Fig. 1. Gas1 transcripts are detected in developing limbs. Expression of Gas1 was examined by ISH. (A-C) Dorsal view of the forelimbs at E9.25, E9.5 and E10.5. Anterior (a) is at top and posterior (p) at bottom; flb, forelimb bud. Gas1 is expressed in the lateral plate mesoderm and asymmetrically in the limbs with higher levels anteriorly. (D-G) Whole-mount ISH of E11.5-E14.5 forelimbs shows expression in the autopod (dorsal view, anterior at top). White arrowheads indicate the interdigital regions; open arrowheads, perichondorgenic regions; asterisks, joints or prospective joints. (H-K) ³⁵S-ISH of E10.5-E15.5 forelimbs (horizontal sections, anterior at top). (H) Superimposed images from adjacent sections of E10.5 Gas1 expression (red) in anterior two-thirds of the mesenchyme but not in AER (visualized by Fgf8 expression (green) in the adjacent section). At E12.5 (I), Gas1 transcripts (pink granules) are prominent in the prechondrogenic region (black arrowheads) and the interdigits (white arrowheads). At E13.5 (J), Gas1 is expressed in the interdigits (much weaker than at E12.5) and prospective joints (asterisks). At E15.5 (K), Gas1 is localized to perichondrium lining the joint cavities (asterisks).