Molecular evolution of the mouse proline-rich protein multigene family. Insertion of a long interspersed repeated DNA element

Codominant expression of genes coding for different sets of inducible salivary polypeptides associated with parotid hypertrophy in two inbred mouse strains

Experimental mouse parotid hypertrophy has been associated with the expression of a number of isoproterenol-induced salivary proline-rich polypeptides (IISPs). Mouse salivary proline-rich proteins (PRPs) have been mapped both to chromosomes 6 and 8. Recently, mice of two inbred strains (A/Snell and A. Swiss) have been found to differ drastically in the IISPs. In this study, mice of both strains were used for cross-breeding experiments addressed to define the pattern of inheritance of the IISP phenotype and to establish whether the IISPs are coded on a single or on several chromosomes. The IISP phenotype of individual mice was assessed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) of whole saliva collected after three daily stimulations by isoproterenol. Parental A/Snell and A. Swiss mice were homogeneous for distinctive strain-associated IISP-patterns. First filial generation (F1) mice obtained from the cross of A/Snell with A. Swiss mice expressed with no exception both the A/Snell and A. Swiss IISPs (coexpression). In the second filial generation (F2) both parental IISP phenotypes reappeared together with a majority of mice expressing the F1-hybrid phenotype (1:2:1 ratio). Backcrosses of F1 x A/Snell and F1 x A. Swiss produced offsprings displaying the F1 and the corresponding parental phenotypes with a 1:1 ratio. No recombinants were observed among F2 mice or among mice resulting from backcrosses. Thus, genes coding for the IISPs that are expressed differentially in both mouse strains are located on the same chromosome, probably at the same locus (alleles) or at quite closely linked loci (nonalleles).

cDNA cloning, genomic structure, chromosomal mapping, and expression analysis of parotid secretory protein in pig

A novel cDNA has been isolated from pig parotid glands by 3' and 5' rapid amplification of cDNA ends and designated parotid secretory protein (PSP). The open reading frame of this cDNA covers 714 bases, encoding 238 amino acids, which show 56% identity with human PSP at the level of the primary protein structure. The PSP genomic sequence comprises eight exons and seven introns, is approximately 22 kb in size, determined by sequencing, and maps to pig chromosome 17q21-q23. RT-PCR, dot blot, and Northern blot analyses demonstrated that PSP is strongly expressed in parotid glands, but is not present in heart, liver, lung, kidney, muscle, or stomach. A search for functionally significant protein motifs revealed consensus sequences for casein kinase II phosphorylation and N-myristoylation. We observed a unique amino acid sequence pattern consisting of the residues Leu-X(6)-Leu-X(6)-Leu-X(7)-Leu-X(6)-Leu-X(6)-Leu near the amino-terminal portion of the protein, which is similar to the leucine zipper.

Differential expression of isoproterenol-induced salivary polypeptides in two mouse strains that are congenic for the H-2 histocompatibility gene complex

Two inbred mouse strains, A/Snell and A.Swiss, which were produced as congenic with regard to the H-2 histocompatibility gene complex, are homozygous for two different groups of isoproterenol-induced salivary polypeptides (IISP). These polypeptides, which have been considered as markers of the hypertrophic growth of the parotid acinar cells, are members of the complex family of salivary proline-rich proteins (PRP) on the basis of both their massive accumulation in the parotid acinar cells in response to chronic isoproterenol, secretory character, high solubility in trichloroacetic acid and metachromatic staining by Coomassie blue. IISP expressed in both mouse strains were identified by unidimensional SDS-polyacrylamide electrophoresis and Coomassie blue staining both in parotid gland homogenates and in whole salivas obtained from mice repeatedly stimulated at 24-h intervals with isoproterenol. Parotid glands from 40 mice (20 A/Snell and 20 A.Swiss) and salivas from 270 mice (200 A/Snell and 70 A.Swiss) were analyzed. One of the congenic strains (A/Snell) expressed five IISP (Mr 65, 61, 51.5, 38, and 37 kDa) and the other strain (A.Swiss) expressed six IISP (Mr 59, 57, 54.5, 46, 36, and 34 kDa). No inter-individual intra-strain variations were observed, thus defining strain-associated patterns of IISP (PRP).

Initial sequencing and comparative analysis of the mouse genome

The sequence of the mouse genome is a key informational tool for understanding the contents of the human genome and a key experimental tool for biomedical research. Here, we report the results of an international collaboration to produce a high-quality draft sequence of the mouse genome. We also present an initial comparative analysis of the mouse and human genomes, describing some of the insights that can be gleaned from the two sequences. We discuss topics including the analysis of the evolutionary forces shaping the size, structure and sequence of the genomes; the conservation of large-scale synteny across most of the genomes; the much lower extent of sequence orthology covering less than half of the genomes; the proportions of the genomes under selection; the number of protein-coding genes; the expansion of gene families related to reproduction and immunity; the evolution of proteins; and the identification of intraspecies polymorphism.

Three novel SMR1-related cDNAs characterized in the submaxillary gland of mice show extensive evolutionary divergence in the protein coding region

We have previously characterized an abundant male-specific mRNA from the submaxillary gland (SMG) of rats, encoding the SMR1 (androgen-regulated) protein, which has the structure of a prohormone and is processed by maturation enzymes to release a small peptide in the blood and saliva. We have now characterized three SMR1-related cDNAs in the SMG of Balb/c mice. These cDNAs encode three novel proteins, designated MSG1, MSG2 and MSG3. They are 639, 662 and 471 nucleotides (nt) long, respectively, and the corresponding mRNAs appear to be expressed only in the SMG. The putative polypeptides they encode carry an N-terminal secretory peptide sequence and are, therefore, presumably secreted into saliva. Although closely related, the three mRNAs show striking differences: a particularly different expression pattern and an extremely high degree of variability observed in the central part of the molecules. The MSG1 and MSG3 cDNAs are identical, except for a 173-bp insert found only in MSG1. This insert contains three Pro-rich repeats (GPGIGRPPPPPP), reminiscent of the most abundant multigenic family of the SMG, the Pro-rich proteins (PRP). Although MSG1 shares several common features with PRP, it is structurally related to SMR1. The unusually high ratio of replacement/silent nt changes provides a basis to address complex aspects concerning the molecular events leading to the emergence of new proteins in the SMG.

Molecular cloning and analysis of the protein modules of aggrecans

The large aggregating chondroitin sulfate proteoglycan of cartilage, aggrecan, has served as a prototype of proteoglycan structure. Molecular cloning has elucidated its primary structure and revealed both known and unknown domains. To date the complete structures of chicken, rat and human aggrecans have been deduced, while partial sequences have been reported for bovine aggrecan. A related proteoglycan, human versican, has also been cloned and sequenced. Both aggrecan and versican have two lectin domains, one at the amino-terminus which binds hyaluronic acid and one at the carboxyl-terminus whose physiological ligand is unknown. Both lectins have homologous counterparts in other types of proteins. Within the aggrecans the keratan sulfate domain may be variably present and also has a prominent repeat in some species. The chondroitin sulfate domain has three distinct regions which vary in their prominence in different species. The complex molecular structure of aggrecans is consistent with the concept of exon shuffling and aggrecans serve as suitable prototypes for comprehending the evolution of multi-domain proteins.

Cloning a pseudogene and cDNA encoding a 17-kDa ribosomal protein from mouse: structure and regulation of expression

An rp lambda 5 cDNA encoding a ribosomal protein (r-protein) and a pseudogenic form of the corresponding gene (rp lambda 7) have been cloned from mouse. This cDNA codes for a highly basic protein of 160 amino acids (aa) with a deduced M(r) of 17,601, and most likely represents the species homolog of a recently cloned rat cDNA, which has been proposed to encode a homolog of the yeast r-protein, YL43. The entire rp lambda 5 gene encompasses less than 1.5 kb of genomic DNA and apparently is composed of only two exons, as deduced from sequence comparison with its very similar pseudogenic variant, rp lambda 7. Southern analysis, using the rp lambda 5 cDNA as a probe, indicates the existence of a great number of highly related sequences in the mouse genome. The mRNA for rp lambda 5 is approximately 800 nucleotides (nt) long and is found to be ubiquitously expressed at high levels in embryonic and adult mouse tissues, as shown by Northern and in situ analyses. Retinoic acid (RA) seems to have a moderate down-regulatory effect on this mRNA in differentiating P19 embryonal carcinoma cells. Several degenerate/nondegenerate RA-response element (RARE) motifs are found within 560 bp upstream from the degenerate start codon in rp lambda 7. However, it is unknown whether this RA effect is exerted at the transcriptional and/or posttranscriptional levels.

Molecular cloning and analysis of the protein modules of aggrecans

The large aggregating chondroitin sulfate proteoglycan of cartilage, aggrecan, has served as a prototype of proteoglycan structure. Molecular cloning has elucidated its primary structure and revealed both known and unknown domains. To date the complete structures of chicken, rat and human aggrecans have been deduced, while partial sequences have been reported for bovine aggrecan. A related proteoglycan, human versican, has also been cloned and sequenced. Both aggrecan and versican have two lectin domains, one at the amino-terminus which binds hyaluronic acid and one at the carboxyl-terminus whose physiological ligand is unknown. Both lectins have homologous counterparts in other types of proteins. Within the aggrecans the keratan sulfate domain may be variably present and also has a prominent repeat in some species. The chondroitin sulfate domain has three distinct regions which vary in their prominence in different species. The complex molecular structure of aggrecans is consistent with the concept of exon shuffling and aggrecans serve as suitable prototypes for comprehending the evolution of multi-domain proteins.

Salivary proline-rich proteins: biochemistry, molecular biology, and regulation of expression

The proline-rich proteins (PRPs) in mammalian salivary glands are encoded by tissue-specific multigene families whose members have diverged with respect to structure and regulation of expression. PRPs are expressed constitutively in humans, and comprise about [70%] of the total salivary proteins. Families of similar proteins are dramatically increased or induced in parotid and submandibular glands of rats, mice and hamsters by treatment with the [beta-] agonist isoproterenol. Feeding tannins to rats and mice mimics the effects of isoproterenol on the parotid glands. Salivary PRPs may constitute a defense mechanism against tannins and other polyhydroxylated phenols ingested. Putative transcriptional regulatory sequences have been identified in mouse PRP genes.

Macaque salivary proline-rich protein: structure, evolution, and expression

Proline-rich proteins are a family of proteins that exhibit unique features including an unusual high proline content and salivary-specificity. As a major constituent in the salivary secretion of higher primates, proline-rich proteins may have biological roles in oral lubrication and protection. In this article, the genomic structure and regulation by cAMP of one of the macaque salivary proline-rich protein genes, MnP4, is reviewed. The evolution of this multigene family of proteins is also discussed.

cDNA clones for mouse parotid proline-rich proteins. mRNA regulation by isoprenaline and the nucleotide sequence of proline-rich protein cDNA MP5

cDNA clones for mRNA sequences regulated by isoprenaline in mouse parotid glands were identified by differential colony hybridisation and all hybridised to a diagnostic proline-rich protein (PRP) oligonucleotide. They were divided into two cross-hybridisation groups, A and B, which were shown by hybrid-selected translations to encode acidic PRP and basic PRP, respectively. The A-type subgroup consisted of sequences homologous to the previously identified mouse PRP genes MP2 and MP3. The B-type subgroup comprised clones for the previously identified cDNA pUMP125 (MP4) as well as other PRP sequences. Six of the B-type clones contained a novel PRP cDNA (MP5) and these were sequenced. The composite MP5 cDNA was 897 nucleotides long and contained an open reading frame capable of encoding a 260-residue-long salivary PRP precursor (30% Pro, 19% Gln and 18% Gly), containing nine variant repeat units of consensus PGNQQGPPPQGGPQQ(GPP)R(PPQ). MP5 was 80% identical to the sequence of MP4 and had a high degree of similarity (60%) at its 3'-untranslated region to rat salivary glutamate/glutamine-rich protein (GRP) cDNA. Two MP5 clones contained a 273-bp intron-like insertion in the 3' untranslated region, being derived, therefore, from incompletely spliced MP5 transcripts. Northern blotting showed that, although PRP mRNA species were induced by isoprenaline, a B-type PRP mRNA was present in normal parotid glands. RNA dot-blots probed with PRP-gene-specific oligonucleotides established that MP3, MP4 and MP5 PRP mRNA were all induced by isoprenaline.

Gene sequence of mouse B-type proline-rich protein MP4. Transcriptional start point and an upstream phylogenetic footprint with ets-like and rel/NFkB-like elements

A mouse genomic B-type proline-rich protein (PRP) cosmid clone was isolated by cDNA hybridisation and mapped, the gene region was subcloned and 3770 bp were sequenced. This gene (MP4) contained three introns and encoded a 1020-nt (nt, nucleotide) mRNA for a PRP precursor 300 amino acids long arranged with 11 imperfect 18-residue proline-rich repeats. The transcriptional start point was determined by S1 nuclease mapping and primer extension to be 26 bp downstream of a TATAA sequence. Sequence comparisons revealed that only two regions from positions -650 bp - -30 bp were highly conserved in all other PRP genes, PRP boxes 1 and 2. Box 1 at positions -112 to -135 contained ets-like and rel/NFkB-like elements and was 74% conserved over 23 bp. Box 2 at positions -33 - -51 was 53% conserved over 19 bp. A search of the EMBL and GenBank sequence libraries indicated that PRP box 1 was only present upstream of the known mammalian PRP gene sequences and was absent from other genes. These conserved sequences may thus be relevant to the tissue-specific and beta-adrenergic regulation of PRP gene transcription.

Spontaneous mutation at the hypervariable mouse minisatellite locus Ms6-hm: flanking DNA sequence and analysis of germline and early somatic mutation events

Hypervariability at minisatellite loci is maintained by spontaneous mutation to new-length alleles. At the most variable loci, mutation rate is directly measurable by pedigree analysis. The mouse minisatellite locus Ms6-hm has a germline mutation rate of 2.5% per gamete and is therefore one of the most unstable loci yet identified in the mouse genome. Mutation events at this locus also occur during early mouse development, resulting in mice mosaic for cells carrying a common non-parental allele in different somatic tissues and the germline. The DNA sequence flanking Ms6-hm is rich in dispersed repetitive elements; the minisatellite array has expanded from within a member of the Mouse Transcript family which is flanked by two additional Mouse Transcript elements, and a B2 element lies further 3' to the minisatellite. To define the characteristics of mutation events at Ms6-hm we have analysed 19 germline and 13 somatic length-change events. Germline mutation events at Ms6-hm are not accompanied by the exchange of flanking markers in three informative mutant alleles analysed.

Molecular genetic linkage maps of mouse chromosomes 4 and 6

We have generated a moderate resolution genetic map of mouse chromosomes 4 and 6 utilizing a (C57BL/6J x Mus spretus) F1 x Mus spretus backcross with RFLPs for 31 probes. The map for chromosome 4 covers 77 cM and details a large region of homology to human chromosome 1p. The map establishes the breakpoints in the mouse 4-human 1p region of homology to a 2-cM interval between Ifa and Jun in mouse and to the interval between JUN and ACADM in human. The map for mouse chromosome 6 spans a 65-cM region and contains a large region of homology to human 7q. These maps also provide chromosomal assignment and order for a number of previously unmapped probes. The maps should allow the rapid regional assignment of new markers to mouse chromosomes 4 and 6. In addition, knowledge of the gene order in mouse may prove useful in determining the gene order of the homologous regions in human.

Sequence and expression of the MnP4 gene encoding basic proline-rich protein in macaque salivary glands

We report here the macaque MnP4 cDNA and genomic sequences which encode a basic proline-rich protein (PRP), which is synthesized in macaque parotid gland and submandibular gland. The locations of intron positions and the prototype of the tandem 20-amino-acid repeat motif with the sequence, PPPPGKPQGPPQQGGNKPQG, in MnP4, were compared to those in related genes encoding PRP and glutamic/glutamine-rich proteins (GRP) in humans and rodents. Exceedingly high homology of the first exon and 40-bp region immediately upstream of exon I is observed with other PRP genes of all species studied. In order to identify the regulatory elements involved in control of MnP4 gene expression, a rat submandibular gland-derived cell line (RSMT-A5) was transfected with MnP4-cat constructs that contained the promoter and 5'-flanking regions of the macaque MnP4 gene fused to the bacterial cat gene. Deletion analysis revealed that putative positive and negative regulatory elements reside between nucleotides (nt) -107 and +5, and nt -586 and -108, respectively. As part of this study, the promoter of the macaque MnP4 gene appears to be salivary gland specific. This salivary gland-specific gene expression attests to the complexity of transcriptional regulation in eukaryotes.

Molecular characterization of rat multigene family encoding proline-rich proteins

Three members of the rat proline-rich protein multigene family have been characterized. Each of these genes, RP4, RP13, and RP15, contains three exons and they are approximately 4.8, 5.7, and 5.4 kb, respectively. The DAN sequences of RP4 and RP13 are greater than 93% homologous in the 3.1-kb segment extending from the 5'-upstream region (approximately nucleotide -930) to 238 nucleotides after the second exon/intron junction; however, regions further downstream, intron II and exon III, share less than 43% identity. In contrast, exon III from RP15, RP13, and the previously sequenced mouse PRP gene MP2 are more than 73% conserved. These analyses suggest that the duplication of the ancestral genes to RP13 and RP4 occurred prior to the divergence of the rat PRP genes. The results also indicate that in the past 21.5 million years, multiple recombination events have resulted in a very high degree of divergence among intron II and exon III of RP4 and RP13. This divergence is due in part to the insertion of members of the rat long interspersed repeat DNA family at -930 bp upstream from the transcription initiation site and within intron II of RP13. Comparisons of the nucleotide sequences and organization of exon I with the genomic organization of PRP and glutamic acid/glutamine-rich protein genes in this and previous studies reveal striking resemblance among these genes. These observations are consistent with the notion that this super multigene family arose from duplication of progenitor genes via unequal crossing over events. In addition, the results suggest that concerted evolution has occurred within the tandemly repeated motif of exon II.

Genetic regulation of salivary proteins in rodents

The presence of a protein in the cell is the result of a complex pathway that is known by the term gene expression. In this article we review the existing literature on the structure and expression of representative salivary gland genes and their regulated expression during development and upon extracellular stimulation. The expression of one of the "nuclear" protooncogenes, c-fos, in rat parotid glands is also discussed. Finally, we present some suggestions for future studies that will help to understand the mechanisms leading to gene regulation in rat salivary glands.

mRNAs for PRPs, statherin, and histatins in von Ebner's gland tissues

A search was made for expression of genes for proline-rich proteins (PRPs) and other salivary-type proteins, including statherin and histatins, in taste-bud tissues of mice and primates because of previous genetic findings in mice (Azen et al., 1986) that Prp and taste genes for certain bitter substances are either the same or closely linked. Taste-bud tissues and other tissues were tested for specific mRNAs with labeled DNA probes by Northern blotting and in situ hybridization. It was found that PRP mRNAs were present in von Ebner's glands of mice and macaques, and that there was a much greater degree of PRP mRNA induction in mouse parotid (16-fold) than in von Ebner's gland (two-fold) after in vivo isoproterenol stimulation. This difference may be due, in part, to differences in autonomic nerve innervation. Statherin and histatin mRNAs were found in macaque taste-bud tissues containing von Ebner's gland, and statherin protein was found in human von Ebner's gland by immunohistochemistry. The finding of PRP gene expression in von Ebner's gland, whose secretions have been suggested to play a role in taste stimulation, adds further support to a possible function of PRPs in bitter tasting. The possible functions of statherin and histatins in von Ebner's gland secretions may be related to statherin's regulation of salivary calcium and histatins' antibacterial and antifungal properties.

Prp (proline-rich protein) genes linked to markers Es-12 (esterase-12), Ea-10 (erythrocyte alloantigen), and loci on distal mouse chromosome 6

The closely linked proline-rich protein (Prp) genes, coding for abundant salivary proteins, are located on distal mouse chromosome 6. They are part of a conserved linkage group that is represented on human chromosome 12p. Two other markers, Ea-10 and Es-12, that were previously unassigned to a chromosome are closely linked to Prp genes in the mouse.