Stem cell differentiation in vivo.


The big picture.

One of the central goals of regenerative medicine is to identify stem/ progenitor cells that will populate and repair damaged tissues when they are implanted into patients. These cells need to be able to adapt appropriately to the in vivo environment in order to be effective. Although our understanding of the genes and pathways involved with stem cell maintenance and differentiation has benefited greatly from in vitro studies, we have a very limited knowledge of stem cell biology in vivo. A better understanding of the behaviour of stem/precursor cells in vivo will allow us to predict how transplanted cells should behave when reintroduced during regenerative therapy. A better understanding of which genes mark adult stem cell populations will aid in harvesting the appropriate cells for use in therapy. A better understanding of all of the possible cell fates associated with expression of an individual marker will help to predict the differentiation potential of transplanted stem/progenitor cells. A better understanding of what drives stem cell replication and differentiation in vivo may help to create precursor cells that are more appropriately tailored to individual needs.


A wealth of ongoing research is focused on characterising stem cells, and in identifying the factors that regulate their self-renewal and differentiation, particularly in cell culture and in adult mammalian systems. However, in mammals in vivo characterisation of stem/progenitor cells is hampered by their limited numbers and locations in niches that are not readily accessible. In contrast, the zebrafish is a small vertebrate, with numerous populations of stem/progenitor cells. Throughout embryonic and early larval stages of development, stem/progenitor cell niches within the zebrafish can be visualised by high-resolution imaging, enabling approaches to study the events by which stem/progenitor cells replicate, migrate and differentiate in the living animal. The fish therefore provides an outstanding model, complementing mammalian models and in vitro analyses, in which to study stem and progenitor cells in the intact organism.


















Two zebrafish stained to show the bone in brown. This experiment

shows that treating embryos for 4 hours with retinoic acid (RA) results

in the loss of bone formation (red arrows) in larval fish.


Osteoblast differentiation in zebrafish.

We study a stem cell population called the neural crest. These cells can differentiate into many different cell types including muscle, cartilage, nerves and bone. In order to differentiate into a specific cell type, stem cells need to  receive signals which tell them what to do. For example, we have found that a signal called retinoic acid inhibits stem cells from differentiating into osteoblasts (osteoblasts are the cells which form bone). By analysing different signals we have been able to unravel a three-step pathway that leads to osteoblast formation.



Our model for the how different signals activate or inhibit stem

cells to form osteoblast cells in vivo.


The long-term aim of this project.

Although stem cells show great promise as tools for regenerative medicine, there are many gaps in our knowledge that still need to be filled. By understanding more about how stem cells differentiate in vivo, we hope to provide information that will lead to more effective and safer stem cell therapy in human patients.


Further reading:

Hedgehog signalling is required for perichondral osteoblast differentiation in zebrafish.

Regulation of neural crest cell fate by the retinoic acid and Pparg signalling pathways.

Tracking gene expression during zebrafish osteoblast differentiation.

 

Roehl Lab