Gail D. Burd
Ph. D., University of North Carolina
E-mail: gburd@email.arizona.edu
Research Interest:
Development of the olfactory system; Genes invloved in neural development; Role of sensory afferents and hormones in olfactory system development.
Research in my laboratory is focused on identifying factors that regulate or stimulate development of nervous system, with an emphasis on development of peripheral and central olfactory neurons in the frog, Xenopus laevis. Our research interests are quite broad and include interests in gene expression and regulation, cellular and tissue differentiation, and neural plasticity induced by hormones and by cellular interactions between afferent axons and target neurons.
In adult vertebrates, the olfactory receptor neurons are located in the nose in the olfactory epithelium. Axons of the olfactory receptor neurons project to the rostral tip of the brain and innervate their target, the olfactory bulb. During development, the olfactory epithelium is derived from two thickenings in the sense plate region of the head ectoderm, the olfactory placodes. Our cell lineage analysis has shown that the olfactory placodes originate from the anterior neural ridge, a ring of tissue that surrounds the anterior rim of the neural plate. We also have shown that the olfactory placodes can regenerate, if removed, and the new placode cells are derived from adjacent sense plate cells. In other studies, we examined gene expression for two genes, Pax-6 and Xenopus Distal-less3, that are expressed in cells derived from the anterior neural ridge and in cells of the olfactory placodes. Expression patterns for two other genes, Notch and Delta, also have been studied during olfactory placode development. We are currently testing whether these genes are involved in differentiation of the olfactory placodes. In addition, we identified two transcripts of Pax-6 with different 3' transcriptional activation domains, and are testing to see if these transcripts have different spatial or temporal patterns of expression and different functions in neural differentiation.
Most amphibians, including Xenopus, have a second stage of development stimulated by thyroid hormone secretion during metamorphosis. Prior to metamorphosis, there are two different types of olfactory epithelium located in the principal cavity and in the vomeronasal cavity. During metamorphosis, a third new area of olfactory epithelium develops de novo in the middle cavity and the principal cavity epithelium undergoes major cellular transformations. We have shown that these changes can be induced early by thyroid hormone. Further, using in situ hybridization we have shown that Pax-6, Notch and Delta, are expressed in the developing middle cavity epithelium and might be necessary for cellular differentiation of this tissue. Coincident with cellular changes in the olfactory epithelium, we have observed that drastic remodeling and growth occurs in the olfactory bulb. Principal cavity afferent axons are redirected to dorsal regions of the olfactory bulb at the time when all of the neurons in the dorsal olfactory bulb are born. We have shown that principal cavity afferents perform this redirection of projections to the dorsal bulb even in the absence of competition from middle cavity afferents in the ventral bulb. Experiments are in progress to test whether the principal cavity afferents or direct action of thyroid hormone is the stimulus for neurogenesis in the dorsal olfactory bulb.
Selected Publications:
Franco MD, Pape MP, Swiergiel JJ, Burd. Differential and overlapping expression patterns of X-dll3 and Pax-6 genes suggest distinct roles in olfactory system development of the African clawed frog Xenopus laevis. J Exp Biol. 2001 Jun;204(Pt 12):2049-61.
Higgs DM, Burd GD. Neuronal turnover in the Xenopus laevis olfactory epithelium during metamorphosis. J Comp Neurol. 2001 Apr 23;433(1):124-30.
Higgs DM, Burd GD. The role of the brain in metamorphosis of the olfactory epithelium in the frog, Xenopus laevis. Brain Res Dev Brain Res. 1999 Dec 10;118(1-2):185-95.
Petti MA, Matheson SF, Burd GD. Differential antigen expression during metamorphosis in the tripartite olfactory system of the African clawed frog, Xenopus laevis. Cell Tissue Res. 1999 Sep;297(3):383-96.
Burd GD, Sein V. Influence of olfactory innervation on neurogenesis in the developing olfactory bulb of the frog, Xenopus laevis. Ann N Y Acad Sci. 1998 Nov 30;855:270-3.
Hansen A, Reiss JO, Gentry CL, Burd GD. Ultrastructure of the olfactory organ in the clawed frog, Xenopus laevis, during larval development and metamorphosis. J Comp Neurol. 1998 Aug 24;398(2):273-88.
Reiss JO, Burd GD.Metamorphic remodeling of the primary olfactory projection in Xenopus: developmental independence of projections from olfactory neuron subclasses. J Neurobiol. 1997 Feb;32(2):213-22.
