Fig. 8: Misexpression of iCreb5-HA^(Prx1-Cre) promotes formation of a Fat4⁺, Wnt5a⁻ perichondrium.

Gene expression assayed by RNAscope FISH in the hindlimbs of an E14.5 Creb5^Δ9/Δ9 embryo or control littermate (a) or in serial sections of the forelimbs of an E14.5 Prx1-Cre-iCreb5 embryo or control littermate (b, c). In control limbs, the Fat4^high, Wnt5a^low articular perichondrium (yellow arrows) and Fat4^low, Wnt5a^high metaphyseal/diaphyseal perichondrium (white arrows) are indicated. In Creb5^Δ9/Δ9 mutant limbs, the perichondrial cells expressing both Wnt5a and mutant Creb5^Δ9/Δ9 (white arrowheads) are indicated. In Prx1-Cre-iCreb5 limbs: Fat4^low, Wnt5a^high perichondrium (white arrowheads) or Fat4^high, Wnt5a^low perichondrium (yellow arrowheads) are indicated. In Prx1-Cre-iCreb5 embryos, perichondrial expression of iCreb5-HA^(Prx1-Cre) promotes high level expression of Fat4 in the perichondrium, blocks expression of Wnt5a in this same tissue (yellow arrowheads) and inhibits chondrocyte hypertrophy. Perichondrium surrounding cartilage elements that display chondrocyte hypertrophy in Prx1-Cre-iCreb5 embryos continue to express WT levels of Wnt5a (white arrowheads). Similar results were obtained in two independent biological repeats. Scale bar equals 200 microns.