Yesterday at ISSCR 2016, Fiona Watt gave a great talk about plasticity of epidermal stem cells. As with my other #ISSCR2016 posts, this one is a stream of impressions, quotes, and key points. For my other blog posts from the meeting see here.
First she provided a nice overview of human skin architecture and regulation. The position of cells within this tissue directly impacts their fate and this is true of the stem cells as well. How do stem cells in the basal layer adopt specific fates as they commit and then differentiate?
Her team looked for surface markers that link to clonogenic potential of stem cells. The ability to form clonal colonies is an assay for the actual stem cells in the epidermis. They found specific markers that are elevated in human epidermal stem cells.
Different microenvironmental cues trigger differentiation via different signal transduction pathways, which includes cues such as micropatterned island versus soft, porous gel.
What regulates commitment?
They looked at gene expression in suspension (t-SNE statistical analysis of different time points). There was a poor correlation between mRNA and protein at 4h in suspension (adding my two cents–so studies like Affymetrix and RNA-Seq clearly do not always tell the whole story). Are there post-transcriptional/post-translational changes taking place?
A major finding is that protein dephosphorylation is a characteristic of commitment. Spike in phosphatase activity at the same time.
Phosphatase KD gave mixed results of more or fewer colonies depending on the phosphatase targeted. Thus, the balance of difference phosphatase activities will be central. Changes were apparent in differentiation and proliferation in a neat in vitro epidermis model (building epidermis on de-epidermalized skin). There are pro-commitment phosphatases that impact AP1 factors.
Some focus on DUSP10 (opposite effect of pro-commitment factors and they may antagonize). Why is commitment state transient?
Exit the niche, downregulation of MAPK, increase in pro-commitment phosphatases. DUSP10 makes commitment transient.
- Do different external stimuli trigger a common commitment state?
- Does cell position influence commitment?
- Are different commitment states linked to different terminal differentiation outcomes?
I thought this was an outstanding talk, one of the best at the meeting.