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adding purified recombinant laminin fragments into Sertoli cell cultures
with an established TJ barrier, which was shown to disrupt the TJ barrier
in vitro via down-regulation of integral membrane proteins occludin and
JAM-A at the BTB, and similar observations were obtained by overexpress-
ing these laminin fragments in Sertoli cells (
Yan et al., 2008a
). Surprisingly,
laminin fragments were also found to reduce the level of β1-integrin at the
hemidesmosome (an intermediate filament based cell-matrix anchoring
junction present at the Sertoli cell-basement membrane interface) (
Yan
et al., 2008a
). A knockdown of β1-integrin at the hemidesmosome in Ser-
toli cell epithelium in vitro also led to a disruption of the TJ barrier via
redistribution of occludin and N-cadherin, with these proteins moved from
the cell-cell interface into the cell cytosol (
Yan et al., 2008a
), illustrat-
ing there is a functional link between the hemidesmosome and the BTB.
These findings thus illustrate that while spermiation and BTB restructuring
that take place at the opposite ends of the epithelium at stage VIII of the
epithelial cycle, they are functionally connected via the apical ES-BTB-
hemidesmosome axis. The presence of this axis was recently confirmed
by using a Sertoli cell injury model using phthalates, in which phthalate-
induced apical ES disruption that led to spermatid lose and accompanied
by a reducing level of laminins also induced a MMP-mediated BTB disrup-
tion (
Yao et al., 2009
,
2010
).
2.3. Gap Junctions
The building blocks of GJs are integral membrane proteins known as con-
nexins (Cx) such as Cx26, 33, 43. Six connexins form a hemichannel called
connexon
, and a connexon from one cell that docks with another connexon
of an apposing or adjacent cell forms a functional GJ (
Enders, 1993
;
Li
et al., in press
;
Pointis et al., 2010
). The primary function of GJs is to act
as communicating channels between neighboring cells for mediating cell-
cell communication for signal transduction (
Bosco et al., 2011
;
Giepmans,
2004
). In general, these channels allow diffusional exchange of ions and small
molecules that are <1 kD in size, however, GJs assembled by different con-
nexins indeed have variations among their pore size (
Bosco et al., 2011
;
Giepmans, 2004
). More than 20 connexins have been identified in rodent
and human genomes. GJ can be composed of homotypic or heterotypic
connexons, as such, a variety of GJs can be produced. Additionally, control
of passage of molecules across GJs can be further modulated in a connexin-
specific manner (
Bosco et al., 2011
;
Giepmans, 2004
). GJs can also interact
with AJs and TJs through the shared adaptor ZO-1. Thus, ZO-1 also link
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