Embryonic Lethality, Decreased Erythropoiesis, and Defective Octamer-Dependent Promoter Activation in Oct-1-Deficient Mice

Abstract

Oct-1 is a sequence-specific DNA binding transcription factor that is believed to regulate a large group of tissue-specific and ubiquitous genes. Both Oct-1 and the related but tissue-restricted Oct-2 protein bind to a DNA sequence termed the octamer motif (5-ATGCAAAT-3) with equal affinity in vitro. To address the role of Oct-1 in vivo, an Oct-1-deficient mouse strain was generated by gene targeting. Oct-1-deficient embryos died during gestation, frequently appeared anemic, and suffered from a lack of Ter-119-positive erythroid precursor cells. This defect was cell intrinsic. Fibroblasts derived from these embryos displayed a dramatic decrease in Oct-1 DNA binding activity and a lack of octamer-dependent promoter activity in transient transfection assays. Interestingly, several endogenous genes thought to be regulated by Oct-1 showed no change in expression. When crossed to Oct-2 ؉/؊ animals, transheterozygotes were recovered at a very low frequency. These findings suggest a critical role for Oct-1 during development and a stringent gene dosage effect with Oct-2 in mediating postnatal survival.Gene expression is mediated by the interaction of transacting factors with cis-acting elements in promoters and enhancers. The octamer-binding proteins Oct-1 and Oct-2 control gene expression by interacting with the octamer element 5Ј-ATGCAAAT-3Ј and related motifs (6,50,54,55,57). Their DNA binding domains are highly homologous, and both proteins bind DNA with equal affinity in vitro (29). Expression studies indicate that Oct-1 is ubiquitously expressed, whereas Oct-2 is restricted to B cells, macrophages, and other hematopoietic cells, as well as cells of the central nervous system.Oct-1 and Oct-2 belong to the POU domain family of transcription factors, which was identified after the isolation of three mammalian transcription factors and a Caenorhabditis elegans developmental regulator: Pit-1, Oct-1, Oct-2 and unc-86 (16). The POU domain consists of a bipartite DNAbinding motif, the POU-specific and POU homeodomain, tethered by a linker domain of approximately 20 amino acids (60, 66). X-ray crystallography studies reveal that the POU subdomains of Oct-1 both contact the major groove but on opposite sides of the DNA (26), with the POU-specific domain contacting the 5Ј-ATGC subsite and the POU homeodomain binding the AAAT-3Ј subsite. Such cooperative binding between adjacent subdomains resulting in the recognition of asymmetrical DNA motifs is characteristic of POU domain transcription factors.With the exception of the ubiquitously expressed Oct-1, all of the known mouse POU domain factors are expressed in restricted temporal and spatial patterns during development (reviewed in reference 49). Gene targeting experiments have provided direct evidence that the POU domain proteins play a critical role in the determination of cell fates. For example, deficiency of the POU domain protein Pit-1 results in pituitary hypoplasia and dwarfism (33,44). Mutation of Brn-3

Oct1 and OCA-B are selectively required for CD4 memory T cell function

“…6 B). WT splenic WT (Continued) deficiency, the slightly less robust phenotype is likely attributable to the hypomorphic Oct1 allele (Wang et al, 2004), the presence of low amounts of Oct2 in CD4 + T cells, or incomplete deletion (see Fig. 7 G below).…”

Herpes simplex virus infections are arrested in Oct-1-deficient cells

“…Recently a genetic model of Oct-1 deficiency has been described in which the third exon of Oct-1 was replaced by a neomycin resistance cassette in the antisense transcriptional orientation (29). Mice harboring this severely hypomorphic allele of Oct-1 die in utero between embryonic day 13.5 and embryonic day 18.5 and display erythropoietic defects.…”

DNA-PK phosphorylation sites on Oct-1 promote cell survival following DNA damage

“…Substitution of DNA-PK phosphorylation sites in the Oct-1 N-terminus prevents upregulation and phosphorylation in response to IR To investigate the importance of the residues targeted by DNA-PK in vitro for the stabilization of Oct-1 in mammalian cells in response to IR treatment, we expressed HA-tagged Oct-1-bearing S/T-A substitutions across the N-terminal A, B and C regions (mtABC) in Oct-1-deficient 3T3-immortalized MEFs (Wang et al, 2004). As described previously , WT HA-Oct-1 expressed by transient transfection in the MEFs was stabilized about two fold following IR exposure (Figure 3a).…”

“…Ku70 þ / þ and Ku70-deficient (Ku70 À/À ) MEFs were cultured as described (Sawada et al, 2003). 3T3-immortalized MEFs derived from WT and Oct-1-deficient mice have been described previously (Wang et al, 2004). For irradiation experiments, cells were plated the night before irradiation at 50-70% confluency.…”

“…Oct-1 also participates in the transcriptional regulation of many signal-regulated and tissuespecific genes and in the control of viral replication (Herr and Cleary, 1995;Ryan and Rosenfeld, 1997;de Jong and van der Vliet, 1999;Phillips and Luisi, 2000). Oct-1 is essential for embryonic development as Oct-1-deficient embryos die during gestation (Wang et al, 2004).…”