichment.

Explanation

Upon fertilisation, cortical rotation causes Dishevelled protein to move along the microtubular array to the dorsal side of the embryo, leading to its dorsal enrichment.

15. What happens if the siamois gene is ectopically expressed in the ventral vegetal cells?

The cells differentiate into muscle cells.

Asecondary axis emerges. In addition, if cortical rotation is inhibited, siamois expression iseliminated. Siamois is a homeodomain transcription factorand it is expressed in the Niewkoop centre.

The cells undergo apoptosis.

There is no effect on the development of the embryo.

16. What is the relationship of TCF-3 and armadillo to siamois?

TCF-3is thought to sit on the promoter of the siamoisgene and repress its transcription in the ventral cells. In the dorsal cells,beta-catenin is activated andcomplexes with TCF3 proteins. This lifts the repression of siamois, siamois is activated and Siamois protein is produced. Siamois protein then bindsto and activates the promoters of several genes involved in organizer function. Siamois and Xlim 1 see cb p25

Armadillo represses siamois gene in dorsal cells.

TCF-3 activates transcription of siamois in ventral cells.

Beta-catenin is not involved in the regulation of siamois gene.

TCF-3 acts as a repressor of siamois gene transcription in ventral cells, while beta-catenin plays a role in activating the gene in dorsal cells. Armadillo is not mentioned in the context of siamois regulation.

Explanation

TCF-3 acts as a repressor of siamois gene transcription in ventral cells, while beta-catenin plays a role in activating the gene in dorsal cells. Armadillo is not mentioned in the context of siamois regulation.

17. What is the role of goosecoid when it complexes with siamois?

The top two embryos, injected with goosecoid mRNA, show two dorsal axes, the bottom control embryos only show one

Injection of goosecoid mRNA into ventral vegetal cells induces the formation of another blastopore lip

A control embryo at the gastrula stage has one dorsal blastopore lip (arrow)

Goosecoid is essential foractivating numerous genes in the organizer.A)A control embryo atthe gastrula stage has one dorsal blastoporelip (arrow)B)Injection of goosecoid mRNA into ventralvegetal cells induces the formation of another blastopore lipC)The top two embryos,injected with goosecoid mRNA, show twodorsal axes, the bottom control embryos only show oneD)Two complete sets ofhead structures are induced by goosecoid mRNA injection

When siamois complexes with goosecoid, goosecoid plays a crucial role in activating a variety of genes in the organizer region, influencing the development of the embryo. The incorrect answers provided do not accurately describe the specific role of goosecoid in this context.

Explanation

When siamois complexes with goosecoid, goosecoid plays a crucial role in activating a variety of genes in the organizer region, influencing the development of the embryo. The incorrect answers provided do not accurately describe the specific role of goosecoid in this context.

18. What did the nieuwkoop early experiments reveal about the mesoderm inducing properties of the vegetal endoderm?

The nieuwkoop early experiments showed that the vegetal endoderm had no role in mesoderm induction at all.

TheNieuwkoop early experimentsshowed that the vegetal endoderm was not just a homogeneous mass of cells, butthat the dorsal and ventral vegetal cells had differing features. In mesoderminduction experiments, ventral vegetal cells, when combined with animal cap cells,could induce ventral mesoderm (like mesenchyme,blood, muscle, kidney) and dorsal vegetal cells could induce dorsal mesoderm(like somites, notochord). Thissuggested that different factors, or different CONCENTRATIONS of the samefactor, were being secreted depending whether the vegetal cells were ventral ordorsal (Niewkoop centre).

The nieuwkoop early experiments suggested that only the animal cap cells were responsible for mesoderm induction and not the vegetal endoderm.

The nieuwkoop early experiments revealed that the vegetal endoderm has uniform properties which can induce both ventral and dorsal mesoderm in equal measure.

19. What is the result of high levels of Xnr in the endoderm?

Lack of organiser formation, high BMP4, high Xwnt8.

Organiser formation, low BMP4, low Xwnt8

Increased organiser formation, low BMP4, high Xwnt8.

Decreased organiser formation, high BMP4, low Xwnt8.

High levels of Xnr in the endoderm typically lead to the formation of the organiser, as well as low levels of BMP4 and Xwnt8. The incorrect answers provided showcase different combinations of outcomes that do not align with the known effects of high Xnr levels in the endoderm.

Explanation

High levels of Xnr in the endoderm typically lead to the formation of the organiser, as well as low levels of BMP4 and Xwnt8. The incorrect answers provided showcase different combinations of outcomes that do not align with the known effects of high Xnr levels in the endoderm.

20. What does low levels of Xnr in the endoderm lead to?

Decreased Xnt8 and BMP4 levels, leading to endoderm formation.

Upregulation of Xnr, resulting in ectoderm differentiation.

High Xnt8 and BMP4, leads to ventral mesoderm formation.

Increased Xnr levels, leading to dorsal mesoderm formation.

Low levels of Xnr in the endoderm lead to an upregulation of High Xnt8 and BMP4, which in turn promotes ventral mesoderm formation.

Explanation

Low levels of Xnr in the endoderm lead to an upregulation of High Xnt8 and BMP4, which in turn promotes ventral mesoderm formation.

21. What gene is activated by the complex between Arm and TCF? What type of complex is this?

APC

Siamois, Arm and TCF are a transcription factor complex.

Axin

Wnt3

The correct answer refers to the transcription factor complex between Arm and TCF that activates the Siamois gene. The incorrect answers are other components of the Wnt signaling pathway, but they do not form the specific complex mentioned in the question.

Explanation

The correct answer refers to the transcription factor complex between Arm and TCF that activates the Siamois gene. The incorrect answers are other components of the Wnt signaling pathway, but they do not form the specific complex mentioned in the question.

22. What can the injection of goosecoid mRNA into ventral vegetal blastomere at the 16-cell stage induce?

Cell death

Cell differentiation

Reduced growth

A new axis.

Injecting goosecoid mRNA into a ventral vegetal blastomere at the 16-cell stage has been shown to induce the formation of a new axis, demonstrating the role of goosecoid in axis determination during embryonic development.

Explanation

Injecting goosecoid mRNA into a ventral vegetal blastomere at the 16-cell stage has been shown to induce the formation of a new axis, demonstrating the role of goosecoid in axis determination during embryonic development.

23. What are the 5 functions of the spemann organiser?

Inhibits gastrulation movements

Promotes cell death in surrounding tissues

Induces formation of the notochord

Initiates gastrulation movements, induces neural tube, self differentiates into dorsal mesoderm, creates an axis, causes surrounding tissue to become paraxial mesoderm (somites) when it would usually become ventral mesoderm.

The spemann organiser plays a critical role in embryonic development by initiating gastrulation movements, inducing neural tube formation, self-differentiating into dorsal mesoderm, creating an axis, and causing surrounding tissue to become paraxial mesoderm. It does not promote cell death, inhibit gastrulation, or induce notochord formation.

Explanation

The spemann organiser plays a critical role in embryonic development by initiating gastrulation movements, inducing neural tube formation, self-differentiating into dorsal mesoderm, creating an axis, and causing surrounding tissue to become paraxial mesoderm. It does not promote cell death, inhibit gastrulation, or induce notochord formation.

24. What does the lateral plate mesoderm form?

Forms nervous system, skeletal system, respiratory system

Forms digestive system, endocrine system, integumentary system

Forms muscular system, lymphatic system, urinary system

Forms circulatory system, body cavity, extra-embryonic

25. What structures are formed by the intermediate mesoderm?

Forms heart, lungs

Forms kidney, gonads

Forms liver, pancreas

Forms brain, spinal cord

26. What is the role of chordamesoderm in embryonic development?

Forms notochord

Develops into the digestive system

Gives rise to neural tube

Differentiates into muscle tissue

Chordamesoderm is a specialized tissue in the developing embryo that gives rise to the notochord, a structure essential for vertebrate development and axial skeleton formation.

Explanation

Chordamesoderm is a specialized tissue in the developing embryo that gives rise to the notochord, a structure essential for vertebrate development and axial skeleton formation.

27. What structures does the paraxial mesoderm form?

B) forms the heart and lungs.

C) forms the liver and pancreas.

A) forms the neural tube and brain.

Forms head and somites, somites go on to form cartilage, skeletal muscle and the dermis.

Paraxial mesoderm is responsible for forming the head and somites, which in turn give rise to cartilage, skeletal muscle, and the dermis.

Explanation

Paraxial mesoderm is responsible for forming the head and somites, which in turn give rise to cartilage, skeletal muscle, and the dermis.