Weekly reads: chimera cat vs. chimeric rat, cheap sequencing, more

When you are a stem cell biologist and especially if you do a blog, you sometimes run across very strange things like a chimera cat. In this case, I stumbled on the whole topic of chimeric cats because I was searching for info on chimeric rats on Google.

Of course, I was.

cat chimera
Venus the cat chimera. Picture from the Today Show.

It’s kind of a side note, but it turns out that cat chimeras are not that uncommon. Apparently, cat embryos can fuse together fairly often and still yield one living, healthy cat. That’s generally what is meant when people talk about “chimera cats” on the internet, it seems. You can see a picture above of Venus the chimeric cat.

It can sort of happen in people too but is extremely rare. Sometimes when human embryos fuse, this event leads to the production of conjoined twins.

Also, we humans more generally are likely all technically chimeric to a small extent in a different sense. Our cells can have subtle but potentially important genomic differences from each other. Below is a video version of the discussion of chimeras.

Chimeric rats with human brain cells

How do this whole topic come up?

There’s a new paper that made headlines about transplantation of human brain organoids into rats. The resulting rodents are chimeras. I’ll start our weekly reads with that paper.

Here’s an overview article by Carl Zimmer in the NYT:Human Brain Cells Grow in Rats, and Feel What the Rats Feel.

This is an intriguing piece. However, I don’t agree with the use of the word “feel” in the headline. To feel something is more of a whole organism experience. I’d say the NYT should have used the word “sense”.

What do you think? Can neurons “feel” something?

Here’s the original Nature paper: Maturation and circuit integration of transplanted human cortical organoids.

Something similar has been done by other labs. For instance, Rusty Gage’s lab published An in vivo model of functional and vascularized human brain organoids in mice in 2018 in Nature Biotechnology. A UC Davis team also reported implantation of human organoids into mouse brain around the same time.

Other kinds of human-animal chimeras have been made including pig chimeras.

These types of chimeric experiments are fascinating, but they raise complicated ethical issues too as I’ve discussed in the past. What percent of an animal brain’s cells being human would be too much? How could we even decide such a thing?

There could be another type of chimera in a sense related to the brain if someone ever successfully does head transplants. See my video above on this idea. It’s not happening any time soon.

More recommended reads

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