In Xenopus, the Noggin protein, accomplishes two major functions of the organizer: it induces dorsal ectoderm to form neural tissues, and it dorsalizes mesoderm cells. Which one of the following observations is correct with respect to Noggin?
If a plasmid clone expressing Noggin protein is microinjected into UV-treated embryo which does not give rise to neural tube, it will rescue the abnormality.
Noggin Protein in Xenopus Development
Noggin is a secreted protein that plays crucial roles in the early development of the Xenopus embryo. It is known to act as a signaling molecule emanating from the organizer region, specifically the dorsal blastopore lip.
Functions of Noggin
The question highlights two major functions of Noggin:
- Induces dorsal ectoderm to form neural tissues (neural induction).
- Dorsalizes mesoderm cells.
These functions are critical for establishing the dorsal side of the embryo and forming the central nervous system.
UV-treated Xenopus Embryo
UV irradiation of a Xenopus embryo is a common method used to study developmental signaling. UV treatment damages the vegetal cytoplasm, particularly the cortical rotation mechanism, which is essential for setting up the dorsal-ventral axis. A UV-treated embryo typically fails to form a dorsal side, resulting in a ventralized embryo that lacks structures like the notochord and the neural tube.
Analyzing Noggin Effects on UV-treated Embryo
Given that a UV-treated embryo is ventralized and lacks a neural tube (a structure derived from induced dorsal ectoderm), introducing a dorsalizing and neural-inducing factor like Noggin should counteract these defects.
If a plasmid clone expressing Noggin protein is microinjected into a UV-treated embryo, the Noggin protein produced would signal to the surrounding cells. Based on its known functions:
- Noggin would induce the dorsal ectoderm (or the ectoderm that would normally become dorsal) to form neural tissue, potentially rescuing the formation of the neural tube.
- Noggin would dorsalize the mesoderm, helping to restore dorsal mesodermal structures like the notochord.
Therefore, microinjecting Noggin into a UV-treated embryo is expected to "rescue" the abnormality by promoting dorsal development and neural tube formation.
Evaluating Other Options
- Option 1: Lithium chloride treatment causes hyperdorsalization, the opposite of the UV-induced ventralization. Injecting a dorsalizing factor like Noggin into a hyperdorsalized embryo would likely worsen the condition, not rescue it.
- Option 3: Noggin is secreted by the organizer, which is located at the dorsal blastopore lip. Therefore, RNA in situ hybridization would show noggin mRNA expression primarily in the dorsal blastopore lip, not in all regions except the dorsal blastopore lip. This statement is incorrect.
- Option 4: Injecting noggin mRNA into the ventral region would cause the ventral cells to produce Noggin protein. Since Noggin promotes dorsalization and neural induction, its presence in the ventral region would cause those cells to adopt more dorsal or neural fates, promoting dorsalization, not ventralization.
Based on the functions of Noggin and the effects of UV treatment, microinjecting Noggin into a UV-treated embryo is expected to rescue the neural tube formation and dorsal development.
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 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?
