DNA divergence in and around the alcohol dehydrogenase locus in five closely related species of Hawaiian Drosophila

The alcohol dehydrogenase (Adh) region from five planitibia subgroup species of Hawaiian picture-wing Drosophila has been cloned. A total of 15 kb of DNA in and around the Adh gene has been compared among the five species. Genetic distances were calculated to determine evolutionary relationships. These distances agree with previous distances determined by protein polymorphism and DNA hybridization techniques and can be interpreted in terms of specific island colonization and speciation (founder) events over the past 5 Myr. Examination of the restriction maps of the cloned Adh region from the five species shows many instances of small deletions, insertion of a transposable element in D. heteroneura, and the existence of a highly variable region on the 3' side of the Adh gene. Clustering relationships and rates of DNA change are calculated and compared with the relationship found for other species of Drosophila.      

A premature stop codon in the ADAMTS2 gene is likely to be responsible for dermatosparaxis in Dorper sheep

We have used polymerase chain reaction-single-strand conformational polymorphism analysis to investigate variation in exon 2 of the ADAM metalloproteinase with thrombospondin type I motif, 2 (ADAMTS2) gene in 598 sheep, including three white Dorper lambs that had a pathology consistent with dermatosparaxis. Four sequence variants (A, B, C and D) were identified at this exon, with the lambs having the dermatosparaxis phenotype being uniquely B homozygous and their mothers being B-containing heterozygous for ADAMTS2. Analysis of the amplified exon 2 sequences revealed the B variant had a nucleotide substitution that creates a premature stop codon and would notionally abbreviate the ADAMTS2 peptide. The B variant was not found in any other breed aside from the white Dorper sheep that were studied.     

The early adaptive evolution of calmodulin

Interaction between gene duplication and natural selection in molecular evolution was investigated utilizing a phylogenetic tree constructed by the parsimony procedure from amino acid sequences of 50 calmodulin- family protein members. The 50 sequences, belonging to seven protein lineages related by gene duplication (calmodulin itself, troponin-C, alkali and regulatory light chains of myosin, parvalbumin, intestinal calcium-binding protein, and glial S-100 phenylalanine-rich protein), came from a wide range of eukaryotic taxa and yielded a denser tree (more branch points within each lineage) than in earlier studies. Evidence obtained from the reconstructed pattern of base substitutions and deletions in these ancestral loci suggests that, during the early history of the family, selection acted as a transforming force on expressed genes among the duplicates to encode molecular sites with new or modified functions. In later stages of descent, however, selection was a conserving force that preserved the structures of many coadapted functional sites. Each branch of the family was found to have a unique average tempo of evolutionary change, apparently regulated through functional constraints. Proteins whose functions dictate multiple interaction with several other macromolecules evolved more slowly than those which display fewer protein-protein and protein-ion interactions, e.g., calmodulin and next troponin-C evolved at the slowest average rates, whereas parvalbumin evolved at the fastest. The history of all lineages, however, appears to be characterized by rapid rates of evolutionary change in earlier periods, followed by slower rates in more recent periods. A particularly sharp contrast between such fast and slow rates is found in the evolution of calmodulin, whose rate of change in earlier eukaryotes was manyfold faster than the average rate over the past 1 billion years. In fact, the amino acid replacements in the nascent calmodulin lineage occurred at residue positions that in extant metazoans are largely invariable, lending further support to the Darwinian hypothesis that natural selection is both a creative and a conserving force in molecular evolution.      

Haplotypic Diversity Within the Ovine Calpastatin <Emphasis Type="Italic">(CAST)</Emphasis> Gene

Calpastatin (CAST) is a protein inhibitor that acts specifically on calpains and plays a regulatory role in postmortem beef tenderization and muscle proteolysis. Polymorphisms in the bovine CAST gene have been associated with meat tenderness, but little is known about how the ovine CAST gene may affect sheep meat quality traits. In this study, we selected two parts of the ovine CAST gene that have been previously reported to be polymorphic (region 1—part of intron 5 and exon 6, and region 2—part of intron 12), to investigate haplotype diversity across an extended region of the ovine gene. First, we developed a simple and efficient polymerase chain reaction-single-strand conformational polymorphism (PCR-SSCP) method for genotyping region 2, which allowed the detection of a novel allele as well as the three previously reported alleles. Next, we genotyped both regions 1 and 2 of the ovine CAST gene from a large number of sheep to determine the haplotypes present. Nine different haplotypes were found across this extended region of the ovine CAST gene and four haplotypes were identified that suggested historical recombination events within this gene. Haplotypes are typically more informative than single nucleotide polymorphisms (SNPs) for analyzing associations between genes and complex production traits, such as meat tenderness, but the potential for intragenic recombination within the ovine CAST may make finding associations challenging.     

Dichelobacter nodosus, Fusobacterium necrophorum and the epidemiology of footrot

Footrot is a debilitating disease of sheep resulting in lameness, production losses and suffering. To study the basic bacteriology of the disease, a survey was initiated across commercial farms and non-commercial research flocks to compare the bacteriology of symptomatic footrot infected sheep with healthy asymptomatic sheep. Of the 80 farmers initially contacted, 14 collected hoof swabs and returned the swabs by post. Following DNA extraction, species-specific PCR was used to identify if Dichelobacter nodosus (D. nodosus) or Fusobacterium necrophorum (F. necrophorum) species were present on each swab. Of the 42 swabs taken from symptomatic footrot infected sheep, 17 were positive for both F. necrophorum and D. nodosus, two were positive for F. necrophorum only, two for D. nodosus only and 23 swabs were negative for both F. necrophorum and D. nod osus. Of the 50 swabs received from healthy asymptomatic sheep, one was positive for F. necrophorum only and 49 were negative for both D. nodosus and F. necrophorum. This suggests that both F. necrophorum and D. nodosus are linked to footrot in the field in a pastoral farming system. If these bacteria are linked together and collectively cause footrot, this may need to be considered when managing a footrot outbreak, or maintaining a quarantine.