REGULATED EXPRESSION OF A NOVEL LAMININ BETA-SUBUNIT DURING THE DEVELOPMENT OF THE CHICK-EMBRYO

In order to define specific laminin variants implicated in organogenes is, we have undertaken a systematic search to detect and characterize novel laminin subunits, the expression of which is both developmentall y regulated and tissue-specific. cDNA prepared from embryonic chick ti ssues was amplified by the polymerase chain reaction (PCR) with degene rate primers based on conserved sequences in domains V and VI of membe rs of the laminin beta subunit family. Restriction mapping, cloning an d sequencing of PCR products demonstrated a novel cDNA, the derived pr otein sequence of which displayed greatest homology with laminin beta subunits. However, the degree of amino acid divergence, comparison of sequence motifs and pattern of expression indicates that the cloned cD NA does not code for the avian orthologue of a previously characterize d laminin beta subunit. Northern blot analysis showed that the express ion of the 6-kb mRNA coding for the novel subunit was restricted to th e skin. The mRNA was not detectable before day 5 of chick embryonic de velopment, after which in situ hybridization showed expression only in surface ectoderm cells and subsequently in the epidermis. The develop mentally regulated ectodermal expression of the novel beta subunit, pr ior to condensation of mesenchymal cells to form the dermis, is consis tent with a specific role for this laminin isoform in the development and maintenance of the skin.