Developmental defects affecting the heart and aortic arch arteries are a significant phenotype observed in individuals with 22q11 deletion syndrome and are caused by a microdeletion on chromosome 22q11. TBX1, one of the deleted genes, is expressed throughout the pharyngeal arches and is considered a key gene, when mutated, for the arch artery defects. Pax9 is expressed in the pharyngeal endoderm and is downregulated in Tbx1 mutant mice. We show here that Pax9-deficient mice are born with complex cardiovascular malformations that affect the outflow tract and aortic arch arteries with failure of the 3rd and 4th pharyngeal arch arteries to form correctly. Transcriptome analysis indicated that Pax9 and Tbx1 may function together, and mice double heterozygous for Tbx1/Pax9 presented with a significantly increased incidence of interrupted aortic arch when compared with Tbx1 heterozygous mice. Using a novel Pax9Cre allele, we demonstrated that the site of this Tbx1-Pax9 genetic interaction is the pharyngeal endoderm, therefore revealing that a Tbx1-Pax9-controlled signalling mechanism emanating from the pharyngeal endoderm is required for crucial tissue interactions during normal morphogenesis of the pharyngeal arch artery system.

Small cell carcinoma/neuroendocrine carcinoma (SCNEC) of the oropharynx is uncommon. Recently, an association has been reported between oropharyngeal SCNEC and high-risk human papillomavirus (HPV) infection. While HPV infection confers a better prognosis for oropharyngeal squamous cell carcinoma, HPV infection does not appear to influence the biological behaviour of SCNECs, which are generally associated with poor clinical outcomes. We document two cases of SCNEC arising in the oropharynx with evidence of high-risk HPV infection. The cases highlight the expanding range of malignant oropharyngeal neoplasms that harbour oncogenic HPV infection and support the concept that, irrespective of HPV infection, neuroendocrine differentiation portends a poor prognosis.

Developmental defects affecting the heart and aortic arch arteries are a key phenotype observed in DiGeorge syndrome patients and are caused by a microdeletion on chromosome 22q11. Heterozygosity of TBX1, one of the deleted genes, is expressed throughout the pharyngeal arches and is considered a key component for the arch artery defects. Pax9 is expressed in the pharyngeal endoderm and is downregulated in Tbx1 mutant mice. We show here that Pax9 deficient mice are born with complex cardiovascular malformations affecting the outflow tract and aortic arch arteries with failure of the 3rd and 4th pharyngeal arch arteries to form correctly. Transcriptome analysis indicated that Pax9 and Tbx1 may function together, and mice double heterozygous for Tbx1/Pax9 presented with a significantly increased incidence of interrupted aortic arch when compared to Tbx1 heterozygous mice. Using a novel Pax9Cre allele we demonstrated that the site of this Tbx1-Pax9 genetic interaction is in the pharyngeal endoderm, therefore revealing that a Tbx1/Pax9-controlled signalling mechanism emanating from the pharyngeal endoderm is required for critical tissue interactions during normal morphogenesis of the pharyngeal arch artery system.Summary statementPax9 is required for outflow tract and aortic arch development, and functions together with Tbx1 in the pharyngeal endoderm for 4th arch artery formation.

Animals homozygous for the recessive, pleiotropic, mutation hpy (hydrocephalic-polydactyl) progressively lag behind their wild-type litter-mates in increase in body weight and brain dry weight over the period from 1-40 days post-partum; many homozygotes die within the first 14 days after birth. Light microscope observations of serial sections of brains revealed a mild to severe dilation of the entire ventricular system and damaged ependyma. Ciliated ependymal cells appeared reduced in number and destruction of ependymal cells over wide areas of the ventricular surfaces was observed. Preliminary scanning electron microscope studies confirmed the light microscope observations and revealed large numbers of erythrocytes and phagocytes associated with the ependymal surface. Neither the histological studies nor experiments involving intracerebral injections of tracer dyes demonstrated obstruction or stenosis of the aqueduct of Sylvius. Individual neurons appeared to be present in normal numbers and to be developing normally and at the same rate as in wild-type animals.