Biomedical Engineering Reference
In-Depth Information
Fig. 8.1
Germline stem cell niche system in the
Drosophila
testis. (
a
) Structure of the male
reproductive system of the
Drosophila melanogaster
, in which the pair of testes are colored
yel-
low
. The distal blind tips (
rectangles
) include the niche structure that harbors the stem cells
(schematically shown in (
c
)). (
b
) A simplified model of a testis. Stem cells reside in the distal,
niche region (
green circle
), while differentiating cells are arranged toward the proximal opening
to outside the body. Thus, one can observe a polarity over the entire gonad (schematically shown
by the
arrow
). (
c
) Schematic of the stem cell niche system at the testis tip. A group of highly
specialized gonadal somatic cells, termed hub cells (
green
), comprise a niche to which germline
stem cells (
GSCs
) are attached. As a result of asymmetric division of a GSC, the cell that remains
in contact with the hub persists as a GSC, while the other that loses the contact becomes a gonial-
blast (
GB
), the first step in cell differentiation. As a result of the subsequent four synchronized
incomplete cell divisions of GB, two-, four-, eight-, and 16-cell cysts are formed; these intercon-
nected mitotic cells are termed spermatogonia or SG. The 16-cell cysts enter meiosis to form
haploid sperms.
Drosophila
testis also contains cystocytes ((
c
), shown in
light blue
), somatic cells
that support the differentiating germ cells. Cystocytes also have stem cells (cyst stem cells,
CySC
),
which are also in touch with and under the control of hub cells. (
a
,
c
), modified from Patterson
(
1943
) and Fuller and Spradling (
2007
), respectively, with permission
niche cells are established as a result of a programmed process of organogenesis
during the developmental stages (Kitadate et al.
2007
). In
Drosophila
germline,
mechanisms important for the maintenance of the stem cell niche system have been
revealed to a greater extent than any other systems. These include the contact
between a stem cell and the niche mediated by adhesion molecules such as cadherin,
Search WWH ::
Custom Search