Developmental regulation and tissue‐specific localization of calmodulin mRNA in the protochordate Ciona intestinalis

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Abstract
A full‐length cDNA encoding a highly conserved calmodulin was isolated from a cDNA library prepared from hatched larvae of the ascidian Ciona intestinalis. Sequence analysis has identified a 447 b.p. open reading frame, encoding a putative protein of 149 amino acid residues, with a predicted molecular weight of 16.8 kDa, showing 85–98% identity to known calmodulins. Northern blot analysis revealed a single transcript of about 0.8 kb in length, which was maternally expressed and progressively increased during development, until late tail‐bud stage. Whole‐mount in situ hybridizations, carried out on embryos at different stages of development, showed that starting from the neurula stage, the C. intestinalis calmodulin (Ci‐CaM) expression became restricted to the neuroectoderm and that in larvae it was specifically detected in the nervous system.