Mk. Byeon et al., NCAM POLYPEPTIDES IN HEART DEVELOPMENT - ASSOCIATION WITH Z-DISKS OF FORMS THAT CONTAIN THE MUSCLE-SPECIFIC DOMAIN, The Journal of cell biology, 128(1-2), 1995, pp. 209-221
Previous studies of neural cell adhesion molecule (NCAM) cDNAs have re
vealed an alternatively spliced set of small exons (12A, 12B, 12C, and
12D) that encode a region in the extracellular portion of the molecul
e known as the muscle-specific domain (MSD). The entire MSD region can
be expressed in skeletal muscle, heart, and skin; only exons 12A and
12D have been found in brain. These studies did not reveal which NCAM
polypeptides contain the MSD region or the immunohistochemical distrib
ution of these NCAM molecules. To address these questions, we prepared
antibodies against the oligopeptides encoded by exons 12A and 12B and
by exons 12C and 12D, and we used these antibodies to study the forms
of NCAM containing the MSD region expressed during embryonic chicken
heart development. These antibodies recognize certain forms of NCAM fo
und in the heart, but they do not recognize brain NCAM. In the heart,
each of the splice variants of NCAM (large cytoplasmic domain, small c
ytoplasmic domain, and small surface domain) that differ in their mode
of attachment to the plasma membrane or in the size of their cytoplas
mic domain is expressed in a form that contains and in a form that lac
ks the MSD region. No microheterogeneity is observed in the size of NC
AM molecules containing the MSD region, even at the level of cyanogen
bromide fragments, suggesting that exons 12A-D are expressed as a sing
le unit. Depending on the site and the stage of development, the perce
nt of NCAM molecules containing the MSD region can vary from nearly 0
to 100%. In general, this percentage increases during development. In
immunohistochemical studies of hearts from stage 18 embryos, forms of
NCAM containing the MSD region colocalized with Z discs. No other adhe
sion molecules were found in this distribution at this early stage of
development. Studies on isolated cells in vitro demonstrate that the c
olocalization with Z discs of NCAM molecules containing the MSD region
does not depend on cell-cell contact, and they raise the possibility
that this form of NCAM is involved in cell-extracellular matrix intera
ctions. The association of NCAM molecules containing the MSD region wi
th Z discs suggests that this form of NCAM is involved in early myofib
rillogenesis.