Post-transcriptional regulatory elements and spatiotemporal specification of neocortical stem cells and projection neurons.

The mature neocortex is a unique six-layered mammalian brain region. It is composed of morphologically and functionally distinct subpopulations of primary projection neurons that form complex circuits across the central nervous system. The precisely-timed generation of projection neurons from neural stem cells governs their differentiation, postmitotic specification, and signaling, and is critical for cognitive and sensorimotor ability. Developmental perturbations to the birthdate, location, and connectivity of neocortical neurons are observed in neurological and psychiatric disorders. These facts are highlighting the importance of the precise spatiotemporal development of the neocortex regulated by intricate transcriptional, but also complex post-transcriptional events. Indeed, mRNA transcripts undergo many post-transcriptional regulatory steps before the production of functional proteins, which specify neocortical neural stem cells and subpopulations of neocortical neurons. Therefore, particular attention is paid to the differential post-transcriptional regulation of key transcripts by RNA-binding proteins, including splicing, localization, stability, and translation. We also present a transcriptome screen of candidate molecules associated with post-transcriptional mRNA processing that are differentially expressed at key developmental time points across neocortical prenatal neurogenesis.

The two zinc finger-like domains of GATA-1 have different DNA binding specificities.

The GATA-1 transcription factor has been shown to be important in the regulation of globin and non-globin genes in erythroid, megakaryocytic and mast cell lineages. It is a member of a family of GATA proteins which both overlap in their expression patterns and bind the motif (A/T)GATA(A/G). The GATA family of proteins are also members of the superfamily of zinc finger-like domain proteins and have two similar domains of the type Cys-X2-Cys-X17-Cys-X2-Cys which direct the DNA binding of the protein. A random oligonucleotide selection procedure has been employed to further elucidate the mechanism of GATA-1-DNA recognition. The resulting oligonucleotides were tested for binding activity to both wild-type and mutant GATA-1 proteins. Two classes of GATA-1-DNA interaction have been defined, the first requiring only the carboxy finger of GATA-1 to bind and having the motif GAT(A/T), the second requiring both finger domains to bind and having the core motif (T/C)AAG. By using sequence comparison and depurination analysis it is concluded that the two finger-like domains of GATA-1 have different DNA binding recognition motifs. Binding of GATA-1 to GAT(A/T) motifs is associated with transcriptional activation of linked genes. The only known (T/C)AAG motif is in the distal CAAT-box promoter region of the human A gamma-globin gene where the binding of GATA-1 appears to regulate the correct developmental suppression of gamma-globin expression.

Contamination of dairy products by fungal metabolites.

The contamination of dairy products with various mycotoxins or other undesirable fungal metabolites can be attributed a.o. to ingestion of contaminated feed or the accidental development of molds and by consequence the excretion of fungal metabolites into the intermediate product. Different dairy products of commercial origin were examined: milk powder, reconstituted infant milk powder, and cheese. In addition to that, environmental factors contributing to the formation of the undesired fungal metabolites were studied. It was found that the presence of mycotoxins in dairy products is more related to the environmental factors causing mold growth on dairy products than to the ingestion of moldy feed by the cow.

Nuclear protein factors and erythroid transcription of the human A gamma-globin gene.

We have used DNaseI footprinting and gel mobility assays to analyze the upstream region of the human A gamma-globin gene promoter. Four protein factors were found to bind this region. A non-erythroid factor present in the 0.4M KCl fraction of a heparin agarose column binds to the CAC box (-140). A ubiquitous octamer factor present in the 0.2M fraction binds to an ATGCAAT element (-175), but is completed out by the erythroid specific factor NF-E1 (in the 0.4M KCl fraction), which binds a site (-186) immediately flanking the octamer. A novel factor binding to a stretch of 8A around -233, was identified in the 0.2M KCl fraction. This factor is not present in HeLa nuclear extracts. To study the transcriptional importance of these protein binding sites we have used an "A gamma-minilocus", similar to that described for the beta-globin gene (1) in K562 cells. This provides evidence that the NF-E1 and CAC box in the -210 to -122 region of the A gamma-promoter are important for the efficient expression of the gamma-globin gene.

Two tissue-specific factors bind the erythroid promoter of the human porphobilinogen deaminase gene.

We have studied the erythroid-specific promoter of the human gene coding for Porphobilinogen Deaminase (PBGD) by DNaseI footprinting, gel retardation and methylation interference assays. We show that this promoter, which is inducible during MEL cell differentiation, contains three binding sites for the erythroid-specific factor NF-E1 and one site for a second erythroid-specific factor, which we name NF-E2. NF-E1 is a factor that also binds the promoter and the enhancer (present in the 3' flanking region) of the human beta-globin gene. NF-E2 has not yet been described and although it binds to a sequence containing the Ap1 consensus, it appears to be different from Ap1.

The human beta-globin promoter; nuclear protein factors and erythroid specific induction of transcription.

We have shown that the promoter of the human beta-globin gene contains three regions in addition to the known CAC, CAAT and TATA box regions that are important for the induction of transcription in erythroid cells. By using DNaseI footprinting and gel mobility shift assays we were able to show that two of these regions bind the erythroid specific nuclear factor NF-E1 (and ubiquitous factors). The third region binds a ubiquitous CAAT-box factor (CP1). Deletion experiments suggest that only the combination of NF-E1 and CP1 binding sites, but not each of the sites alone, are capable of mediating the induction of transcription of a minimal (CAC, CAAT, TATA box) beta-globin promoter in mouse erythroleukaemia (MEL) cells.

The human beta-globin gene 3' enhancer contains multiple binding sites for an erythroid-specific protein.

We have shown that the minimal enhancer fragment present in the 3'-flanking region of the human beta-globin gene contains four regions that bind nuclear proteins in vitro. By using gel mobility shift and DNase I footprinting assays, we were able to show that each of these regions binds an erythroid-cell-specific nuclear factor which we name NF-E1. This factor is present in erythroid cells at different developmental stages of globin gene expression. The recognition sequence of this protein (A/C Py T/A ATC A/T Py) is also present in the intragenic enhancer and the promoter of the beta-globin gene as well as in the promoter of other erythroid-cell specific genes. In addition to NF-E1, each of the four binding regions interacts with at least one other protein factor.

The human beta-globin gene contains multiple regulatory regions: identification of one promoter and two downstream enhancers.

We have introduced into murine erythroleukaemia (MEL) cells several series of deletion mutants of hybrid genes between the human beta-globin gene and the murine H-2Kb gene. S1 nuclease and transcriptional run-off analysis showed that the human beta-globin gene contains at least three globin specific transcriptional control elements. One is a promoter element and is located 160 bp upstream from the transcription initiation site; it increases the efficiency of the promoter after MEL cells are induced to differentiate. The other two elements are tissue-specific transcriptional enhancers and are located downstream from the transcription initiation site, the first in the structural beta-globin gene and the second in the 3' flanking sequences.

The human beta-globin gene contains a downstream developmental specific enhancer.

The human beta-globin gene is part of a multigene family and is expressed specifically in adult human erythroid tissue (for review, 1). When the human beta-globin is introduced into fertilized mouse eggs, it is first activated in foetal liver and remains expressed in adult erythroid tissues. It therefore mimicks the pattern of expression of its murine counterpart. It has previously been shown in tissue culture and transgenic mice that sequences downstream from the beta-globin promoter are involved in this regulation. We now show that at least part of these sequences are located 0.5-1.2kb downstream from the poly A addition site and constitute a transcriptional enhancer element that is erythroid and developmental specific.

Beta-globin gene promoter generates 5' truncated transcripts in the embryonic/fetal erythroid environment.

We report here the localisation of sequences responsible for the faulty expression of human beta-globin gene in Putko and K562 cells. Complete beta-globin gene introduced into these cells produces transcripts with abnormal 5' ends, while cotransfected mouse H2 gene is expressed correctly. Using hybrid constructs of these two genes we demonstrate that aberrant activity is conferred by sequences 5' of the beta-globin gene. Thus beta-globin promoter attached to the H2 coding sequence produces H2 transcripts with truncated 5' ends. By introducing a series of deletions in the beta-globin promoter we restrict these sequences to the -77/+28 base pair region spanning the CAAT element to the translation initiation site. These results are consistent with the lack of recognition of the beta-globin gene major cap site in Putko and K562 cells. We suggest that inactivity of the adult globin gene in the embryonic/fetal environment is at least in part conferred by sequences within the beta-globin gene promoter.

DNA sequences required for regulated expression of beta-globin genes in murine erythroleukaemia cells.

We have introduced into murine erythroleukaemia (MEL) cells a series of human globin gene cosmids and two sets of hybrid genes constructed from the human beta-globin gene and the human gamma-globin or murine H-2Kbm1 genes. S1-nuclease analysis of the mRNA products from these genes before and after MEL cell differentiation showed that the human beta-globin gene, but not the human epsilon- or gamma-globin or H-2Kbm1 genes, is induced specifically. Hybrid genes containing human beta-globin DNA sequences from either 5' or 3' side of the translation initiation site were both inducible. Measurement of the relative rate of transcription showed this induction to be the result of transcriptional activation. We therefore suggest that DNA sequences which regulate beta-globin gene expression during MEL differentiation are located both 5' and 3' to the translation initiation site.

Regulated expression of the human beta-globin gene family in murine erythroleukaemia cells.

Chemically induced differentiation of cultured murine erythroleukaemia (MEL) cells results in a several hundred-fold increase in transcription of the adult mouse globin genes and thus serves as a model for gene activation during erythropoiesis. One approach to study gene regulation in this system has been to analyse the expression of foreign globin genes introduced into MEL cells. By introducing cosmid DNA containing the human adult(beta), fetal(gamma) and embryonic(epsilon)-globin genes, we have shown here that expression of the beta, but not the gamma or epsilon genes, is regulated during MEL differentiation. Regulated expression of the human beta-globin gene was observed when it was introduced either as part of the intact globin gene cluster or as an individual gene with 1.5 kilobases (kb) of 5' flanking DNA. Transcription from a herpes simplex virus (HSV) promoter adjacent to the thymidine kinase (tk) gene is also inducible in MEL cells.

The sequence GGCmCGG is resistant to MspI cleavage.

MspI essentially fails to cut the sequence GGCmCGG at enzyme concentrations which give total digestion of CCGG, CmCGG and GGCCGG sites. This result explains why certain sites in mammalian DNA are resistant to both MspI and HpaII and shows that this results from an idiosynchracy of MspI rather than a novel form of DNA methylation at this site in mammalian cells.