Biomedical Engineering Reference
In-Depth Information
5.2.3
Clonality and Quantification
An interesting and useful characteristic of colonization of recipient seminiferous
tubules by donor SSCs is that when transplanted at the right concentration, distinct
colonies of donor-derived spermatogenesis are formed. Colonies of spermatogenesis
can be easily identified if the donor recipient is transgenic for a marker such as
b-galactosidase (LacZ) or green fluorescent protein (GFP). When SSCs are trans-
planted into recipient testes at low concentrations, each colony is theoretically
derived from a single SSC and quantification of colonies is directly related to the
number of stem cells in the initial population (Dobrinski et al.
1999b
; Nagano et al.
1999
; Kanatsu-Shinohara et al.
2006
). This relationship allows for the quantifica-
tion of SSCs in populations of cells from various experiments and has been used to
identify molecules useful for SSC enrichment.
5.2.4
Species Specificity
5.2.4.1
Rodent
The classical species that has been used to study the SSC is the mouse.
Transplantation of mouse SSCs into infertile mouse recipients results in robust
spermatogenesis that can lead to the production of donor-derived offspring through
natural mating of the recipient or intracytoplasmic sperm injection (Brinster and
Avarbock
1994
). However, because the SSCs reside in the basal compartment of the
seminiferous tubule, which is on the blood side of the blood-testis barrier, immune-
compatible donors and recipients must be used. Alternatively, animals with natu-
rally or artificially depressed immune systems can also be used for recipients.
The rat SSC has also received much attention in the field. Like in mice, trans-
plantation of rat SSCs into an immunologically compatible recipient results in the
production of fully functional spermatozoa (Ryu et al.
2003
). Additionally, xenotrans-
plantation of rat SSCs into mouse recipients also results in complete spermatogenesis
(Clouthier et al.
1996
). When rat SSCs are transplanted into mouse recipient testes,
the pattern of germ cell development (cycle of the seminiferous epithelium) follows
that of the rat, indicating that the mechanisms and timing of germ cell development are
intrinsic to the germ cell and not directed by the somatic environment (Franca et al.
1998
).
5.2.4.2
Non-rodents
SSCs from every species examined have the ability to colonize the basement
membrane of the mouse seminiferous tubule after xenotransplantation; however,
only rodent SSCs are able to undergo complete spermatogenesis, indicating that
species specific mechanisms regulating SSC differentiation exist (Clouthier et al.
1996
; Dobrinski et al.
1999a, 2000
; Nagano et al.
2001, 2002
; Oatley et al.
2004
).
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