the vertebrae and limbs hnrnp a1 protein is initially present in precartilage cell condensations and persists in early chondrocytes earlier studies have looked at the distribution of hnrnp a1 in various differentiated cell types as well as in developing germ line cells of postnatal mice faura et al 1995 kamma et al 1995 these studies demonstrated that hnrnp a1 was expressed at higher levels in earlier stages of spermatocyte development kamma et al 1995 the studies described in this thesis represent the first systematic analysis of hnrnp a1 39 s expression during embryogenesis the functional significance of the stage dependent hnrnp a1 expression patterns seen during development is dependent in part on the role of this protein in alternative splicing one developmentally important gene whose transcript is alternatively spliced with the participation of hnrnp a1 is fibroblast growth factor receptor 2 fgfr2 where it is involved in the choice of exon 9 rather than exon 8 del gatto konczak et al 1999 because i fgfr2 has a known pattern of spatiotemporal expression during appendicular chondrogenesis peters et al 1992 lizarraga et al 1999 szebenyi and fallon 1999 ii incorrect exon 8 exon 9 choice in fgfr2 in humans has known morphological consequences to the limb skeleton oldridge et al 1999 and iii the studies described herein show hnrnp a1 to have a distribution in the developing limb coincident with that previously found for fgfr2 the remainder of the work described was directed towards testing whether interference with hnrnp a1 synthesis or function had the effects predicted on the basis of our.