Otx2 is a target of N-myc and acts as a suppressor of sensory development in the mammalian cochlea

Transcriptional regulatory networks are essential during the formation and differentiation of organs. The transcription factor N-myc is required for proper morphogenesis of the cochlea and to control correct patterning of the organ of Corti. We show here that the Otx2 gene, a mammalian ortholog of the Drosophila orthodenticle homeobox gene, is a crucial target of N-myc during inner ear development. Otx2 expression is lost in N-myc mouse mutants, and N-myc misexpression in the chick inner ear leads to ectopic expression of Otx2. Furthermore, Otx2 enhancer activity is increased by N-myc misexpression, indicating that N-myc may directly regulate Otx2. Inactivation of Otx2 in the mouse inner ear leads to ectopic expression of prosensory markers in non-sensory regions of the cochlear duct. Upon further differentiation, these domains give rise to an ectopic organ of Corti, together with the re-specification of non-sensory areas into sensory epithelia, and the loss of Reissner's membrane. Therefore, the Otx2-positive domain of the cochlear duct shows a striking competence to develop into a mirror-image copy of the organ of Corti. Taken together, these data show that Otx2 acts downstream of N-myc and is essential for patterning and spatial restriction of the sensory domain of the mammalian cochlea.

Establishment of a proneural field in the inner ear

Hair-cells, supporting cells and sensory neurons are the main specialized cell-types responsible for mechanotransduction in the inner ear. They derive from precursors expressing proneural genes and recent data has underlined the importance of SoxB1 genes as upstream activators of proneural genes during cranial placode development. Here we review the steps of establishing a proneural field and propose several models for how early otic regionalization into a proneural territory is achieved.

Haemophilus influenza sepsis and shock secondary to biliary infection in an adult

A 46-year-old woman was seen with biliary obstruction secondary to a pancreatic tumor. After undergoing a percutaneous liver biopsy, she became septic and went into shock. Haemophilus influenzae type be bacteremia and biliary infection were verified. With treatment, the patient recovered from the infection. Biliary infection by H influenzae is rare, and fulminant infections in adults are even more uncommon. Hazards of invasive diagnostic procedures in patients with obstructive jaundice are discussed.