WBR0332: Difference between revisions

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{{WBRQuestion
{{WBRQuestion
|QuestionAuthor={{Rim}}
|QuestionAuthor= {{Rim}},  {{AJL}}  {{Alison}}
|ExamType=USMLE Step 1
|ExamType=USMLE Step 1
|Prompt=In an experiment that uses chicks, a researcher removes the apical ectodermal ridge (AER) and finds that only the proximal skeletal segment develops with complete absence of the middle and the distal segments. The researcher then applies beads soaked in recombinant proteins at the tip of the chick limbs that are missing AERs and finds that normal limb development occurs. Protein expressed by which gene is most likely present in the recombinant-soaked beads?
|MainCategory=Genetics
|Explanation=FGF gene is important embryologically for the induction of mitosis of the mesoderm and for the lengthening of the limbs. It is produced by the apical ectodermal ridge (AER). In this experiment, the AER is lost. Consequently, the FGF protein produced by the FGF gene will no longer be present to induce the lengthening of the chick limbs. The chick limbs thus only developed the proximal segment but had misising middle and distal segments. When beads soaked in recombinant FGF protein are introduced to the tip of the limbs that are missing AER, FGF will be present and limb development will occur normally.  
|SubCategory=General Principles
|MainCategory=Genetics
|SubCategory=General Principles
|MainCategory=Genetics
|SubCategory=General Principles
|MainCategory=Genetics
|MainCategory=Genetics
|SubCategory=General Principles
|MainCategory=Genetics
|SubCategory=General Principles
|MainCategory=Genetics
|SubCategory=General Principles
|MainCategory=Genetics
|SubCategory=General Principles
|MainCategory=Genetics
|MainCategory=Genetics
|SubCategory=General Principles
|Prompt=A researcher inactivates the components of the ectoderm rimming of the distal tip of a limb bud, from a mouse, at an early stage. He finds that only the proximal skeletal segment develops with a complete absence of the middle and the distal segments. Then, he applies beads soaked in recombinant proteins at the tip of the limb buds and observes that normal limb development occurs successfully. Protein is most likely expressed by which of the following genes in the recombinant-soaked beads?
|Explanation= Embryologically, the [[fibroblast growth factor]] (FGF) gene induces mitosis of the mesoderm and the lengthening of the limbs. It is produced by the apical ectodermal ridge (AER), which is the ectoderm rimming the distal tip of the limb bud. In this experiment, the AER is lost. Consequently, the FGF protein produced by the FGF gene will no longer be present to induce the lengthening of the limbs. The mice limbs developed the proximal segment but had misising middle and distal segments. When beads soaked in recombinant FGF protein are introduced to the tip of the limbs that are missing AER, limb development occurs normally.  


Educational Objective:
|EducationalObjectives= The FGF gene is located at the apical ectodermal ridge (AER) and is responsible for the lengthening of limbs.
FGF gene is located at the apical ectodermal ridge (AER) and is responsible for the lengthening of limbs.


Reference:
|References= Sun X, Mariani FV, Martin GR. Functions of FGF signaling from the apical ectodermal ridge in limb development. Nature. 2002; 418:501-8
Sun X, Mariani FV, Martin GR. Functions of FGF signaling from the apical ectodermal ridge in limb development. Nature. 2002; 418:501-8  
 
|AnswerA=FGF  
|AnswerA=FGF
|AnswerAExp=FGF is produced at the apical ectodermal ridge (AER). It induces mitosis of the mesoderm and allows for limb lengthening.
|AnswerAExp=The fibroblast growth factor (FGF), produced at the apical ectodermal ridge (AER), induces mitosis of the mesoderm and allows for limb lengthening.
|AnswerB=Sonic hedgehog
|AnswerB=Sonic hedgehog
|AnswerBExp=Sonic hedgehog gene is produced at the base of the limbs. It is involved in CNC development.
|AnswerBExp=The sonic hedgehog gene, produced at the base of the limbs, is involved in CNS development.
|AnswerC=Wnt-7
|AnswerC=Wnt-7
|AnswerCExp=Wnt-7 gene is produced at apical ectodermal ridge (AER). It is involved in the organization along dorso-ventral axis.
|AnswerCExp=The wnt-7 gene, produced at apical ectodermal ridge (AER), is involved in the organization along dorso-ventral axis.
|AnswerD=Homeobos (Hox)
|AnswerD=Homeobox
|AnswerDExp=Hox gene is involved in segmental organization along the cranio-caudal direction.
|AnswerDExp=The homeobox (Hox) gene is involved in segmental organization along the cranio-caudal direction.
|AnswerE=SRY
|AnswerE=SRY
|AnswerEExp=SRY gene is located on the Y chromosome. It is involved in the production of testis-determining factor.
|AnswerEExp=The SRY gene, located on the Y chromosome, is involved in the production of the testis-determining factor.
|RightAnswer=A
|RightAnswer=A
|WBRKeyword=embryogenesis, FGF, gene, protein, apical, ectodermal, ridge, AER, limb, length, lengthening, mesoderm, mitosis, bead, soak, soaked, recombinant
|WBRKeyword=embryogenesis, FGF, genes, proteins, apical, ectodermal, ridge, AER, lengthening, mesoderm, mitosis,
|Approved=No
}}
}}

Latest revision as of 00:12, 28 October 2020
Author [[PageAuthor::Rim Halaby, M.D. [1], Alison Leibowitz [2] (Reviewed by Alison Leibowitz)]]
Exam Type ExamType::USMLE Step 1
Main Category MainCategory::Genetics
Sub Category SubCategory::General Principles
Prompt [[Prompt::A researcher inactivates the components of the ectoderm rimming of the distal tip of a limb bud, from a mouse, at an early stage. He finds that only the proximal skeletal segment develops with a complete absence of the middle and the distal segments. Then, he applies beads soaked in recombinant proteins at the tip of the limb buds and observes that normal limb development occurs successfully. Protein is most likely expressed by which of the following genes in the recombinant-soaked beads?]]
Answer A AnswerA::FGF
Answer A Explanation AnswerAExp::The fibroblast growth factor (FGF), produced at the apical ectodermal ridge (AER), induces mitosis of the mesoderm and allows for limb lengthening.
Answer B AnswerB::Sonic hedgehog
Answer B Explanation AnswerBExp::The sonic hedgehog gene, produced at the base of the limbs, is involved in CNS development.
Answer C AnswerC::Wnt-7
Answer C Explanation AnswerCExp::The wnt-7 gene, produced at apical ectodermal ridge (AER), is involved in the organization along dorso-ventral axis.
Answer D AnswerD::Homeobox
Answer D Explanation AnswerDExp::The homeobox (Hox) gene is involved in segmental organization along the cranio-caudal direction.
Answer E AnswerE::SRY
Answer E Explanation AnswerEExp::The SRY gene, located on the Y chromosome, is involved in the production of the testis-determining factor.
Right Answer RightAnswer::A
Explanation [[Explanation::Embryologically, the fibroblast growth factor (FGF) gene induces mitosis of the mesoderm and the lengthening of the limbs. It is produced by the apical ectodermal ridge (AER), which is the ectoderm rimming the distal tip of the limb bud. In this experiment, the AER is lost. Consequently, the FGF protein produced by the FGF gene will no longer be present to induce the lengthening of the limbs. The mice limbs developed the proximal segment but had misising middle and distal segments. When beads soaked in recombinant FGF protein are introduced to the tip of the limbs that are missing AER, limb development occurs normally.

Educational Objective: The FGF gene is located at the apical ectodermal ridge (AER) and is responsible for the lengthening of limbs.
References: Sun X, Mariani FV, Martin GR. Functions of FGF signaling from the apical ectodermal ridge in limb development. Nature. 2002; 418:501-8]]

Approved Approved::
Keyword WBRKeyword::embryogenesis, WBRKeyword::FGF, WBRKeyword::genes, WBRKeyword::proteins, WBRKeyword::apical, WBRKeyword::ectodermal, WBRKeyword::ridge, WBRKeyword::AER, WBRKeyword::lengthening, WBRKeyword::mesoderm, WBRKeyword::mitosis
Linked Question Linked::
Order in Linked Questions LinkedOrder::
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