ISOLATION OF NOVEL TISSUE-SPECIFIC GENES FROM CDNA LIBRARIES REPRESENTING THE INDIVIDUAL TISSUE CONSTITUENTS OF THE GASTRULATING MOUSE EMBRYO

A total of 5 conventional, directionally cloned plasmid cDNA libraries have been constructed from the entire embryonic region of the mid-gas trulation mouse embryo and from its four principal tissue constituents (ectoderm, mesoderm, endoderm and primitive streak). These libraries have been validated with respect to the number of independent clones, insert-size and appropriate representation of diagnostic marker genes, Subtractive hybridisation has been used to remove clones common to th e Endoderm and Mesoderm cDNA libraries resulting in an Endoderm minus Mesoderm subtracted library, probe prepared from this subtracted libra ry has been hybridised to a grid containing approximately 18,500 Embry onic Region library clones, Three novel clones have been recovered as well as expected genes already known to be highly expressed in the pri mitive endoderm lineage at this stage of development, In situ hybridis ation to early postimplantation embryos has revealed the expression pa tterns of these novel genes, One is highly expressed exclusively in vi sceral endoderm, one is expressed in ectodermal and endodermal tissues , and the third proves to be an early marker of prospective and differ entiated surface ectoderm as wed as being expressed in endoderm and it s derivatives.