INCREASED EXPRESSION OF LAMININ-1 AND COLLAGEN(IV) SUBUNITS IN THE AGANGLIONIC BOWEL OF 1S 1S, BUT NOT C-RET-/- MICE/

Extracellular matrix molecules, including laminin, affect the developm ent of enteric neurons and accumulate in the aganglionic colon of ls/l s mice, Quantitative Northern analysis revealed that mRNAs encoding th e beta 1 and gamma 1 subunits of laminin and collagens alpha 1(IV) and alpha 2(IV) are increased in the colons of ls/ls mice. Transcripts of laminin alpha 1 were evaluated quantitatively with reverse transcript ion and the competitive polymerase chain reaction (RT-cPCR). The abund ance of Laminin alpha 1 transcripts tvas developmentally regulated, bu t greater in the ls/ls than the wild-type colon at each age examined, In situ hybridization revealed that transcripts in the colon encoding laminin alpha 1 and beta and collagen alpha 2(IV) were initially expre ssed in the endoderm, but by E15, expression shifted to cells of the c olonic mesenchyme (ls/ls >wild type) where crest-derived cells migrate . The expression of laminin alpha 1 was examined in the totally agangl ionic intestine of E15 and newborn c-ret-/-mice, to determine whether an increase occurs when neurogenesis fails independently of the ls/ls defect. RT-cPCR revealed no difference from control in mRNA encoding l aminin alpha 1 in the c-ret-/-colon in either E15 or newborn animals, The accumulation of immunohistochemically demonstrable laminin that is prominent in the newborn ls/ls colon could not be detected in that of c-ret-/-animals. These observations suggest that transcripts encoding laminin-1 and collagen (IV) are increased in the colon and surroundin g pelvic mesenchyme of ls/ls mice because of an intrinsic lesion, rath er than a secondary consequence of aganglionosis. The data are compati ble with the hypothesis that the increased expression of laminin-1 con tributes to the failure of crest-derived cells to complete their colon ization of the ls/ls colon. (C) 1996 Academic Press, Inc.