Structural analysis of the gene for the beta chain of the antigen-specific receptor of mammalian T-lymphocytes

The antigen specific receptor of T cells (TCR) is composed of alpha and beta chains and is normally present on the T cell surface complexed with the components which make up T3. In the case of beta chain, multiple somatic DNA rearrangements bring together V beta (variable), D beta (diversity) and J beta (joining) gene segments before a mature messenger RNA can be transcribed. So far beta chain genes have been extensively studied in the human and in the mouse system and we have very little information on other mammals. Our aims were to obtain information that may provide a structural basis for understanding developmental as well as evolutionary aspects of the TCR gene system in mammals. In this study we compare the hybridization pattern between a human cDNA probe coding for the beta chain constant region and restricted genomic DNA extracted from lymphocytes deriving from human as well as from rat and lamb. The comparison of the hybridization data represent a first piece of information about the variation of the structure of the TCR beta chain genes in mammals.     

The lack of protamine 2 (P2) in boar and bull spermatozoa is due to mutations within the P2 gene.

The nuclei of spermatozoa in all mammals examined so far contain P1 protamine. A second protamine variant, protamine P2, has to date been isolated only from human and murine spermatozoa where it represents the major fraction of basic nuclear protein. In order to elucidate the reason for this unusual distribution of the protamine variants among mammals we have investigated the expression of protamine P2 in boar and bull. It can be shown that also in these species protamine 2 is transcribed and translated on low levels. Various mutational events though have altered the primary structure of the protein: In boar, a deletion of 8 aminoacids has removed a sequence motif from the amino-terminus of the molecule, which highly probable is of functional relevance. The bovine sequence, as a consequence of numerous point mutations has accumulated neutral and hydrophobic aminoacids which reduce the affinity of the protamine 2 to DNA.     

Structure of the 5'-external transcribed spacer of the human ribosomal RNA gene

We report the complete nucleotide sequence of the 3627 bp long 5'-external transcribed spacer (ETS) of a human ribosomal RNA gene. This sequence exhibits only very limited homologies with its mouse counterpart, the only other mammalian specimen analyzed so far. It has very peculiar compositional characteristics, with a highly biased base content (very rich in G + C, very poor in A) and also some very strong dinucleotide preferences. Interestingly, these specific features are shared by the mouse sequence, despite the extensive sequence divergence, and also apply to the other transcribed spacers of mammals indicating that a common and strong structural constraint is exerted on all these regions of the ribosomal gene. An outstanding secondary structure can be formed within the human ETS RNA, which could have a significant role in preribosome assembly.     

Structure and expression of the zebrafish mest gene, an ortholog of mammalian imprinted gene PEG1/MEST

PEG1/MEST is a paternally expressed gene in placental mammals. Here, we report identification of zebrafish (Danio rerio) gene mest, an ortholog of mammalian PEG1/MEST. Zebrafish mest encodes a polypeptide of 344 amino acids and shows a significant similarity to mammalian orthologs. Zebrafish mest is present as a single copy in the zebrafish genome and is closely linked to copg2 as in mammals. It is notable that 10 of 11 intron positions in mest are conserved among mammalian PEG1/MEST genes, indicating that the genomic organization and linkage between mest and copg2 loci was established in ancient vertebrates. Zebrafish mest is expressed in blastula, segmentation, and larval stages, exhibiting gradually increased expression as the development proceeds. Allelic expression analysis in hybrid larvae shows that both parental alleles are transcribed. We also observed one-codon alternative splicing involving an alternative usage of the two consecutive splice acceptors of intron 1, generating two protein isoforms with different lengths of a single amino acid.     

Roles of long, non-coding RNA in chromosome-wide transcription regulation: lessons from two dosage compensation systems

A large part of higher eukaryotic genomes is transcribed into RNAs lacking any significant open reading frame. This "non-coding part" has been shown to actively contribute to regulating gene expression, but the mechanisms are largely unknown. Particularly instructive examples are provided by the dosage compensation systems, which assure that the single X chromosome in male cells and the two X chromosomes in female cells give rise to similar amounts of gene product. Although this is achieved by very different strategies in mammals and fruit flies, long, non-coding RNAs (lncRNAs) are involved in both cases. Here we summarize recent progress towards unraveling the mechanisms, by which the Xist and roX RNAs mediate the selective association of regulators with individual target chromosomes, to initiate dosage compensation in mammals and fruit flies, respectively.     

A novel form of oxytocin in New World monkeys

Oxytocin is widely believed to be present and structurally identical in all placental mammals. Here, we report that multiple species of New World monkeys possess a novel form of oxytocin, [P8] oxytocin. This mutation arises from a substitution of a leucine to a proline in amino acid position 8. Further analysis of this mutation in Saimiri sciureus (squirrel monkey) indicates that [P8] oxytocin is transcribed and translated properly. This mutation is specific to oxytocin, as the peptide sequence for arginine vasopressin, a structurally related nonapeptide, is unaltered. These findings dispel the notion that all placental mammals possess a 'universal' oxytocin sequence, and highlight the need for research on the functional significance of this novel nonapeptide in New World monkeys.