ABSTRACT
Pyramidal neurons in the deep layers of the cerebral cortex can be classified into two major classes: callosal projection neurons and long-range subcortical neurons. We and others have shown that a gene expressed specifically by subcortical projection neurons, Fezf2, is required for the formation of axonal projections to the spinal cord, tectum, and pons. Here, we report that Fezf2 regulates a decision between subcortical vs. callosal projection neuron fates. Fezf2(-/-) neurons adopt the fate of callosal projection neurons as assessed by their axonal projections, electrophysiological properties, and acquisition of Satb2 expression. Ctip2 is a major downstream effector of Fezf2 in regulating the extension of axons toward subcortical targets and can rescue the axonal phenotype of Fezf2 mutants. When ectopically expressed, either Fezf2 or Ctip2 can alter the axonal targeting of corticocortical projection neurons and cause them to project to subcortical targets, although Fezf2 can promote a subcortical projection neuron fate in the absence of Ctip2 expression.
Subject(s)
Axons/metabolism , DNA-Binding Proteins/metabolism , Nerve Tissue Proteins/metabolism , Pyramidal Cells/metabolism , Repressor Proteins/metabolism , Tumor Suppressor Proteins/metabolism , Animals , DNA-Binding Proteins/genetics , Gene Expression Regulation/physiology , Mice , Mice, Mutant Strains , Nerve Tissue Proteins/genetics , Phenotype , Pyramidal Cells/cytology , Repressor Proteins/genetics , Tumor Suppressor Proteins/geneticsABSTRACT
The mammalian Olf1/EBF (O/E) family of repeated helix-loop-helix (rHLH) transcription factors has been implicated in olfactory system gene regulation, nervous system development and B-cell differentiation. Ebf (O/E1) mutant animals showed defects in B-cell lineage and brain regions where it is the only O/E family member expressed, but the olfactory epithelium appeared unaffected and olfactory marker expression was grossly normal in these animals. In order to further study the mammalian O/E proteins, we disrupted O/E2 and O/E3 genes in mouse and placed tau-lacZ and tau-GFP reporter genes under the control of the respective endogenous O/E promoters. Mice mutant for each of these genes display reduced viability and other gene-specific phenotypes. Interestingly, both O/E2 and O/E3 knockout mice as well as O/E2/O/E3 double heterozygous animals share a common phenotype: olfactory neurons (ORN) fail to project to dorsal olfactory bulb. We suggest that a decreased dose of O/E protein may alter expression of O/E target genes and underlie the ORN projection defect.
Subject(s)
Olfactory Receptor Neurons/metabolism , Transcription Factors/genetics , Animals , Genes, Reporter , Mice , Olfactory Receptor Neurons/cytology , Phenotype , Receptors, Odorant/metabolism , Recombinant Fusion Proteins , Transcription Factors/deficiency , Transcription Factors/metabolism , tau Proteins/genetics , tau Proteins/metabolismABSTRACT
The Olf-1/EBF (O/E) family of transcription factors plays important roles in neural development and B-cell maturation. We have utilized a variation of the direct selection scheme (Degenerate Oligo-based Direct Selection, or DODS) to identify a fourth member of the O/E family (O/E-4). We demonstrated that, similar to previously identified mouse O/E proteins, O/E-4 is expressed in the neuronal and basal cell layers of mouse olfactory epithelium. However, unlike other O/E members, O/E-4 expression is absent in the vomeronasal organ. O/E-4 can partner with the other O/Es to form heterodimers that are capable of binding an Olf-1 consensus site in vitro. In contrast to other O/E family members, the O/E-4 protein only weakly activates transcription in a reporter assay. In summary, we have identified O/E-4 utilizing a novel homology screening method. Our results suggest that O/E-4 may interact with other O/E family members to regulate gene expression in the olfactory sensory neurons.
