Passage
Osteoarthritis (OA) is a disorder marked by the deterioration of articular (hyaline) cartilage, the connective tissue lining the ends of bones at most movable joints. The progressive erosion of articular cartilage in OA is thought to be caused by an inflammatory response induced by years of biomechanical stress due to excessive compression and friction. This response involves the release of proteolytic enzymes that break down cartilaginous proteins. The progressive breakdown of articular cartilage ultimately results in complete exposure of the cortical portion of the underlying subchondral bone with narrowing of the joint space. Repeated and abnormal joint stress can also cause the development of osteophytes, or bony growths, that form on the subchondral bone. These degenerative processes cause pain and restrict joint movement.Stem cell therapy, in which injected or grafted stem cells are induced to differentiate into chondrocytes (cartilage cells) , is a potential new treatment for OA. To further understand chondrogenesis, researchers have been studying the molecules that regulate the expression and activity of the transcription factor Sox9, which has been shown to promote chondrocyte differentiation. For example, researchers have found that binding of the growth factor TGF-β to its receptor results in Sox9 activation.MicroRNAs (miRNAs) , which are known to alter gene expression by acting at the translational level, are also potential regulators of Sox9. In particular, miRNA-145 is thought to regulate Sox9 expression by binding to the 3′-UTR of the Sox9 mRNA transcript. After chondrocyte differentiation was induced using TGF-β, researchers used Western blotting to generate an expression profile of Sox9 and β-actin (a protein not regulated by miRNA-145) in mouse stem cells transfected with miRNA-145, anti-miRNA-145, or neither (Figure 1) .
Figure 1 Expression of Sox9 in the presence and absence of miRNA-145 or anti-miRNA-145 following induction of chondrocyte differentiation
Adapted from Yang B, Guo H, Zhang Y, Chen L, Ying D, Dong S. MicroRNA-145 regulates chondrogenic differentiation of mesenchymal stem cells by targeting Sox9. PLoS ONE. 2011;6(7) :e21679.
-Luciferase is an enzyme responsible for bioluminescence (light emission) . Researchers engineered a reporter vector (shown below) that results in the expression of a hybrid transcript containing luciferase and the Sox9 3′- UTR. The vector was transfected into two groups of mouse stem cells, Group A and Group B. Cells in Group B were also transfected with a miR-145 mimic, which was designed to imitate mature endogenous miRNA in the cell. Given this information, luciferase bioluminescence will most likely be detected in:

Question

Passage
Osteoarthritis (OA) is a disorder marked by the deterioration of articular (hyaline) cartilage, the connective tissue lining the ends of bones at most movable joints. The progressive erosion of articular cartilage in OA is thought to be caused by an inflammatory response induced by years of biomechanical stress due to excessive compression and friction. This response involves the release of proteolytic enzymes that break down cartilaginous proteins. The progressive breakdown of articular cartilage ultimately results in complete exposure of the cortical portion of the underlying subchondral bone with narrowing of the joint space. Repeated and abnormal joint stress can also cause the development of osteophytes, or bony growths, that form on the subchondral bone. These degenerative processes cause pain and restrict joint movement.Stem cell therapy, in which injected or grafted stem cells are induced to differentiate into chondrocytes (cartilage cells) , is a potential new treatment for OA. To further understand chondrogenesis, researchers have been studying the molecules that regulate the expression and activity of the transcription factor Sox9, which has been shown to promote chondrocyte differentiation. For example, researchers have found that binding of the growth factor TGF-β to its receptor results in Sox9 activation.MicroRNAs (miRNAs) , which are known to alter gene expression by acting at the translational level, are also potential regulators of Sox9. In particular, miRNA-145 is thought to regulate Sox9 expression by binding to the 3′-UTR of the Sox9 mRNA transcript. After chondrocyte differentiation was induced using TGF-β, researchers used Western blotting to generate an expression profile of Sox9 and β-actin (a protein not regulated by miRNA-145) in mouse stem cells transfected with miRNA-145, anti-miRNA-145, or neither (Figure 1) .

Figure 1 Expression of Sox9 in the presence and absence of miRNA-145 or anti-miRNA-145 following induction of chondrocyte differentiation
Adapted from Yang B, Guo H, Zhang Y, Chen L, Ying D, Dong S. MicroRNA-145 regulates chondrogenic differentiation of mesenchymal stem cells by targeting Sox9. PLoS ONE. 2011;6(7) :e21679.
-Luciferase is an enzyme responsible for bioluminescence (light emission) . Researchers engineered a reporter vector (shown below) that results in the expression of a hybrid transcript containing luciferase and the Sox9 3′- UTR.

The vector was transfected into two groups of mouse stem cells, Group A and Group B. Cells in Group B were also transfected with a miR-145 mimic, which was designed to imitate mature endogenous miRNA in the cell. Given this information, luciferase bioluminescence will most likely be detected in:

Quizplus · Accepted Answer

11ecba2d_0fc7_0b08_a3bf_59352711b2f4_MD0008_00 Reporter genes express easily identified (ie, fluorescent, luminescent) protein products and are consequently used to determine the effects of certain regulatory sequences or measure the expression of other genes. For example, reporter genes can be used to determine whether transfection, the incorporation of foreign genetic material into animal cells, has been successful. This is done by including the reporter gene sequence in the vector (the DNA molecule engineered to carry the foreign DNA into the host cell). In addition, in gene expression assays, the reporter gene sequence is fused to the gene or gene region of interest and results in a hybrid transcript, allowing researchers to identify gene expression changes under varying experimental conditions. The passage states that miRNA-145 regulates Sox9 gene expression by binding the 3′-UTR region of the Sox9 mRNA transcript. Binding of miRNA to the 3'-UTR region of an mRNA transcript will generally prevent translation of the entire transcript. The Western blot data in the passage shows that Sox9 expression is absent in the presence of miRNA-145, signifying that miRNA-145 inhibits Sox9 expression and consequently prevents chondrogenic differentiation in the cell. Per the question, the luciferase enzyme is responsible for bioluminescence (emission of light by a living organism). The construct (vector) was engineered to result in a hybrid transcript containing luciferase and the Sox9 3′-UTR. However, treatment with the miRNA-145 mimic would prevent luciferase expression by binding the Sox9 3′-UTR region and blocking translation of the entire transcript. Therefore, bioluminescence would be observed in the control group (Group A), which was not treated with the miRNA-145 mimic (Choice D). However, bioluminescence would not be observed in the experimental group (Group B), which expresses miRNA-145 (Choices B and C). Educational objective: A reporter gene allows researchers to study the regulation or expression of other genes. The luciferase gene is a commonly used reporter gene whose protein product catalyzes a reaction that results in bioluminescence, which allows easy expression quantification of the target gene.