Biology Reference
In-Depth Information
Davis
1995
). Confirmation that the sperm head remains adjacent to the centro-
some/midpiece is also demonstrated by absence of arrest during the first cell cycle
(Palazzo et al.
2000
). These observations are important in illustrating that it is
possible to replace the centrosome of one spermatozoon with that of another while
ensuring the effective reorientation and elongation of the microtubule array toward
the female pronucleus, which is known to be a good indicator of sperm aster
quality (Navara et al.
1996
). This observation naturally leads to considering the
potential of this approach as a therapeutic remediation strategy in certain cases of
male infertility. This prospect has already been proposed in humans with positive
results (Emery et al.
2004
). In the latter study, sperm heads detached from the
respective flagella were co-injected into oocytes which resulted in a normal
pregnancy. In our laboratory, we also envision substantial promise in centrosomal
replacement across spermatozoa from different species. For example, we have
studied sperm form and function in more than 25 felid species, many of which are
endangered and teratospermic (Pukazhenthi et al.
2006
). It would be intriguing to
determine if centrosomes transferred from a normospermic species to spermatozoa
from males that produce high proportions of malformed cells can be used to boost
fertility or genetic management of rare individuals or populations.
Lastly, improving the sperm selection before microinjection might be another
solution to avoid injecting cells with centrosomal issues. It is now possible to
predict centrosomal function on the basis of midpiece morphometry as measured
using a high magnification device. This process known as intracytoplasmic,
morphologically selected sperm injection (IMSI) has been reported in humans
(Ugajin et al.
2010
) and is under development in cats.
3.4.2 Centrosomal Maturation In Vitro
Given that centrosomal maturity and normal function are acquired as testicular
spermatozoa pass through the epididymis, then a priority is to learn significantly
more about maturational processes within this region. Our knowledge on this
subject is rudimentary for all species. For the cat, epididymal epithelial cells
secrete factors (including hypotaurine or alkaline phosphatase) that impart phys-
iological changes and could permit the sperm centrosome to complete maturation
(Axnér
2006
). However, a lack of information on specific mechanisms and pro-
teins has made it impossible to artificially mature testicular spermatozoa in vitro
for subsequent assisted reproduction use in any species. We are currently inves-
tigating centrosomal function and the presence of centriole maturation markers,
such as cenexin (Lange BM and Gull K
1995
) and speriolin (Goto et al.
2010
), in
spermatozoa isolated from different regions of the cat epididymis. We hope that
resulting knowledge can be used to develop in vitro maturation protocols that
could promote centrosomal maturation in testicular gametes and/or overcome
functional deficits in spermatozoa regardless of source.
