Ectopic expression of Hoxb1 induces cardiac and craniofacial malformations

Members of the large family of Hox transcription factors are encoded by genes whose tightly regulated expression in development and in space within different embryonic tissues confer positional identity from the neck to the tips of the limbs. Many structures of the face, head and heart develop from cell populations expressing few or no Hox genes. Hoxb1 is the member of its chromosomal cluster expressed in the most rostral domain during vertebrate development, but never by the multipotent neural crest cell population anterior to the cerebellum. We have developed a novel floxed transgenic mouse line, CAG-Hoxb1,-EGFP (CAG-Hoxb1), which upon recombination by Cre recombinase conditionally induces robust Hoxb1 and eGFP over-expression. When induced within the neural crest lineage, pups die at birth. A variable phenotype develops from E11.5 on, associating frontonasal hypoplasia/aplasia, micrognathia/agnathia, major ocular and forebrain anomalies, and cardiovascular malformations. Neural crest derivatives in the body appear unaffected. Transcription of effectors of developmental signaling pathways (Bmp, Shh, Vegfa) and transcription factors (Pax3, Sox9) is altered in mutants. These outcomes emphasize that repression of Hoxb1, along with other paralog group 1 and 2 Hox genes, is strictly necessary in anterior cephalic NC for craniofacial, visual, auditory and cardiovascular development. Footnotes * Numerous typos and rewording in text addressed. Also: Line 201-209: Added paragraph "Fgf8, encoding an important secreted growth factor needed for multiple processes of craniofacial development..." Line 283-291/292-303: Changed paragraph "Fgf8 is a known survival factor [...] could be distinguished with an appropriate antibody developed for chromatin immunoprecipitation." to "Hoxb1 overexpression in the NC lineage drastically decreases Bmp2 and Bmp4 transcription [...] effectors of the dramatic facial hypoplasia observed in severe mutant phenotypes." Line 425-426: Added "hyaloid" Line 427: Removed "Furthermore, altering adhesion complex signaling pathways in ocular NCC induces major developmental malformations of eye, specifically in the anterior segment (Tian, Sanders, Reynolds, van Roy, & van Hengel, 2012), while" Line 456: Added "RosatdT [Gt(ROSA)26Sortm9(CAG-tdTomato)Hze]" Line 493-497: Added paragraph about in situ hybridization method used Line 519: Added acknowledgements Line 778: Moved previous parts g and h to parts e and f, removed the word "laterally", substi