Passage
Neurulation refers to the early formation of the nervous system in vertebrate embryos and begins when the notochord, a rodlike mesodermal structure, induces neural tube and neural crest cell formation in the ectoderm. Neural tube defects (NTDs) arise from abnormalities in the development of the neural tube and can range from mild to severe, depending on which portion of the tube is affected. Spina bifida, a form of NTD, is divided into three categories. The most serious subclassification of spina bifida is myelomeningocele, which occurs when the lower spine fails to close, which leaves the spinal cord and nerve roots in the lower back damaged and exposed.NTDs are thought to be caused in part by folate deficiency. Folate plays a critical role in normal cell division and growth as it is a necessary coenzyme for DNA synthesis and methylation. Mutations in several genes involved in folate metabolism have been associated with an increased risk for NTDs. It has been hypothesized that folate decreases NTD risk by ameliorating oxidative stress, thereby reducing damage to developing cells in the embryo. Certain maternal conditions, such as high blood glucose, increase the risk of NTD development by enhancing embryonic oxidative stress during crucial developmental periods.A study was conducted to examine how supplementation with folic acid, the dietary form of folate, affected pregnant women who were identified to have preexisting diabetes, pregestational obesity (another risk factor for NTD), or no preexisting conditions (control group). Higher folic acid intake decreased the incidence of embryonic NTDs among pregnant women with diabetes, but no significant effect was found for pregnant women who were obese.
Adapted from Parker SE, Yazdy MM, Tinker SC, Mitchell AA, Werler MM. The impact of folic acid intake on the association among diabetes mellitus, obesity, and spina bifida. Am J Obstet Gynecol. 2013;209(3):239.e1-8.
-In vertebrates, researchers found that the concentration pattern of the signaling proteins Sonic Hedgehog (Shh) and Bone Morphogenic Protein (BMP) defined specific regions of expression for various genes involved in neural tube development. The results of their investigation are shown in the graph provided. Based on the data, which statement best explains how Shh specifies the dorsal and ventral fates of the developing neural tube?

Question

Passage
Neurulation refers to the early formation of the nervous system in vertebrate embryos and begins when the notochord, a rodlike mesodermal structure, induces neural tube and neural crest cell formation in the ectoderm.  Neural tube defects (NTDs) arise from abnormalities in the development of the neural tube and can range from mild to severe, depending on which portion of the tube is affected.  Spina bifida, a form of NTD, is divided into three categories.  The most serious subclassification of spina bifida is myelomeningocele, which occurs when the lower spine fails to close, which leaves the spinal cord and nerve roots in the lower back damaged and exposed.NTDs are thought to be caused in part by folate deficiency.  Folate plays a critical role in normal cell division and growth as it is a necessary coenzyme for DNA synthesis and methylation.  Mutations in several genes involved in folate metabolism have been associated with an increased risk for NTDs.  It has been hypothesized that folate decreases NTD risk by ameliorating oxidative stress, thereby reducing damage to developing cells in the embryo.  Certain maternal conditions, such as high blood glucose, increase the risk of NTD development by enhancing embryonic oxidative stress during crucial developmental periods.A study was conducted to examine how supplementation with folic acid, the dietary form of folate, affected pregnant women who were identified to have preexisting diabetes, pregestational obesity (another risk factor for NTD), or no preexisting conditions (control group).  Higher folic acid intake decreased the incidence of embryonic NTDs among pregnant women with diabetes, but no significant effect was found for pregnant women who were obese.
Adapted from Parker SE, Yazdy MM, Tinker SC, Mitchell AA, Werler MM. The impact of folic acid intake on the association among diabetes mellitus, obesity, and spina bifida. Am J Obstet Gynecol. 2013;209(3):239.e1-8.
-In vertebrates, researchers found that the concentration pattern of the signaling proteins Sonic Hedgehog (Shh) and Bone Morphogenic Protein (BMP) defined specific regions of expression for various genes involved in neural tube development.  The results of their investigation are shown in the graph provided.  Based on the data, which statement best explains how Shh specifies the dorsal and ventral fates of the developing neural tube?

Quizplus · Accepted Answer

11ecba2d_0fc2_9e30_a3bf_05be04d99063_MD0008_00 A morphogen is a signaling molecule that alters embryonic cell differentiation in a concentration-dependent manner, and competent cells are cells that express receptors capable of responding to that morphogen. Once released into the extracellular space by signaling cells, morphogens diffuse from one region of the embryo to another, creating a concentration gradient. Competent cells closer to the signaling cell are exposed to higher morphogen concentration and will consequently undergo fate determination and differentiation distinct from the competent cells that are farther away (ie, those that are exposed to lower morphogen concentration). Therefore, morphogens are a type of paracrine factor that helps control organ development and body axis formation (eg, anterior-posterior, dorsal-ventral). The figure shows that the concentrations of sonic hedgehog (Shh) and bone morphogenic protein (BMP) vary along the embryonic dorsal-ventral axis, suggesting that both molecules are opposing morphogens that determine cell fate based on their relative concentration gradients. In other words, certain combinations of morphogen levels signal for the expression of different genes. For example, high BMP/low Shh concentrations result in Pax7 expression to define the dorsal end of the neural tube, and low BMP/high Shh concentrations result in Pax6 expression to define the ventral end. At intermediary (mixed) BMP/Shh concentrations, other genes (Dbx1, Dbx2, Irx3) are activated to induce proper differentiation along the body axis. Thus, depending on concentration, Shh and BMP can signal for both ventral and dorsal differentiation and development (Choice C). (Choice A) No data is provided to indicate whether or not Shh promotes the expression of genes involved in cell division. (Choice D) The question states that both BMP and Shh are signaling proteins, not receptors. Educational objective: Morphogens are signaling molecules that influence cell differentiation in the embryo. They are released by signaling cells and diffuse outward to alter gene expression in competent cells in a concentration-dependent manner.

Passage Neurulation Refers to the Early Formation of the Nervous System