Session 1: Basics and Bottlenecks overview

[Sampurna Chakrabarti]

Speakers: Kristin Baldwin: https://www.scripps.edu/faculty/baldwin/, Lorenz Studer: https://www.mskcc.org/research/ski/labs/lorenz-studer

I am a PhD student at the University of Cambridge researching inflammatory joint pain. Recently I became interested in utilizing induced pluripotent stem cells (iPSC)-derived sensory neurons in my research, hence I was interested in this virtual conference. The first session of this conference provided a perfect platform to familiarize with the field and also helped to know the basics of induced neurons.

Kristin Baldwin from the Scripps research institute started the session with a question that most neuroscientists have thought about at some point in their careers (I certainly did, before moving away from the brain to the periphery): “How to build a brain?” The two main components to answer this question are the cell autonomous mechanisms (that takes place early in development) and external cues (e.g. hormones, late in development). iPSCs are particularly useful for understanding the first component because they can be induced into different neurons. Prof Baldwin discussed the two ways induced neurons can be obtained:

1)      Fibroblast à iPSC à neurons (these are relatively immature neurons)

2)      Fibroblast à neurons via transcriptional factors

In an article published in 2018 (https://www.nature.com/articles/s41586-018-0103-5) her lab described recipes of deriving specific neurons by utilizing transcriptional factors. The paper links to an amazing database where one can find the minimum number of transcriptional factors that they need to make neurons express the receptor of their choice. It’s quite exciting to think that this approach can be extended to understand what can go wrong in disease conditions. Although useful in answering cell autonomous questions, understanding external factors needed to build a brain is tricky; but her lab has come up with a clever technique of inter-species chimeras to dissect these mechanisms. In this model, rat-derived iPSC cells can be injected into mouse to make a part-mouse-part-rat species. In experiments like this the first question is whether an interspecies brain is possible. The Baldwin lab has shown that at least an interspecies functional olfactory system is possible if the mouse neurons are silenced. Therefore, this talk highlighted the different ways neurons can be derived from fibroblasts and provided insights into how iPSCs can help us build a brain!    

Next up was Prof Lorenz Studer from Sloan Kettering and his talk focused on creating iPSC-driven model systems to study diseases in-vitro. The conventional way of connecting genes to clinical phenotype involves identifying de novo mutations in the patient population, mutating mouse genome for that gene followed by functional tests. This process, although rigorous, takes lots of time and resources especially because most diseases involve multiple genetic abnormalities. To overcome this challenge, Studer lab utilizes multiple iPSC cell lines with disease-relevant mutations. These cell lines then can be pooled together in a 2D or 3D (organoid) triple or quadruple co-culture system to mimic disease in a dish. Application of this model system was shown in autism spectrum disorder where human PSCs could re-create the autistic pre-frontal cortex and WNT signaling was shown to be mechanistically affecting neurogenesis.    

 

In conclusion, the major take home points from this session for me were:

1)      Induced neurons carry mutations of their parent fibroblasts, which should be taken into consideration before designing experiments.

2)      There are multiple ways to induce neurons and using the trans-differentiation method we have access to a recipe book that can program neurons to express receptors of our choice.

3)      Multiple iPSC lines (even better if they are patient derived) pooled together can help re-create diseases in more physiological manner in vitro.