A. Giannattasio, G. Angeletti, M. De Rosa, et al.
DISCUSSION
not only caspase 3 expression but also the expression of
all caspases is different before and after puberty in rat testis
and/or in pathological conditions that lead to an increased
cell apoptosis.
Proteins of the Bcl-2 family are important regulators of
apoptosis in many tissues of the embryo and adult. The re-
cently isolated bcl-w gene encodes a pro-survival member of
Bcl-2 family, which is widely expressed. Mice that lack Bcl-
W are apparently normal; most tissues exhibited normal
histology, and hematopoiesis is unaffected. Although female
reproductive function is normal, the males are infertile (11).
The number of both Sertoli and germ cells is reduced, with
elongating spermatids and spermatozoa the most severely
affected. Recent data indicate that bcl-w, in wild Type mice,
is primarily expressed in immature germ cells, and in Sertoli
cells but not in Leydig cells. The first phase of spermatoge-
nesis, between birth and 5 weeks of age, is normally ac-
companied by massive physiological apoptosis of germ cells,
to adjust the number so that Sertoli cells correctly support
them. Therefore, during this phase of spermatogenesis, pro-
apoptotic proteins prevail on anti-apoptotic proteins. The
adult spermatogenesis is critically dependent on anti-apop-
totic proteins, such as bcl-w. Moreover, the reduction in
the number of Sertoli cells involves an up-regulation of Fas-
Ligand (Fas-L) in these cells with a consequent reduction
in the number of germ cells to establish a new balance be-
tween Sertoli and germ cells (12). In this study, we demon-
strate that bcl-w mRNA is expressed in isolated Sertoli cells
of pre-puberal rat testes. By considering the role of Sertoli
cells during murine spermatogenesis, further studies are
required to understand the role of bcl-w in the programmed
cell death of both Sertoli and germ either cells before or af-
ter puberty or in specific experimental conditions, such as
hypophysectomy, that determine an increase of apoptosis
in the seminiferous tubules. Moreover, the remarkable
spermatogenic defect in mice creates the possibility that
mutations in the bcl-w gene might have a key role in the
ethiopathogenesis of male infertility (1). The ICE (Inter-
leukin-1ꢀ converting enzyme) family, recently termed cas-
pases, plays a basic role in the apoptotic pathway. Caspases
normally exist in cells as inactive pro-enzymes and can be
activated by 2 distinct mechanisms: the FADD/caspase 8
cascade, and the Apaf-1/caspase 9 cascade. These two
mechanisms are used extensively by cells for the activation
of the effectors caspases: caspase 3, caspase 6, and/or cas-
pase 7. Caspases, then, cleave and activate different pro-
teins important for the signal transduction pathways con-
trolling cell growth and function (13). Our preliminary re-
sults demonstrate that isolated Sertoli cells of pre-puberal
rat testes express caspase 3. This finding might be crucial in
clarifying whether Sertoli cells die by an apoptotic mecha-
nism. Further studies are required to understand whether
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