Structural deviations in a bovine low expression lysozyme-encoding gene active in tissues other than stomach

Duodenases are a small subfamily of ruminant intestinal serine proteases that have undergone a remarkable diversification in cleavage specificity

Ruminants have a very complex digestive system adapted for the digestion of cellulose rich food. Gene duplications have been central in the process of adapting their digestive system for this complex food source. One of the new loci involved in food digestion is the lysozyme c locus where cows have ten active such genes compared to a single gene in humans and where four of the bovine copies are expressed in the abomasum, the real stomach. The second locus that has become part of the ruminant digestive system is the chymase locus. The chymase locus encodes several of the major hematopoietic granule proteases. In ruminants, genes within the chymase locus have duplicated and some of them are expressed in the duodenum and are therefore called duodenases. To obtain information on their specificities and functions we produced six recombinant proteolytically active duodenases (three from cows, two from sheep and one from pigs). Two of the sheep duodenases were found to be highly specific tryptases and one of the bovine duodenases was a highly specific asp-ase. The remaining two bovine duodenases were dual enzymes with potent tryptase and chymase activities. In contrast, the pig enzyme was a chymase with no tryptase or asp-ase activity. These results point to a remarkable flexibility in both the primary and extended specificities within a single chromosomal locus that most likely has originated from one or a few genes by several rounds of local gene duplications. Interestingly, using the consensus cleavage site for the bovine asp-ase to screen the entire bovine proteome, it revealed Mucin-5B as one of the potential targets. Using the same strategy for one of the sheep tryptases, this enzyme was found to have potential cleavage sites in two chemokine receptors, CCR3 and 7, suggesting a role for this enzyme to suppress intestinal inflammation.

Characterization, organization and expression of AmphiLysC, an acidic c-type lysozyme gene in amphioxus Branchiostoma belcheri tsingtauense

The study on lysozymes remains open in amphioxus, a cephalochordate. Here we show the existence of c-type lysozyme gene (AmphiLysC) in amphioxus, first such data in the basal chordates including urochordate and cephalochordate. This is in contrast to the absence of c-type lysozyme genes in urochordate. It is found that there exist two copies of c-type lysozyme genes in amphioxus genome, and their gene organization is similar to vertebrate c-type lysozyme genes with respect to the number and the size of both exons and introns. AmphiLysC possesses main features characteristic of the digestive c-type lysozyme such as lower number of basic amino acids (low pI values) and pH-optimum in acidic range. Moreover, AmphiLysC is predominantly expressed in the gut. These indicate that AmphiLysC is possibly a digestive c-type enzyme. However, the ubiquitous expression of AmphiLysC in non-digestive tissues such as ovaries, testes, notochord, gill and muscle suggests that it may also play a non-digestive role like antibacterial activity. It is highly likely that AmphiLysC is an enzyme with a combined function of digestion and bacteriolysis.

Molecular characterization of lysozyme type II gene in rainbow trout (Oncorhynchus mykiss): evidence of gene duplication

Rainbow trout (Oncorhynchus mykiss) have two types of lysozyme. Type II lysozyme differs from type I by only one amino acid, but only type II lysozyme has significant bactericidal activity. Due to this novel antibacterial property, lysozyme type II appears to be a candidate gene for enhancing disease resistance in fish as well as livestock species. Using polymerase chain reaction the lysozyme type II gene was amplified from genomic DNA isolated from rainbow trout. Two amplified fragments of 2041 and 2589 bp were observed. Sequencing revealed both amplicons were lysozyme genes having nearly identical nucleotide sequences, except the longer fragment has 548 base pairs inserted in intron 2 at nucleotide position 513 and a few point mutations within intron 2. Both versions of trout lysozyme type II gene were comprised of four exons and three introns. We also demonstrated that trout lysozyme is most likely encoded by these two different genes.

Genomic distribution of three promoters of the bovine gene encoding acetyl-CoA carboxylase alpha and evidence that the nutritionally regulated promoter I contains a repressive element different from that in rat

The enzyme acetyl-CoA carboxylase alpha (ACC-alpha) is rate-limiting for the synthesis of long-chain fatty acids de novo. As a first characterization of the bovine gene encoding this enzyme, we established the entire bovine ACC-alpha cDNA sequence (7041 bp) and used experiments with 5' rapid amplification of cDNA ends to determine the heterogeneous composition of 5' untranslated regions, as expressed from three different promoters (PI, PII and PIII). The individual locations of these promoters have been defined within an area comprising 35 kbp on Bos taurus chromosome 19 ('BTA19'), together with the segmentation of the first 14 exons. Primer extension analyses reveal that the nutritionally regulated PI initiates transcription from at least four sites. PI transcripts are much more abundant in adipose and mammary-gland tissues than in liver or lung. A 2.6 kb promoter fragment drives the expression of reporter genes only weakly in different model cells, irrespective of stimulation with insulin or dexamethasone. Thus bovine PI is basically repressed, like its analogue from rat. Finely graded deletions of PI map two separate elements, which have to be present together in cis to repress bovine PI. The distal component resides within a well-preserved Art2 retroposon element. Thus sequence, structure and evolutionary origin of the main repressor of PI in bovines are entirely different from its functional counterpart in rat, which had been identified as a (CA)(28) microsatellite. We show that, in different mammalian species, unrelated genome segments of different origins have been recruited to express as functionally homologous PI the ancient and otherwise highly conserved ACC-alpha-encoding gene.

Mosaic evolution of ruminant stomach lysozyme genes

The genomes of ruminant artiodactyls, such as cow and sheep, have approximately 10 lysozyme genes, 4 of which are expressed in the stomach. Most of the duplications of the lysozyme genes occurred 40-50 million years ago, before the divergence of cow and sheep. Despite this, the coding regions of stomach lysozyme genes within a species (e.g., cow, sheep, or deer) are more similar to each other than to lysozyme genes in other ruminants. This observation suggests that the coding regions of the stomach lysozyme genes have evolved in a concerted fashion. Our previous characterization of 3 cow stomach lysozyme genes suggested that it was only the coding exons that had participated in concerted evolution. To determine whether the introns and flanking regions of ruminant stomach lysozyme genes are evolving in a concerted or a divergent fashion, we have isolated and characterized 2 sheep stomach lysozyme genes. Comparison of the sequences of the sheep and cow stomach lysozyme genes clearly shows that the introns and flanking regions have evolved, like the 3' untranslated region of the mRNAs, in a divergent manner. Thus, if the four coding exons are evolving by concerted evolution, then a mosaic pattern of concerted and divergent evolution is occurring in these genes. The independent concerted evolution of coding exons of the ruminant stomach lysozyme gene may have assisted in the accelerated adaptive evolution of the lysozyme to new function in the early ruminant.