Insertion of an endogenous Jaagsiekte sheep retrovirus element into the BCO2 - gene abolishes its function and leads to yellow discoloration of adipose tissue in Norwegian Spælsau (Ovis aries)

Background

The accumulation of carotenoids in adipose tissue leading to yellow fat is, in sheep, a heritable recessive trait that can be attributed to a nonsense mutation in the beta-carotene oxygenase 2 (BCO2) gene. However, not all sheep breeds suffering from yellow fat have this nonsense mutation, meaning that other functional mechanisms must exist. We investigated one such breed, the Norwegian spælsau.

Results

In spælsau we detected an aberration in BCO2 mRNA. Nanopore sequencing of genomic DNA revealed the insertion of a 7.9 kb endogenous Jaagsiekte Sheep Retrovirus (enJSRV) sequence in the first intron of the BCO2 gene. Close examination of its cDNA revealed that the BCO2 genes first exon was spliced together with enJSRV-sequence immediately downstream of a potential -AG splice acceptor site at enJSRV position 415. The hybrid protein product consists of 29 amino acids coded by the BCO2 exon 1, one amino acid coded by the junction sequence, followed by 28 amino acids arbitrary coded for by the enJSRV-sequence, before a translation stop codon is reached.

Conclusions

Considering that the functional BCO2 protein consists of 575 amino acids, it is unlikely that the 58 amino acid BCO2/enJSRV hybrid protein can display any enzymatic function. The existence of this novel BCO2 allele represents an alternative functional mechanism accounting for BCO2 inactivation and is a perfect example of the potential benefits for searching for structural variants using long-read sequencing data.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-07826-5.

A frameshift mutation in the coding region of the myostatin gene (MSTN) affects carcass conformation and fatness in Norwegian White Sheep (Ovis aries)

Mutations in the coding region of the myostatin gene (MSTN) are known to cause an increased muscle mass (IMM) phenotype in several mammals, including mice, dogs, cattle and humans. In sheep, a mutation in the 3'-UTR region introducing a microRNA target site has been reported to cause an IMM-like phenotype because of downregulation of translation. Here we report a novel single base deletion in the coding region of the myostatin gene causing an IMM phenotype in Norwegian White Sheep, characterized by a high carcass conformation class and low fat class (EUROP classification system). The deletion disrupts the reading frame from amino acid (aa) position 320, ending in a premature stop codon in aa position 359. In our material, these MSTN mutations segregated in a pattern showing that they reside in two different haplotypes. The phenotypic effect of the single base deletion is more profound than that of the 3'-UTR mutation.

Validation of test-day models for genetic evaluation of dairy goats in Norway

Test-day data for daily milk yield and fat, protein, and lactose content were sampled from the years 1988 to 2003 in 17 flocks belonging to 2 genetically well-tied buck circles. In total, records from 2,111 to 2,215 goats for content traits and 2,371 goats for daily milk yield were included in the analysis, averaging 2.6 and 4.8 observations per goat for the 2 groups of traits, respectively. The data were analyzed by using 4 test-day models with different modeling of fixed effects. Model [0] (the reference model) contained a fixed effect of year-season of kidding with regression on Ali-Schaeffer polynomials nested within the year-season classes, and a random effect of flock test-day. In model [1], the lactation curve effect from model [0] was replaced by a fixed effect of days in milk (in 3-d periods), the same for all year-seasons of kidding. Models [2] and [3] were obtained from model [1] by removing the fixed year-season of kidding effect and considering the flock test-day effect as either fixed or random, respectively. The models were compared by using 2 criteria: mean-squared error of prediction and a test of bias affecting the genetic trend. The first criterion indicated a preference for model [3], whereas the second criterion preferred model [1]. Mean-squared error of prediction is based on model fit, whereas the second criterion tests the ability of the model to produce unbiased genetic evaluation (i.e., its capability of separating environmental and genetic time trends). Thus, a fixed structure with year (year, year-season, or possibly flock-year) was indicated to appropriately separate time trends. Heritability estimates for daily milk yield and milk content were 0.26 and 0.24 to 0.27, respectively.

Antibacterial and antimalarial properties of peptides that are cecropin-melittin hybrids

Solid phase synthesis was used to produce 5 hybrid peptides containing sequences from the antibacterial peptide, cecropin A, and from the bee venom toxin, melittin. Four of these chimeric peptides showed good antibacterial activity against representative Gram-negative and Gram-positive bacterial species. The best hybrid, cecropin A(1-13)-melittin(1-13) was 100-fold more active than cecropin A against Staphylococcus aureus. It was also a 10-fold better antimalarial agent than cecropin B or magainin 2. Sheep red cells were lysed by melittin at low concentrations, but not by the hybrid molecules, even at 50 times higher concentrations.

Chemical synthesis and enzymic processing of precursor forms of cecropins A and B

Radiolabeled preprocecropin B, with an alpha-amidated COOH terminus, and preprocecropin A, extended at the COOH terminus by a glycine residue, were synthesized by solid-phase methods. The respective syntheses were interrupted at intervals to allow the preparation of the predicted procecropins A and B as well as three other truncated derivatives of the cecropin A precursors. All the synthetic peptides were purified to near homogeneity by reverse-phase liquid chromatography and their purity was established by analytical high performance liquid chromatography, gel electrophoresis, and amino acid analysis. A dipeptidyl aminopeptidase was purified about 350 times from the hemolymph of cecropia pupae and characterized by its affinity for different substrates and inhibitors. The synthetic prepro peptides were tested for processing by an extract of dog pancreas microsomes and purified leader peptidase from Escherichia coli, with and without partly purified dipeptidyl aminopeptidase, and the two synthetic proforms were also processed with the dipeptidyl aminopeptidase alone. From these experiments we conclude that the signal/leader peptidase cleaves the peptide bond between Ala-5 and Ala-4. This cleavage site is further substantiated by radio sequencing of procecropin A isolated after synthesis in a coupled system for in vitro transcription, translation, and processing. The two procecropins, which are stable to further digestion by the signal peptidase, are further processed by dipeptidyl aminopeptidase which removes, in two steps, the dipeptides Ala-Pro (residues -4 and -3) and Glu-Pro (residues -2 and -1). Although the synthetic peptide with only one dipeptide (Glu-Pro) preceding the mature cecropin sequence could function as a substrate for dipeptidyl aminopeptidase, it could be demonstrated as an intermediate in the enzymatic reaction with the procecropins. Dipeptidyl aminopoptidase did not cleave the procecropin analog when it was preceded by a single alanine residue, i.e. preprocecropin (-5,38). Antibacterial activity was demonstrated for the mature cecropin A-Gly obtained by processing of the synthetic preproprotein.

Effects on electrophoretic mobility and antibacterial spectrum of removal of two residues from synthetic sarcotoxin IA and addition of the same residues to cecropin B

Cecropin B and cecropin IA (sarcotoxin IA) are 35- and 39-residue antibacterial peptides from a silk moth and a meat fly, respectively. Using solid phase synthesis we have made these peptides as well as two 37-residue analogs, one containing a deletion of leucine and lysine (residues 2a and 2b) as compared to cecropin IA, the other containing an insertion of leucine and lysine at the corresponding place in cecropin B. This addition and removal of a lysine residue did not cause the expected change in electrophoretic mobility. When tested for antibacterial spectra, the insertion analog was found to be as active as the parent compound while the deletion analog had lost most of its antibacterial capacity. In addition it was shown that the C-terminal amide contributes to the broad spectrum properties of the cecropins.

Molecular cloning, cDNA sequencing, and chemical synthesis of cecropin B from Hyalophora cecropia

Two cDNA clones containing coding information for cecropin B from the Cecropia moth (Hyalophora cecropia) were identified by means of a synthetic probe. Sequencing of the two inserts showed that cecropin B is processed from a 62-amino acid residue precursor molecule including a 26-residue leader peptide and a COOH-terminal glycine residue. The latter presumably donates the nitrogen of the amide group present on the COOH-terminal leucine residue of the mature cecropin B. The sequence deduced for the mature cecropin B differed in the COOH-terminal region from the tentative structure previously determined by carboxypeptidase digestion. To settle the discrepancy, cecropin B was synthesized according to the cDNA sequence with an amidated COOH-terminal leucine. Natural and synthetic cecropin B were found to be indistinguishable with respect to electrophoretic mobility and antibacterial activity against seven different bacteria. The COOH-terminal tetrapeptides were isolated from both natural and synthetic cecropin B and found to be indistinguishable. The correct sequence for cecropin B is (formula; see text).

Insect immunity. 11. Simultaneous induction of antibacterial activity and selection synthesis of some hemolymph proteins in diapausing pupae of Hyalophora cecropia and Samia cynthia

We have previously shown that pupae of the giant silkmoth Samia cynthia have a humoral antibacterial activity, which was induced by viable, nonpathogenic gram-negative bacteria (H.G. Boman et al., 1974). We show here that this activity was formed simultaneously with a selective incorporation of amino acids into eight polypeptide chains characterized by their electrophoretic behavior. If actinomycin D or cycloheximide were given at an early time, no antibacterial activity was found. If the inhibitors were given at the time of maximum activity, there was no effect with actinomycin D but a rapid decrease of the activity in the case of cycloheximide. The results imply that the messenger ribonucleic acid was stable, but that at least one protein component was turning over. Hemolymph from immunized pupae of another giant silkmoth, Hyalophora cecropia, was fractionated by ammonium sulfate precipitation. This procedure, together with the isotope distribution after co-electrophoresis in polyarylamide gels, was used for comparing the response to injury and to different infections. Almost identical polypeptide patterns were obtained as a response to an infection with either viable Enterobacter cloacae or Bacillus subtilis. These patterns differed both qualitatively and quantitatively from the injury effect created by an injection as such. There was only a low antibacterial activity in each of the four fractions obtained by ammonium sulfate precipitation. However, a combination of three fractions restored a high killing activity. Fractionation of hemolymph from untreated pupae provided evidence for at least one preexisting factor which stimulated the killing of Escherichia coli. The osmotic pressure of the bacteria contributed to the antibacterial activity towards E. coli, but not towards B. subtitlis. The killing of E. coli was inhibited by liped A and, to a lesser extent, by an inhibitor of proteolytic enzymes. The similarities and differences with the mammalian complement system are discussed.