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Two key factors affect the genetic expression that ultimately determines an embryonic cell’s fate, cytoplasmic segregation and external induction of neighboring stem cells. External induction is prevalent in vertebrate embryonic development.

During the 1980s, a genus of closely studied amphibians, Xenopus, the clawed frogs, provided evidence of a major induction event to a group of biologists. They were able to witness the interaction between mesodermal and ectodermal layers in neural cell formation, soon followed by the activation of sodium pumps.

Induction involves the release of inducer molecules from designated inducting anchor tissue to nearby responding tissue that then experiences a shift in cell differentiation. Inducer reception on the responding, or precursor cells, triggers a series of steps that direct a stem cell’s new fate.

During the Xenopus tissue induction experiments, biologists performed molecular assays in order to extract and identify molecular evidence of neural-specific gene transcripts. This was used to verify differentiation by induction was successful.

Which of the following steps in cell induction would directly yield gene transcripts relevant to nerve cell properties?

A

The release of inducer molecules from inducer cells will directly activate the responding nerve cell’s genes.

B

The reception of the inducer molecule will complete the successive events required for transcription of relevant genes, creating proteins required for nerve cell function.

C

The formation of the three embryonic germ layers, ectoderm, mesoderm and endoderm, must begin immediately after induction in order for a nerve cell to engage its necessary genes.

D

Following induction, initiation of signal transduction cascade events inside a precursor cell results in the transcription of genes important for differentiated nerve cells.

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