Biomedical Engineering Reference
In-Depth Information
Chapter 4
Morphometric Description of Spermatogonial
Stem Cells and Expansion of Their Clonal
Derivatives
Dirk G. De Rooij
Abstract
Spermatogonial stem cells (SSCs or A
s
spermatogonia) in rodents and
rams are single cells that can self-renew or form a pair (A
pr
) that will continue to
differentiate and form chains of A
al
spermatogonia. A
al
spermatogonia differentiate
into A1 spermatogonia that after six divisions produce spermatocytes via A2, A3,
A4, In, and B spermatogonia. The cell cycle times of each of the generations of
A1-B spermatogonia are similar and are about 14% of the duration of the epithe-
lial cycle. In contrast, the cell cycle times of the A
s,pr,al
spermatogonia are highly
variable, the minimal cell cycle time being about 30% longer than that of the A1-B
spermatogonia. During the epithelial cycle the A
s,pr,al
spermatogonia start to prolifer-
ate at about stage X and the A
pr
and A
al
spermatogonia stop dividing around stage II,
while the SSCs continue to proliferate until stage VI. There is a feedback regulation
between the numbers of A1-B spermatogonia and the length of the proliferative
period of the A
s,pr,al
spermatogonia. When the number of A1-B spermatogonia is
low, the A
s,pr,al
spermatogonia continue to proliferate longer. The A
s,pr,al
spermatogo-
nia in different epithelial areas produce variable numbers of A1 spermatogonia but
always more than needed, subsequently the surplus of A2-A4 will enter apoptosis,
ensuring an even distribution of germ cells from In spermatogonia onwards.
Keywords
Spermatogenesis • Spermatogonial stem cells • Spermatogonia • Cell
kinetics • Differentiation • Self-renewal
D.G. De Rooij (
*
)
Center for Reproductive Medicine, Academic Medical Center, University
of Amsterdam, Amsterdam, The Netherlands
and
Department of Endocrinology and Metabolism, Faculty of Science, Utrecht University,
3584 CH Utrecht, The Netherlands
e-mail: d.g.derooij@amc.uva.nl
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