The genomic organization of the human EBF-1 and Drosophila Collier is partially conserved, as shown in this comparison between the exon structure of Drosophila (dCOE) and human (hCOE1) genes. Only the coding parts of the genes are shown. Exons are indicated with numbers, and splice junctions are indicated with lines. The dotted line represents an alternative splice site for joining the human exon 6 to exon 7, creating the 0 form of hCOE1.

EBF/O/E-1 is a central transcriptional regulator in the developing B lymphocyte. The figure displays the suggested functional relationships between the transcription factors E2A, O/E-1, and Pax-5. Suggested target genes are located under the transcription factors and common target genes are indicated by arrows. The flow and stage of B-cell development are indicated in the right part of the figure by a broad shaded arrow.

O/E proteins participate in the transcription factor network involved in adipocyte differentiation. (A) Schematic illustration of adipocyte differentiation in which the cells go through several distinct steps of development before becoming mature adipocytes. Temporal expressions of transcription factors important for adipogenesis, including O/E-1, are indicated. (B) Model of the hierarchy of transcription factors controlling adipogenesis, with possible roles of O/E-1 in this network indicated.

Phylogenetic tree of the COE family, revealing the genetic relations between the different COE proteins. Sequences were retrieved from the EBI database, and the tree was constructed using the ClustalW method (61). The proteins are referred to in the figure with the prefixes h (human), m (mouse), r (rat), z (zebra fish), g (chicken), s (skate), d (Drosophila), x (Xenopus), or c (C. elegans).

COE proteins contain several domains highly conserved in evolution. (A) Schematic structure of mouse COE1. The DBD is colored green and the amino acids and suggested structure of the Zn coordination motif are indicated. The IPT/TIG domain is indicated in orange, putative helix 1 is shown in red, and helix 2 motifs are shown in blue. The carboxy-terminal transactivation domain is colored yellow. (B) Comparison between COE proteins of different species. The color codes are the same as in panel A. All mouse (mCOE), human (hCOE), and Xenopus (xCOE) proteins are homologous throughout the protein. Two sites of variation are indicated where alternative splicing leads to different forms of COE1 and COE3. The (0) forms of murine COE1 and COE3 lack an 8- or 9-amino-acid region (indicated by variation I), which is present in COE1 (8) and COE3 (9). The S form of COE3 lacks the region indicated by variation II, which is present in COE3 L. Mouse COE4 has a more complex splicing pattern and, as COE1 (0) and COE3 (0), lacks the region indicated as variation I. Zebra fish COE (zCOE) is homologous to the other vertebrate proteins in all parts except for an unrelated sequence between the DBD and IPT/TIG domains (shaded in darker grey). Drosophila COE (dCOE) exists in two isoforms of 575 (isoform 1) or 557 (isoform 2) amino acids. They are identical until amino acid 528 (indicated in figure) but differ in their C-terminal sequence.