The amiloride-sensitive epithelial sodium channel, ENaC, is a heteromultimeric protein made up of three homologous subunits (alpha, beta and gamma) (1,2). In vitro, assembly and expression of functional active sodium channels in the Xenopus oocyte is strictly dependent on alpha-ENaC--the beta and gamma subunits by themselves are unable to induce an amiloride-sensitive sodium current in this heterologous expression system (2). In vivo, ENaC constitutes the limiting step for sodium absorption in epithelial cells that line the distal renal tubule, distal colon and the duct of several exocrine glands. The adult lung expresses alpha, beta and gamma ENaC (3,4), and an amiloride-sensitive electrogenic sodium reabsorption has been documented in upper and lower airways (3-7), but it is not established whether this sodium transport is mediated by ENaC in vivo. We inactivated the mouse alpha-ENaC gene by gene targeting. Amiloride-sensitive electrogenic Na+ transport was abolished in airway epithelia from alpha-ENaC(-/-) mice. Alpha-ENaC(-/-) neonates developed respiratory distress and died within 40 h of birth from failure to clear their lungs of liquid. This study shows that ENaC plays a critical role in the adaptation of the newborn lung to air breathing.

Melanoma is one of the most aggressive cancers, and its incidence is increasing. These tumors derive from the melanocyte lineage and remain incurable after metastasis. Here we report that SONIC HEDGEHOG (SHH)-GLI signaling is active in the matrix of human hair follicles, and that it is required for the normal proliferation of human melanocytes in culture. SHH-GLI signaling also regulates the proliferation and survival of human melanomas: the growth, recurrence, and metastasis of melanoma xenografts in mice are prevented by local or systemic interference of HH-GLI function. Moreover, we show that oncogenic RAS-induced melanomas in transgenic mice express Gli1 and require Hh-Gli signaling in vitro and in vivo. Finally, we provide evidence that endogenous RAS-MEK and AKT signaling regulate the nuclear localization and transcriptional activity of GLI1 in melanoma and other cancer cells. Our data uncover an unsuspected role of HH-GLI signaling in melanocytes and melanomas, demonstrate a role for this pathway in RAS-induced tumors, suggest a general integration of the RAS/AKT and HH-GLI pathways, and open a therapeutic approach for human melanomas.cancer ͉ melanocyte ͉ hair follicle ͉ metastasis ͉ skin

Giant congenital naevi are pigmented childhood lesions that frequently lead to melanoma, the most aggressive skin cancer. The mechanisms underlying this malignancy are largely unknown, and there are no effective therapies. Here we describe a mouse model for giant congenital naevi and show that naevi and melanoma prominently express Sox10, a transcription factor crucial for the formation of melanocytes from the neural crest. Strikingly, Sox10 haploinsufficiency counteracts Nras(Q61K)-driven congenital naevus and melanoma formation without affecting the physiological functions of neural crest derivatives in the skin. Moreover, Sox10 is also crucial for the maintenance of neoplastic cells in vivo. In human patients, virtually all congenital naevi and melanomas are SOX10 positive. Furthermore, SOX10 silencing in human melanoma cells suppresses neural crest stem cell properties, counteracts proliferation and cell survival, and completely abolishes in vivo tumour formation. Thus, SOX10 represents a promising target for the treatment of congenital naevi and melanoma in human patients.

All pancreatic endocrine cells, producing glucagon, insulin, somatostatin, or PP, differentiate from Pdx1+ progenitors that transiently express Neurogenin3. To understand whether the competence of pancreatic progenitors changes over time, we generated transgenic mice expressing a tamoxifen-inducible Ngn3 fusion protein under the control of the pdx1 promoter and backcrossed the transgene into the ngn3(-/-) background, devoid of endogenous endocrine cells. Early activation of Ngn3-ER(TM) almost exclusively induced glucagon+ cells, while depleting the pool of pancreas progenitors. As from E11.5, Pdx1+ progenitors became competent to differentiate into insulin+ and PP+ cells. Somatostatin+ cells were generated from E14.5, while the competence to make glucagon+ cells was dramatically decreased. Hence, pancreas progenitors, similar to retinal or cortical progenitors, go through competence states that each allow the generation of a subset of cell types. We further show that the progenitors acquire competence to generate late-born cells in a mechanism that is intrinsic to the epithelium.

In human cutaneous malignant melanoma, a predominance of activated mutations in the N-ras gene has been documented. To obtain a mouse model most closely mimicking the human disease, a transgenic mouse line was generated by targeting expression of dominant-active human N-ras (N