Induction of the core-MHB cascade is regulated by several factors. Once the presumptive MHB territory has been established, genes of the FGF, Wnt, Pax and Engrailed gene families (the core-MHB cascade) are rapidly induced within this region. FGF8 activity is critical, and expression and function of this molecule are regulated by miR-9 and members of the Notch pathway (Serrate, Hairy, Lunatic Fringe and Delta1). The interplay between members of the core-MHB cascade begins, and this is regulated by Lrrn1, Grg4 and XHR1 at multiple levels within the cascade. Specific interactions between members have also been described, notably RPTPλ-mediated activation of Wnt1 following FGF8 stimulation and the transcription of Engrailed 2a by FGF8-mediated activation of grhl2b