TeachableMedicalNews article TMN12112022

Teachable moment in classrooms:

  1. cellular basis of life chapter – concept of one gene, one protein
  2. cellular basis of life chapter – protein synthesis on ribosomes
  3. skeletal system chapter – actions of osteoblasts and osteoclasts in living bones
  4. skeletal system chapter – osteons and trabeculae provide structural strength to bones
  5. endocrine system chapter – actions of PTH made by parathyroid gland

The news item:  Recently the following report appeared in cyberspace:

Humans on Mars may feast on gene-edited salad to stop bones breaking

Genetically modified salad could be crucial to keeping the bones of humans on Mars healthy.

The article states that a human gene was added to lettuce, and that the human protein, parathyroid hormone (PTH), will fight the osteoporosis that astronauts develop in space. Astronauts lose 1.5% of bone mass from weight-bearing bones, and the expectation is the PTH made by the lettuce will prevent bone loss on a trip to Mars that may last for over a year.

So, Why Do I Care??  Osteoporosis, as stated in the article, weakens bones, but not only in astronauts. Over 10 million people in the US alone has osteoporosis that makes fractures more likely. PTH is currently administered through injections, so, if we could demonstrate that eating PTH-enriched lettuce, then treatment of osteoporosis may become easier.

Plain English, Please!!! First, let’s summarize what osteoporosis is, and how astronauts taking PTH can fight it (this was explored in detail in TMN article 11272022). The microscopic structural reinforcement structures (osteons and trabeculae) in our bones erode, gets degraded in the disorder called osteoporosis.  Imagine a tall building or a bridge; columns or pillars are the elements of structural reinforcement in them. A corrosion of those pillars and columns weakens the building, and may cause their collapse. Astronauts in space don’t have the force of gravity to stimulate bone building, so bone loss, osteoporosis develops. PTH, when administered in short bursts, stimulates osteoblasts, and increases bone formation, and that could prevent bone loss in astronauts. Although astronauts could inject themselves with PTH, however, for long spaceflights they would have to carry lots of PTH doses. It would be better if they could produce PTH during the flight itself.  Making human PTH inside a food item would create a continuous supply of PTH.

Second, let’s talk about what is entailed with the genetic engineering of the lettuce. In general, we do genetic engineering when we are adding a new gene or inactivating an existing gene in an organism. Imagine 18 books on a bookshelf; these are the 18 chromosomes (DNA ribbons) in each lettuce cell. We see over 1000 sentences in each book; these are the genes of the lettuce. If we write a new sentence into any of those books, then we genetically engineered the lettuce. In this case the human PTH gene (sentence) is inserted in the middle of tens of thousands of lettuce genes.

Third, let’s talk about how could a plant make human proteins. At first it might seem weird that a human piece of DNA inserted into the large stretch of lettuce DNA will be leading to the production of a human protein inside a lettuce cell. Lettuce cells can make human proteins, because plant cells use the same basic ways to make proteins as human cells.  Messenger RNA is made from the inserted PTH gene, then the messenger RNA is translated into protein using amino acids. Because the identity and function of a protein is determined by the DNA sequence (the gene) encoding it, human PTH can be made by lettuce cells.

 

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