Spermatogonial Stem Cell Transplantation and Culture - Male Germline Stem Cells Developmental and Regenerative Potential - page 112

Fig. 5.2 Examples of recipient testes transplanted with various transgenic donor cells.
( a ) Immunodeficient nude mouse recipient transplanted with LacZ positive rat cells. Blue colonies
from donor-derived stem cells are clearly visible. Scale bar = 2 mm. ( b ) Immunocompatible
recipient transplanted with both GFP ( green ) and DS-Red ( red ) mouse donor cells. Individual
spermatogonia can be seen on the basement membrane of the recipient seminiferous tubules. Scale
bar = 140 mm

of enrichment (Ebata et al. 2005 ). For example, Gfra1 has been considered a puta-
tive marker for the SSC population. Selection of Gfra1 positive cells from neonatal
mouse pups has been reported to enrich for SSCs approximately 1.8-2.5-fold; how-
ever, selection of Gfra1 positive cells from adults actually depletes the positive
population to only 13% of the nonselected population (Hofmann et al. 2005a, b ;
Buageaw et al. 2005 ). Interestingly, when applied to rat pups, we have observed an
over 60-fold increase in SSCs in the Gfra1 positive population (Schmidt et al. 2008 ,
unpublished).

5.2.5.2 Homing Efficiency

The ability of a specific stem cell to home to a particular niche is a hallmark of adult
stem cell transplantation techniques. Little research has examined this phenomenon
outside of the hematopoietic system, owing in part to an inability to study directly
the stem cell in the niche. In the hematopoietic stem cell system, homing is a rapid
process, thought to take less than 2 days, that is dependent on a variety of compo-
nents including chemokines, cell adhesion, and extracellular matrix molecules
(Lapidot et al. 2005 ). The ability of the SSC to home to the SSC niche is essential
for transplanted SSCs to colonize and undergo spermatogenesis in the recipient
testis. For the recipient Sertoli cell to recognize and initiate homing of the SSC to