The Characterization of the Olf-1/EBF-Like HLH Transcription Factor Family: Implications in Olfactory Gene Regulation and Neuronal Development

Abstract

The Olf-1/EBF helix-loop-helix (HLH) transcription factor has been implicated in olfactory gene regulation and in B-cell development. Using homology screening methods, we identified two additional Olf-1/EBF-like cDNAs from a mouse embryonic cDNA library. The Olf-1/EBF-like (O/E) proteins O/E-1, O/E-2, and O/E-3 define a family of transcription factors that share structural similarities and biochemical activities. Although these O/E genes are expressed within olfactory epithelium in an identical pattern, they exhibit different patterns of expression in the developing nervous system. Although O/E-1 mRNA is present in several tissues in addition to olfactory neurons and developing B-cells, O/E-2 and O/E-3 are expressed at high levels only in olfactory tissue. In O/E-1 knock-out animals, the presence of two additional O/E family members in olfactory neurons may provide redundancy and allow normal olfactory neurodevelopment. Further, the identification of the O/E family of HLH transcription factors and their embryonic expression patterns suggest that the O/E proteins may have a more general function in neuronal development.

Cloning and Functional Characterization of Roaz, a Zinc Finger Protein that Interacts with O/E-1 to Regulate Gene Expression: Implications for Olfactory Neuronal Development

“…The GST protein was isolated in a similar way. Whole-cell extracts for binding studies were isolated as described above from HEK293 cells transfected with pCIS-O/E-1, O/E-2, or O/E-3 plasmid (Wang et al, 1997). The extracts (400 g) were mixed with 6 -8 g of GST-RoazD86 fusion protein bound to 30 l of glutathione-agarose beads and rocked for 2 hr at 4°C.…”

“…We recently have identified a family of O/ E-1-like proteins (the O/ E proteins), displaying redundant biochemical and functional activities, which are expressed in olfactory epithelium, but not in tissues in which B-cell progenitors reside. These observations could account for the lack of an obvious phenotype in the olfactory epithelium for the O/ E-1 knockout mice (Wang et al, 1997).…”

“…The importance of these sites has been demonstrated in transgenic mice, in which 300 bp containing the O/ E site in OMP promoter is sufficient to drive olfactory neuron-specific reporter expression, and mutation of that site disrupts the olfactory-specific pattern (Walters et al, 1996). The existence of a family of related O/ E proteins expressed in the olfactory epithelium that display a high degree of functional redundancy (Wang et al, 1997) is consistent with an important role for these factors in olfactory neuronal gene expression and explains the lack of an observable phenotype when expression of one member is abolished by gene disruption . Although we have described in this paper the interactions between Roaz and the canonical member of the O/ E protein family O/ E-1, the existence of similar interactions with the other members of the O/ E family expressed in the olfactory epithelium is consistent with the importance of Roaz in the pathway of O/ E-regulated gene expression.…”

Xath5 regulates neurogenesis in the Xenopus olfactory placode

“…In Drosophila, these genes are required for sensory neuron development (Campos-Ortega, 1997). The rHLH protein Olfactory neuronal transcription factor (Olf-1) was identified in rat for its role in regulating olfactory gene expression (Wang et al, 1997). Additional rHLH homologues to Olf-1, the Early B cell factor genes, were identified in mouse (Ebf, Ebf 2, Ebf 3) as well as in Xenopus (Xebf2, Xebf3), Zebrafish (Zcoe2), and Caenorhabditis elegans (unc 3/CeO/E; Garel et al, 1997;Dubois et al, 1998;Bally-Cuif et al, 1998;Prasad et al, 1998;Pozzoli et al, 2001).…”

“…These proteins have been shown in vitro to bind the promoters and activate the expression of several olfactory neuron-specific genes, such as olfactory specific adenylyl cyclase III (Ac-III), olfactory marker protein (OMP), and the olfactory cy-clic nucleotide gated channel (OcNC) (Wang et al, , 1997. These data argue that the Ebf proteins may directly regulate the genes specific to odorant detection and/or the commitment of olfactory precursor cells to the ORN lineage.…”