Characterization of an extracellular matrix component specifically expressed in the basal lamina of the dorsal vessel in Drosophila melanogaster. D. Gratecos ¹, A. Chartier ¹, M. Astier ¹, S. Zaffran ², M. Semeriva ¹. 1) IBDM, LGPD, MARSEILLE, FRANCE; 2) Brookdale Center, NEW-YORK, USA.

   We have cloned a gene coding for a protein specifically expressed in the dorsal vessel and the oenocytes. The gene is transcribed into a 6 Kb mRNA. The longest cDNA isolated has an open reading frame encoding a 1729 amino acids long protein. This protein has no known homologue and contains in its N-terminal domain a putative signal sequence cleavage site and 35 highly similar repeated motifs rich in glycine and proline residues forming a collagen-like array. It is localized in the extracellular matrix (ECM) surrounding the pericardial cells and the dorsal vessel in a polarized distribution on the external face of the tube in close proximity to the ectoderm. The solubility properties of the protein as well as the presence of a RGD sequence in its C-terminal moiety are in good agreement with its location in the ECM. In mutant embryos which express neither the mRNA nor the protein, the pericardial cells appear detached from the dorsal vessel that is itself broken in some places. This new ECM component may play a role in the maintenance of the dorsal vessel or in the transmission of a signal from the ectoderm for the proper migration of the heart epithelium.