Session 124

We tackle passage 5 from Next Step full-length 10 which talks about peripheral nerves and stem cells. Follow along with the handouts at themcatpodcast.com.

As always, we’re joined by Clara from Blueprint MCAT (formerly Next Step Test Prep) as we take a deep dive into another Bio/Biochem passage. Please take a listen to all our other podcasts on MedEd Media Network.

[03:53] Passage 5

Injuries to peripheral nerves are common and after injury, the proximal stump of the nerve is capable of regeneration and reinnervation. Repair requires bridging the gap and the introduction of Schwann cells, growth factors, and an extracellular matrix for guiding axonal extension and nerve regeneration. Axons regenerated along align Schwann cells, called Bands of Büngner.

Stem cells may prove useful to treat spinal cord injuries. The availability of large numbers of human epidermal neural crest stem cells, hEPI-NCSC for autologous use and for disease modeling and drug discovering is highly desirable. hEPI-NCSC cells are biologically the most relevant cell plate to generate Schwann cells as they are direct descendants of the embryonic neural crest.

Notably, hEPI-NCSC can be isolated via a small biopsy of hairy skin. And they could be expanded ex vivo into millions of stem cells at adherent culture. In addition, hEPI-NCSC-derived Schwann cells express neurotrophins and other growth factors essential for nerve regeneration.

Angiogenesis is crucial for nerve repair. In vivo, Schwann cell precursors differentiate into immature Schwann cells which undergo terminal differentiation into one of two types of mature Schwann cell – myelinating and nonmyelinating. These mature cells rapidly proliferate with a doubling time of 12 hours. Schwann cell differentiation and maintenance are dependent on growth factors that are provided by the embryonic microenvironment and the axons with which they interact. To identify and examine the genes necessary for proper Schwann cell production, a comprehensive gene knock out profile was generated with RNA from hEPI-NCSC-derived Schwann cells. Individual genes were knocked out and then Schwann cell proliferation was measured by cell count after 24 hours.

[06:10] Question 22

Which of the following is not a potential advantage of using hEPI-NCSC over adult stem cells in the study?

• (A) hEPI-NCSC and Schwann cells are both derived from the same precursor.
• (B) The significant migratory ability of neuro crest cells means that there’s no need for purification of cell cultures.
• (C) hEPI-NCSCs do not form tumors in vivo, which is the homework of adult stem cells.
• (D) In vivo, hEPI-NCSC cells translocate away from the neural tube and give rise to a wide array of cell types and tissues.

Clara’s insights:

The right answer here is D. Just because it’s not mentioned in the passage doesn’t necessarily mean it’s wrong. In this case, the migratory activity in Choice B wasn’t mentioned either. And the “tumors” from Choice C weren’t really mentioned. Here, we’re just trying to figure out what is rational and what isn’t, hence, we came up with D.

If the cells don’t form tumors, that seems like an advantage since tumors would seem like a disadvantage. And then for B, the reason that migratory ability is an advantage is that neural crest cells are the cells we’re trying to isolate very close to their precursors. So if they had a significant migratory ability to travel far away, then we might not need to purify these cell cultures. You may only be left with the type of cell you want which migrated far away from the very similar precursors that might have been located into original position.

[11:55] Question 23:

Current hEPI-NCSC treatments require that they can be used as a source of the stem cells utilized in their treatment. This is because:

• (A) Using the host cells eliminates the need for ethical considerations.
• (B) It controls for the effect of external confounding variables in the treatment.
• (C) It reduces the chance of stem cell rejection by the host.
• (D) It reduces the incidence of crest cell-derived tumors.

Clara’s insights:

The correct answer here is C. There’s nothing special about stem cells. Any type of cell coming from another foreign cell to us is going to potentially raise the risk of rejection.

[13:55] Question 25

Damage to which of the following cell structures would not cause the mitotic rates measured in the experiment to be reduced.

• (A) Nucleolus
• (B) Kinetochore
• (C) Centrosome
• (D) Aster

Clara’s insights:

The correct answer here is A because B, C, and D are all involved in mitosis and A is not involved. The nucleolus is where we produce our ribosomal RNA, which is not directly involved in mitosis while the other ones are. The kinetochore is a protein complex found on the centromere. The centromere is where the chromosomes are being joined together and they’re being pulled apart by spindle fibers and the Kinetochore is the part of proteins on the centromere that the spindle fiber is attached to.

[16:20] Question 26

Which is the following cell types performs functions in the central nervous system and now, gets the Schwann cells?

• (A) Chondrocytes
• (B) Microglia
• (C) Oligodendrocytes
• (D) Ependymal cells

Clara’s insights:

The correct answer here is C. Schwann cells have something to do with wrapping the peripheral nerves. The question is what wraps the nerve in the central nervous system. They are two very cell types but different locations.

[17:20] Need help?

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Links:

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