Isolation and analysis of pluripotent, parasitic stem cells

Why is there an allorecognition system in Botryllus? The answer can be found by following the fate of two compatible colonies after they fuse their vasculatures. After fusion, blood-borne germline and somatic (and/or pluripotent) stem cells can transfer between colonies and have the ability to expand and differentiate in their vascular partner.

This can often result in a situation where only one of the genotypes is represented in the gametic output of the fused individuals, a situation which will remain constant for life. This phenomenon, called stem cell parasitism (SCP) is a repeatable and heritable trait, and we have identified winner and loser genotypes among both laboratory-reared and natural populations. Parasitism also occurs in somatic cells, although it is a less predictable process.

This parasitism provides an excellent model to identify stem cells. We have identified GCP winner and loser genotypes within our inbred Botryllus lines. This will allow us to take a forward genetic approach to identify genes controlling this process, as was done to successfully identify the FuHC. In addition, we are isolating these stem cells using classic transplantation and reconstitution studies. Currently, we have enriched the stem cells responsible using FACS to a limiting dilution of 25-50 cells, and are in the process of creating reagents to further prospectively isolate these cells. How does one stem cell out-compete another stem cell? Whatever the reason, it will reveal important and fundamental characteristics of stem cells, and is experimentally accessible in Botryllus.