The following statements are made regarding the amphibian early-embryonic development: A. The Nieuwkoop center cells are mesodermal in origin. B. Chordin, Noggin and Goosecoid are secreted by the Organizer. C. The default fate of the ectoderm is to become neural tissue. D. BMP levels are high in the presumptive dorsal mesoderm. Which one of the following options represents the combination of all correct statements?
B and C only
Amphibian Embryonic Development Statements Analysis
The question asks us to identify the correct statements regarding early embryonic development in amphibians. Let's analyze each statement:
A. The Nieuwkoop center cells are mesodermal in origin.
The Nieuwkoop center is a signaling region located in the dorsal-vegetal part of the amphibian embryo. It arises from the vegetal endoderm cells influenced by maternal factors. It is crucial for inducing the dorsal mesoderm (including the Organizer). However, the cells themselves are vegetal endoderm, not mesoderm. Therefore, this statement is incorrect.
B. Chordin, Noggin and Goosecoid are secreted by the Organizer.
The Organizer, also known as the Spemann-Mangold Organizer, is a region in the dorsal mesoderm induced by the Nieuwkoop center. The Organizer secretes several signaling molecules, including Chordin, Noggin, and Goosecoid. These molecules function, in part, by inhibiting Bone Morphogenetic Protein (BMP) signaling in the overlying ectoderm and adjacent mesoderm, thereby promoting neural and dorsal mesoderm development. This statement is correct.
C. The default fate of the ectoderm is to become neural tissue.
In amphibian embryos, the ectoderm can develop into epidermis or neural tissue. Studies, including dissociation-reaggregation experiments, have shown that if ectodermal cells are cultured in isolation without specific signals, they tend to differentiate into neural tissue. This suggests that the underlying default pathway for ectoderm is neural, and external signals (like BMPs) are required to promote the epidermal fate. The Organizer's role is to secrete BMP inhibitors, thus allowing the default neural fate to be expressed in the dorsal ectoderm. This statement is correct.
D. BMP levels are high in the presumptive dorsal mesoderm.
Bone Morphogenetic Proteins (BMPs), particularly BMP4, are important signaling molecules in early development. High levels of BMP signaling promote ventral fates (epidermis in ectoderm, ventral mesoderm). In amphibian embryos, BMP signaling is typically high in the ventral side and low in the dorsal side. The Organizer region (which forms part of the dorsal mesoderm) actively secretes inhibitors of BMP signaling (like Chordin, Noggin), resulting in low BMP levels in the presumptive dorsal mesoderm and overlying dorsal ectoderm. Therefore, this statement is incorrect.
Based on the analysis:
- Statement A is incorrect.
- Statement B is correct.
- Statement C is correct.
- Statement D is incorrect.
The combination of all correct statements is B and C.
| Statement | Evaluation | Correctness |
|---|---|---|
| A. Nieuwkoop center mesodermal origin | Nieuwkoop center is vegetal endoderm. | Incorrect |
| B. Chordin, Noggin, Goosecoid secreted by Organizer | Organizer secretes these factors to inhibit BMPs. | Correct |
| C. Default fate of ectoderm is neural tissue | Ectoderm differentiates into neural tissue without BMP signals. | Correct |
| D. High BMP levels in presumptive dorsal mesoderm | BMP levels are low in the dorsal side due to inhibitors. | Incorrect |
Thus, statements B and C are correct.
Important Questions from Morphogenesis and organogenesis in animals
The individuals considered in this question are having two haploid sets of autosomes and no Y- chromosome. The X∶A ratio of the individuals, the type of organisms chosen, their primary sex and number of Barr bodies expected in their cells are shown in the table below:
X∶A ratio Organism Primary Sex Number of Barr bodies i. 0.5
ii. 2
A. Human
B. Drosophila
I. Male
II. Female
III. Metafemale
a. Zero
b. One
c. Two
d. Three
Select the option below with all correct matches:
Several marine organism release their gametes into the environment, where sperm attraction and subsequent events lead to successful fertilization. With reference to sea urchins, which one of the following statements is NOT true?
The following statements regarding the generation of dorsal/ventral axis in Drosophila was made:
A. Gurken protein moves along with the oocyte nucleus and signals follicle cells to adopt the ventral fate.
B. Maternal deficiencies of either the gurken or torpedo gene cause ventralization of the embryo.
C. Gurken is active only in the oocyte and Torpedo is active only in the somatic follicle cells.
D. The Pipe protein is made in the dorsal follicle cells.
E. The highest concentration of Dorsal is in the dorsal cell nuclei, which becomes the mesoderm.
Which one of the following combination of the above statements is true?
During wing development in chick, if Apical Ectodermal Ridge (AER) is removed, the limb development ceases, on the other hand placing leg mesenchyme directly beneath the wing AER, distal hindlimb structures develop at the end of the wing, and if limb mesenchyme is replaced by non-limb mesenchyme beneath AER, the AER regresses. This may demonstrate that:
A. the limb mesenchyme cells induce and sustain AER.
B. the mesenchyme cells specify the type: wing or limb.
C. the AER is responsible for specifying the type: wing or limb.
D. the AER is responsible for sustained outgrowth and development of the limb.
E. the AER does not specify the type: wing or limb.
Which combination of above statements is demonstrated by the experiment?
The hedgehog pathway is extremely important in vertebrate limb development, neural differentiation and facial morpho-genesis. In accordance with the above statement, what would happen in mice that are homozygous for a mutant allele of sonic hedgehog (shh)?
