S. Damjanovski et al., TRANSIENT EXPRESSION OF SPARC IN THE DORSAL AXIS OF EARLY XENOPUS EMBRYOS - CORRELATION WITH CALCIUM-DEPENDENT ADHESION AND ELECTRICAL COUPLING, The International journal of developmental biology, 38(3), 1994, pp. 439-446
Our comprehension of the molecular mechanisms underlying embryogenesis
has been greatly enhanced by the identification and characterization
of associated extracellular matrix macromolecules. Using Xenopus laevi
s as a model, we investigated the expression and distribution of SPARC
(Secreted Protein, Acidic, Rich in Cysteine; also called osteonectin
and BM-40) during early embryonic development. SPARC has been found to
be enriched in tissues undergoing rapid morphological development, di
fferentiation, and remodeling. In Xenopus, SPARC transcripts are first
expressed by primordial cells which give rise to the first embryonic
tissues, the notochord and somites. SPARC RNA levels remained high thr
oughout the rapid morphological development and differentiation phase
of these tissues, and then rapidly decreased. Of particular interest,
SPARC protein began to accumulate within the intersomitic clefts at th
e onset of trunk myotome contraction. The intersomitic enrichment of S
PARC remained high as long as the myotomes remained electrically coupl
ed, principally by gap junctions. As myotomes became innervated, SPARC
expression decreased dramatically within the somites. SPARC was also
found to be enriched within other tissues, such as the neural tube and
epidermis. In addition, the selective spatial-temporal enrichment of
SPARC suggests it makes important calcium-dependent contributions to e
arly morphological development.