The Cnidarian, hydra, lends itself to studies related to the role of e
xtracellular matrix (ECM) components in development because of its hig
h regenerative capacity and its simple structure, which is organized a
s an epithelial bilayer with an intervening ECM termed the mesoglea. P
revious immunocytochemical and biochemical studies have established th
at hydra mesoglea contains many of the major matrix components (e.g.,
fibronectin, laminin, type IV collagen, and heparan sulfate proteoglyc
an) associated with the ECM of vertebrate and more complex invertebrat
e species. Additional studies have also established that ECM component
s have a critical role in hydra development as monitored during head r
egeneration and morphogenesis of hydra cell aggregates. In the present
study a monoclonal antibody (mAb52) raised to isolated hydra mesoglea
was used as a probe in additional functional studies and to screen a
cDNA expression library made from poly(A)(+) RNA isolated from Hydra v
ulgaris. Immunofluorescent analysis indicated that mAb52 was localized
along the entire longitudinal axis of adult polyps in what is termed
the subepithelial zones of hydra mesoglea. Cytochemical studies found
these subepithelial zones to be rich in anionic sites. Previous studie
s have shown that mAb52 blocks hydra cell aggregate development and ex
periments in the current study have shown that mAb52 also blocks in vi
vo interstitial cell (I-cell) migration in hydra grafts. Sequence anal
ysis of cDNA clones isolated using mAb52 indicated that the protein en
coded by these clones had structural homology with mammalian and Droso
phila laminin B1 chain and hybridized to a single 6.75-kb band on Nort
hern blots of total hydra RNA. One interesting difference in hydra lam
inin B1 was the presence of a FTGTQ amino acid sequence in place of th
e vertebrate YIGSR cell binding domain. Under nonreducing conditions,
polyclonal antibodies against FTGTQ bound to the same >200-kDa band on
Western blots of mesoglea as mAb52 and also immunolocalized to the su
bepithelial zones. Under reducing conditions, anti-FTGTQ antibodies bo
und to a single band with a mass of approximately 200 kDa. In addition
, FTGTQ peptide inhibited adhesion of dissociated hydra cells to mesog
lea and anti-FTCTQ antibodies inhibited hydra cell binding to substrat
es coated with mesoglea or FTGTQ peptide. Anti-FTGTQ antibodies also i
nhibited in vivo I-cell migration in hydra grafts. Given the early div
ergence of Cnidarians during evolution, these studies indicate the hig
hly conserved nature of laminin and provide additional information reg
arding the critical role of ECM components during hydra development. (
C) 1994 Academic Press, Inc.