EXPRESSION OF THE MOUSE FIBRONECTIN GENE AND FIBRONECTIN-LACZ TRANSGENES DURING SOMITOGENESIS

Fibronectins (FNs) ape essential for the proper development of embryon ic mesenchymal tissues, A lacZ reporter gene has been fused to 4.9 kbp of DNA from the rat FN gene 5' flanking region, and this construct ha s been microinjected into fertilized mouse embryos to investigate the cis elements needed for the temporal and spatial regulation of FN in v ivo. Histochemical staining of embryos for beta-galactosidase activity demonstrated that four independent lines shared a specific pattern of lacZ expression, reflecting the activity of the fibronectin sequences contained within the transgene, Specifically, somites stained positiv ely for lacZ, but expression was spatially and temporally non-uniform, with higher levels in more caudal somites after a total of ca. 13 som ite pairs had formed, This rostral-caudal gradient of lacZ expression in somites of embryos beyond this stage resembled the distribution of endogenous FN mRNA, as detected by whole mount in situ hybridization, The transgene was not expressed in the developing heart where endogeno us FN mRNA was detected. Unexpectedly, highly localized staining was o bserved within the neural tube beginning at ca. E10-10.5, and two of t he lines exhibited additional areas of staining due to the individual integration sites. Thus, the 4.9 kbp FN fragment appears to recapitula te closely the complex pattern of FN expression observed during somito genesis. A smaller fragment of 0.9 kbp also directed lacZ expression i n caudal somites at E9.5, suggesting that these sequences are sufficie nt to establish the spatio-temporal pattern. (C) 1997 Wiley-Liss, Inc.