Molecular cloning and characterization of a novel mouse macrophage gene that encodes a nuclear protein comprising polyglutamine repeats and interspersing histidines

Temperature entrainment of Drosophila's circadian clock involves the gene nocte and signaling from peripheral sensory tissues to the brain

Circadian clocks are synchronized by the natural day/night and temperature cycles. Our previous work demonstrated that synchronization by temperature is a tissue autonomous process, similar to synchronization by light. We show here that this is indeed the case, with the important exception of the brain. Using luciferase imaging we demonstrate that brain clock neurons depend on signals from peripheral tissues in order to be synchronized by temperature. Reducing the function of the gene nocte in chordotonal organs changes their structure and function and dramatically interferes with temperature synchronization of behavioral activity. Other mutants known to affect the function of these sensory organs also interfere with temperature synchronization, demonstrating the importance of nocte in this process and identifying the chordotonal organs as relevant sensory structures. Our work reveals surprising and important mechanistic differences between light- and temperature-synchronization and advances our understanding of how clock resetting is accomplished in nature.

Analysis of cag-8: A novel poly(Q)-encoding gene in the mouse brain

We identified 13 transcript isoforms of a trinucleotide-repeat-containing gene, cag-8, that is expressed almost exclusively in the mouse brain. The polypeptide deduced from the cDNA consists of 137 AAs, of which 74 are glutamines. The 130-kb gene is composed of 16 exons, from which at least 13 isoforms with variable UTRs are formed by alternative splicing. A strong positive cis-acting element was found in the neuroblastomaxglioma hybrid NG108-15 and human embryonic kidney HEK293 cell lines. The cag-8 protein was localized in the cytosol and in granular bodies within the nucleus. These findings indicate that cag-8 is a novel poly(Q)-encoding gene, the expression of which is confined primarily to the brain.

Impaired maturation of myeloid progenitors in mice lacking novel Polycomb group protein MBT-1

Polycomb group (PcG) proteins participate in DNA-binding complexes with gene-repressing activity, many of which have been highlighted for their involvement in hematopoiesis. We have identified a putative PcG protein, termed MBT-1, that is associated with Rnf2, an in vivo interactor of PcG proteins. MBT-1 structurally resembles the H-L(3)MBT protein, whose deletion is predicted to be responsible for myeloid hematopoietic malignancies. The human MBT-1 gene is located on chromosome 6q23, a region frequently deleted in leukemia cells, and shows a transient expression spike in response to maturation-inducing stimuli in myeloid leukemia cells. MBT-1(-/-) myeloid progenitor cells exhibit a maturational deficiency but maintain normal proliferative activities. This results in the accumulation of immature myeloid progenitors and hence, a marked decrease of mature myeloid blood cells, causing the MBT-1(-/-) mice to die of anemia during a late embryonic stage. Together, we conclude that MBT-1 specifically regulates the maturational advancement of myeloid progenitor cells during transitions between two developmental stages. We also show that MBT-1 appears to influence myelopoiesis by transiently enhancing p57(KIP2) expression levels.

Colletotrichum trifolii TB3 kinase, a COT1 homolog, is light inducible and becomes localized in the nucleus during hyphal elongation

Colletotrichum trifolii is a fungal pathogen responsible for anthracnose disease of alfalfa. Previously, a serine/threonine protein kinase gene from this fungus (TB3), which is a functional homolog of the Neurospora crassa COT1 kinase, has been isolated in our laboratory and appears to be associated with hyphal elongation and branching. In this report we show that light treatment rapidly induces TB3 expression and hyphal branching frequency. Western analysis showed TB3 localization in both the cytoplasm and nucleus, but not in membranes. Moreover, indirect immunofluorescence indicated that TB3 levels were most abundant in the nucleus. To further evaluate the subcellular distribution of TB3, a TB3::GFP fusion construct was inserted into C. trifolii. Results indicated that the cellular location of TB3 changed during fungal growth and development. Consistent with previous observations, TB3 was localized in both the cytoplasm and the nucleus but was preferentially localized in the nucleus during extended hyphal growth. The amino terminus of TB3 contains two relatively long polyglutamine repeats. Yeast-based assays showed that these polyglutamine tracts can activate transcription. These results suggest that TB3 may be positioned in a signaling cascade regulating proper hyphal growth and development by functioning as a transcription factor.

A novel glutamine-rich putative transcriptional adaptor protein (TIG-1), preferentially expressed in placental and bone-marrow tissues

We used a subtractive hybridization protocol to identify novel expressed sequence tags (ESTs) corresponding to mRNAs whose expression was induced upon exposure of the human leukemia cell line K562 to the phorbol ester 12-O-tetradecanolyphorbol-13-acetate (TPA). The complete open reading frame of one of the novel ESTs, named TIG-1, was obtained by screening K562 cell and placental cDNA libraries. The deduced open reading frame of the TIG-1 cDNA encodes for a glutamine repeat-rich protein with a predicted molecular weight of 63kDa. The predicted open reading frame also contains a consensus bipartite nuclear localization signal, though no specific DNA-binding domain is found. The corresponding TIG-1 mRNA is ubiquitously expressed. Placental tissue expresses the TIG-1 mRNA 200 times more than the lowest expressing tissues such as kidney and lung. There is also preferential TIG-1 mRNA expression in cells of bone-marrow lineage.In-vitro transcription/translation of the TIG-1 cDNA yielded a polypeptide with an apparent molecular weight of 97kDa. Using polyclonal antibodies obtained from a rabbit immunized with the carboxy-terminal portion of bacterially expressed TIG-1 protein, a polypeptide with molecular weight of 97kDa was identified by Western blot analyses of protein lysates obtained from K562 cells. Cotransfection assays of K562 cells, using a GAL4-TIG-1 fusion gene and GAL4 operator-CAT, indicate that the TIG-1 protein may have transcriptional regulatory activity when tethered to DNA. We hypothesize that this novel glutamine-rich protein participates in a protein complex that regulates gene transcription. It has been demonstrated by Naar et al. (Naar, A.M., Beaurang, P.A., Zhou, S., Abraham, S., Solomon, W.B., Tjian, R., 1999, Composite co-activator ARC mediates chromatin-directed transcriptional activation. Nature 398, 828-830) that the amino acid sequences of peptide fragments obtained from a polypeptide found in a complex of proteins that alters chromatin structure (ARC) are identical to portions of the deduced open reading frame of TIG-1 mRNA.

Simple sequence is abundant in eukaryotic proteins

All proteins of Saccharomyces cerevisiae have been compared to determine how frequently segments from one protein are present in other proteins. Proteins that are recently evolutionarily related were excluded. The most frequently present protein segments are long, tandem repetitions of a single amino acid. For some of these segments, up to 14% of all proteins in the genome were found to have similar peptides within them. These peptide segments may not be functional protein domains. Although they are the most common shared feature of yeast proteins, their ubiquity and simplicity argue that their probable function may be to simply serve as spacers between other protein motifs.

Structural features of single amino acid repeats in proteins

Single amino acid repeats are found in different kinds of proteins. Some of these repeats are pathogenic. It is striking that some amino acids are able to form such repeats, but other amino acids are not. We suggest an explanation for this fact based on the different tendency of each amino acid to form aggregates. Aggregation may be due to the formation of incipient lamellar crystals as they have been described in poly-alpha-amino acids and in most synthetic polymers.

Testes exhibit elevated expression of calcitonin gene-related peptide receptor component protein

Calcitonin gene-related peptide (CGRP) receptor component protein (RCP) is a novel protein that modulates CGRP responsiveness in a variety of cell types. Using probes based on the isolation of CGRP-RCP complementary DNA (cDNA) from a guinea pig organ of Corti cDNA library, we cloned human (h) and mouse (m) CGRP-RCP cDNAs, both of which encode 148-residue proteins that at the amino acid levels are approximately 88% identical to each other and to the 146-residue guinea pig CGRP-RCP. Northern blot analysis confirmed the presence of CGRP-RCP messenger RNA in all of the human and mouse tissues tested. In these human tissues, hCGRP-RCP messenger RNA (major band at approximately 3.1 kb, minor band at approximately 7.5 kb) was most prevalent in the testis. In the mouse, the highest abundance of CGRP-RCP RNA was clearly in the testis (major band at approximately 1.6 kb, minor band at approximately 1.1 kb). Based on this tissue distribution of RNA, we sought to identify the cells in the murine testis that contained CGRP-RCP protein. Numerous antisera generated against hCGRP-RCP, including one to recombinant hCGRP-RCP, exhibited strong immunoreactivity localized to the head region of spermatozoa. No CGRP-RCP immunoreactivity was observed in other cells at less mature stages of sperm maturation, in Sertoli or interstitial (Leydig) cells, or in human spermatozoa. Murine epididymal (mature) spermatozoa exhibited CGRP-RCP immunoreactivity identical to that of testicular spermatozoa. Spermatozoa that underwent an experimentally induced acrosome reaction (acrosomal discharge) lost their CGRP-RCP immunoreactivity. Therefore, it appears that CGRP-RCP is associated with the acrosome, suggesting that it may play an important role in reproduction.