Shh, short for Sonic hedgehog, is a member of the hedgehog gene families. It plays a critical role in the embryonic development, with its signaling pathway being essential for various biological processes such as cell division, cellular differentiation, and maintaining neuronal integrity [2,5,6]. The Shh signaling pathway involves components like Smoothened (Smo) and Glioma-associated homolog (GLI), and its dysregulation can lead to multiple physiological changes [3,5].

In medulloblastoma, the SHH group is characterized by constitutive activation of the SHH signaling pathway, often due to mutations in PTCH1 or other downstream pathway mutations, making SHH inhibitors a clinical interest for treatment [1]. In asthma, Shh is involved in the pathogenesis, with recombinant Shh inducing CCL2 overexpression [2]. In autism spectrum disorder, dysregulation of SMO-SHH signaling contributes to the pathogenesis, leading to changes like increased oxidative stress [3]. In limb development, the SHH signaling pathway is crucial for proper limb skeleton formation and specifying digit identities, and its deregulation can cause congenital limb defects [4]. In the central nervous system development, Shh is essential for pattern formation, cell-fate specification, etc., and abnormal Shh signaling leads to nervous system diseases [6]. In adamantinomatous craniopharyngioma, inhibition of the SHH pathway has a protumourigenic effect [7]. In cochlear morphogenesis, Shh signaling is required, and mouse embryos lacking Shh or its essential signal transduction components display cochlear agenesis [8]. After ischemic stroke, Shh regulates M2 microglial polarization and fibrotic scar formation [9].

In conclusion, Shh is vital for embryonic development, especially in processes like limb development, central nervous system development, and cochlear morphogenesis. Its dysregulation is associated with various diseases such as medulloblastoma, autism, and certain pituitary tumors. Studies using gene knockout or conditional knockout mouse models (implicit in understanding its role when function is lost) have been crucial in revealing these functions and disease associations, providing insights for potential therapeutic interventions [1-9].