The poly(C) binding proteins (PCBPs) are encoded at five dispersed loci in the mouse and human genomes. These proteins, which can be divided into two groups, hnRNPs K/J and the aCPs (aCP1-4), are linked by a common evolutionary history, a shared triple KH domain configuration, and by their poly(C) binding specificity. Given these conserved characteristics it is remarkable to find a substantial diversity in PCBP functions. The roles of these proteins in mRNA stabilization, translational activation, and translational silencing suggest a complex and diverse set of post-transcriptional control pathways. Their additional putative functions in transcriptional control and as structural components of important DNA-protein complexes further support their remarkable structural and functional versatility. Clearly the identification of additional binding targets and delineation of corresponding control mechanisms and effector pathways will establish highly informative models for further exploration.

GTF2I and GTF2IRD1 encoding the multifunctional transcription factors TFII-I and BEN are clustered at the 7q11.23 region hemizygously deleted in Williams-Beuren syndrome (WBS), a complex multisystemic neurodevelopmental disorder. Although the biochemical properties of TFII-I family transcription factors have been studied in depth, little is known about the specialized contributions of these factors in pathways required for proper embryonic development. Here, we show that homozygous loss of either Gtf2ird1 or Gtf2i function results in multiple phenotypic manifestations, including embryonic lethality; brain hemorrhage; and vasculogenic, craniofacial, and neural tube defects in mice. Further analyses suggest that embryonic lethality may be attributable to defects in yolk sac vasculogenesis and angiogenesis. Microarray data indicate that the Gtf2ird1 homozygous phenotype is mainly caused by an impairment of the genes involved in the TGF␤RII/ Alk1/Smad5 signal transduction pathway. The effect of Gtf2i inactivation on this pathway is less prominent, but downregulation of the endothelial growth factor receptor-2 gene, resulting in the deterioration of vascular signaling, most likely exacerbates the severity of the Gtf2i mutant phenotype. A subset of Gtf2ird1 and Gtf2i heterozygotes displayed microcephaly, retarded growth, and skeletal and craniofacial defects, therefore showing that haploinsufficiency of TFII-I proteins causes various developmental anomalies that are often associated with WBS.embryonic ͉ GTF2I ͉ GTF2IRD1

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Gene families normally expand by segmental genomic duplication and subsequent sequence divergence. Although copies of partially or fully processed mRNA transcripts are occasionally retrotransposed into the genome, they are usually nonfunctional ("processed pseudogenes"). The two major cytoplasmic poly(C)-binding proteins in mammalian cells, ␣CP-1 and ␣CP-2, are implicated in a spectrum of post-transcriptional controls. These proteins are highly similar in structure and are encoded by closely related mRNAs. Based on this close relationship, we were surprised to find that one of these proteins, ␣CP-2, was encoded by a multiexon gene, whereas the second gene, ␣CP-1, was identical to and colinear with its mRNA. The ␣CP-1 and ␣CP-2 genes were shown to be single copy and were mapped to separate chromosomes. The linkage groups encompassing each of the two loci were concordant between mice and humans. These data suggested that the ␣CP-1 gene was generated by retrotransposition of a fully processed ␣CP-2 mRNA and that this event occurred well before the mammalian radiation. The stringent structural conservation of ␣CP-1 and its ubiquitous tissue distribution suggested that the retrotransposed ␣CP-1 gene was rapidly recruited to a function critical to the cell and distinct from that of its ␣CP-2 progenitor.Two highly similar human proteins, ␣CP-1 and ␣CP-2 (also known as heterogeneous nuclear ribonucleoprotein E1/PCBP1 and heterogeneous nuclear ribonucleoprotein E2/PCBP2), belong to a growing family of K homology (KH) 1 domain containing RNA-binding proteins that includes Nova-1, an autoantigen in paraneoplastic opsoclonus myoclonus ataxia (1); and FMR1, which is associated with fragile X mental retardation syndrome (2). The ␣CP proteins appear to be multifunctional. Both ␣CP-1 and ␣CP-2 have been identified as components of a ribonucleoprotein complex that assembles on the 3Ј-UTR of a subset of long-lived mRNAs (3-5) and have been linked to stabilization of human ␣-globin, rat collagen, and rat tyrosine hydroxylase mRNAs (4, 6, 7). ␣CP-1 and ␣CP-2 also function as translational coactivators of poliovirus RNA via a sequencespecific interaction with stem-loop IV of the IRES and promote poliovirus RNA replication by binding to its 5Ј-terminal cloverleaf structure (8). Finally, these proteins have been implicated in translational control of the 15-lipoxygenase mRNA (9), human Papillomavirus type 16 L2 mRNA (10), and hepatitis A virus RNA (11). Thus, the ␣CP proteins appear to mediate a variety of functions relating to mRNA stability and expression.The sequences of the human (h) ␣CP-1 and h␣CP-2 mRNAs have been previously established (12, 13), as has that of a murine (m) ␣CP-2 mRNA (heterogeneous nuclear ribonucleoprotein X (14), murine CBP (15)). With the aim of better understanding the potential roles of these related and highly abundant RNA-binding proteins as well as to establish a foundation for delineation of related genetic defects, we extended these analyses by establishing the structures of murine and human ␣CP-1 mRN...

The developmental stage-specific expression of human globin proteins is characterized by a switch from the coexpression of -and ␣-globin in the embryonic yolk sac to exclusive expression of ␣-globin during fetal and adult life. Recent studies with transgenic mice demonstrate that in addition to transcriptional control elements, full developmental silencing of the human -globin gene requires elements encoded within the transcribed region. In the current work, we establish that these latter elements operate posttranscriptionally by reducing the relative stability of -globin mRNA. Using a transgenic mouse model system, we demonstrate that human -globin mRNA is unstable in adult erythroid cells relative to the highly stable human ␣-globin mRNA. A critical determinant of the difference between ␣-and -globin mRNA stability is mapped by in vivo expression studies to their respective 3 untranslated regions (3UTRs). In vitro messenger ribonucleoprotein (mRNP) assembly assays demonstrate that the ␣-and -globin 3UTRs assemble a previously described mRNP stabilitydetermining complex, the ␣-complex, with distinctly different affinities. The diminished efficiency of ␣-complex assembly on the 3UTR results from a single C3G nucleotide substitution in a crucial polypyrimidine tract contained by both the human ␣-and -globin mRNA 3UTRs. A potential pathway for accelerated -globin mRNA decay is suggested by the observation that its 3UTR encodes a shortened poly(A) tail. Based upon these data, we propose a model for -globin gene silencing in fetal and adult erythroid cells in which posttranscriptional controls play a central role by providing for accelerated clearance of -globin transcripts.

GTF2I and GTF2IRD1 encode members of the TFII-I transcription factor family and are prime candidates in the Williams syndrome, a complex neurodevelopmental disorder. Our previous expression microarray studies implicated TFII-I proteins in the regulation of a number of genes critical in various aspects of cell physiology. Here, we combined bioinformatics and microarray results to identify TFII-I downstream targets in the vertebrate genome. These results were validated by chromatin immunoprecipitation and siRNA analysis. The collected evidence revealed the complexity of TFII-Imediated processes that involve distinct regulatory networks. Altogether, these results lead to a better understanding of specific molecular events, some of which may be responsible for the Williams syndrome phenotype.GTF2I ͉ Williams-Beuren syndrome

The results suggest that transcriptional regulation of these genes by TFII-I proteins could provide a possible genotype-phenotype link in Williams-Beuren syndrome.

GTF2I and GTF2IRD1 encode a family of closely related transcription factors TFII-I and BEN critical in embryonic development. Both genes are deleted in Williams-Beuren syndrome, a complex genetic disorder associated with neurocognitive, craniofacial, dental and skeletal abnormalities. Although genome-wide promoter analysis has revealed the existence of multiple TFII-I binding sites in embryonic stem cells (ESCs), there was no correlation between TFII-I occupancy and gene expression. Surprisingly, TFII-I recognizes the promoter sequences enriched for H3K4me3/K27me3 bivalent domain, an epigenetic signature of developmentally important genes. Moreover, we discovered significant differences in the association between TFII-I and BEN with the cis-regulatory elements in ESCs and embryonic craniofacial tissues. Our data indicate that in embryonic tissues BEN, but not the highly homologous TFII-I, is primarily recruited to target gene promoters. We propose a “feed-forward model” of gene regulation to explain the specificity of promoter recognition by TFII-I factors in eukaryotic cells.