A systems-level approach reveals new gene regulatory modules in the developing ear.

The inner ear is a complex vertebrate sense organ, yet it arises from a simple epithelium, the otic placode. Specification towards otic fate requires diverse signals and transcriptional inputs that act sequentially and/or in parallel. Using the chick embryo, we uncover novel genes in the gene regulatory network underlying otic commitment and reveal dynamic changes in gene expression.

Stage-dependent plasticity of the anterior neural folds to form neural crest.

The anterior neural fold (ANF) is the only region of the neural tube that does not produce neural crest cells. Instead, ANF cells contribute to the olfactory and lens placodes, as well as to the forebrain and epidermis. Here, we test the ability of the ANF to form neural crest by performing heterotopic transplantation experiments in the chick embryo.

Identification and dissection of a key enhancer mediating cranial neural crest specific expression of transcription factor, Ets-1.

Neural crest cells form diverse derivatives that vary according to their level of origin along the body axis, with only cranial neural crest cells contributing to facial skeleton. Interestingly, the transcription factor Ets-1 is uniquely expressed in cranial but not trunk neural crest, where it functions as a direct input into neural crest specifier genes, Sox10 and FoxD3. We have isolated and interrogated a cis-regulatory element, conserved between birds and mammals, that drives reporter expression in a manner that recapitulates that of endogenous Ets-1 expression in the neural crest.

Pax2 and Pea3 synergize to activate a novel regulatory enhancer for spalt4 in the developing ear.

The transcription factor spalt4 is a key early-response gene in otic placode induction. Here, we characterize the cis-regulatory regions of spalt4 responsible for activation of its expression in the developing otic placode and report the isolation of a novel core enhancer. Identification and mutational analysis of putative transcription factor binding sites reveal that Pea3, a downstream effector of FGF signaling, and Pax2 directly activate spalt4 during ear development.

Gain- and loss-of-function approaches in the chick embryo.

The chicken embryo has been used as a classical embryological model for studying developmental events because of its ready availability, similarity to the human embryos, and amenability to embryological and surgical manipulations. With the arrival of the molecular era, however, avian embryos presented distinct experimental limitations, largely because of the difficulty of performing targeted mutagenesis or transgenic studies. However, in the last decade and a half, a number of new methods for transient transgenesis have been developed that allow efficient alteration of gene function during early embryonic development.