William S. Davidson

Mutations in MKKS cause obesity, retinal dystrophy and renal malformations associated with Bardet-Biedl syndrome

Bardet-Biedl syndrome (BBS) is an autosomal recessive disorder predominantly characterized by obesity, retinal dystrophy, polydactyly, learning difficulties, hypogenitalism and renal malformations, with secondary features that include diabetes mellitus, endocrinological dysfunction and behavioural abnormalities. Despite an initial expectation of genetic homogeneity due to relative clinical uniformity, five BBS loci have been reported, with evidence for additional loci in the human genome; however, no genes for BBS have yet been identified. We performed a genome screen with BBS families from Newfoundland that were excluded from BBS1–5 and identified linkage with D20S189. Fine-mapping reduced the critical interval to 1.9 cM between D20S851 and D20S189, encompassing a chaperonin-like gene. Mutations in this gene were recently reported to be associated with McKusick-Kaufman syndrome (MKKS; ref. 8). Given both the mapping position and clinical similarities of these two syndromes, we screened MKKS and identified mutations in five Newfoundland and two European-American BBS pedigrees. Most are frameshift alleles that are likely to result in a non-functional protein. Our data suggest that a complete loss of function of the MKKS product, and thus an inability to fold a range of target proteins, is responsible for the clinical manifestations of BBS.

Polymerase chain reaction/direct sequence analysis of the cytochrome b gene in Salmo salar

Abstract The polymerase chain reaction (PCR) and direct sequencing were used to determine the amount of genetic variation in a 295 nucleotide region of the mitochondrial cytochrome b gene of Atlantic salmon ( Salmo salar ). Sixty salmon from nineteen populations, eleven from Europe and eight from North America, were surveyed at this locus. Three genotypes, which differed from each other at either one or two nucleotide positions, were found. Only one genotype was present among the European populations whereas all three genotypes were observed among the North American populations. These results indicate a very low level of intraspecific variation in Atlantic salmon. This is in accordance with findings observed using other biochemical genetic procedures such as mitochondrial DNA restriction fragment analysis and protein electrophoresis. Brown trout ( Salmo trutta ) differed from Atlantic salmon by a maximum of sixteen nucleotide differences over this region. These included fourteen transitions and two transversions, representing 5.4% sequence divergence between the species. Fifteen of the differences were located at third codon positions and one was a first-position change. The amino acid sequences were identical in both species.

Genetic structure of thick-billed murre (Uria lomvia) populations examined using direct sequence analysis of amplified DNA

Recent research has revealed that the extent of genetic differentiation of animal populations varies greatly (reviewed by Avise et al., 1987), and appears to be negatively correlated with dispersal capability (Ball et al., 1988). Most birds are highly mobile, and correspondingly most avian populations have little if any genetic structuring (e.g., see review by Evans, 1987; also Tegelstrom, 1987; Ball et al., 1988). However, many avian species exhibit strong natal philopatry, and genetic differentiation of demes within some species is substantial, despite high dispersal capabilities (e.g., Canada geese, Branta canadensis; Van Wagner and Baker, 1986; Shields and Wilson, 1987; black brant, B. bernicla; Shields, 1990; fairy prions, Pachyptila turtur; Ovenden et al., 1991). Most previous population genetics studies of birds involved protein electrophoresis, which may not be sufficiently sensitive to detect genetic structuring in many cases. Because mitochondrial DNA (mtDNA) is haploid and maternally inherited, its effective population size is 1/4 that of nuclear genes. MtDNA is therefore affected by founder effects, bottlenecks, and genetic isolation more than are nuclear genes (Birky et al., 1983; Wilson et al., 1985). MtDNA also evolves more quickly than do nuclear-encoded proteins (Brown et al., 1979; Wilson et al., 1985), and although mtDNA analyses are based on only one locus, restriction endonuclease studies of mtDNA have proven more sensitive than protein electrophoresis in detecting genetic structure in many animal species, particularly birds (e.g., Ovenden et al., 1987; Shields and Wilson, 1987; Shields, 1990). Restriction analyses however miss many mutations, such as multiple substitutions within single

Population differentiation and evolution in the common guillemot Uria aalge

Common (Uria aalge) and Brünnichs guillemots (U. Iomvia) are colonial seabirds that nest in temperate to arctic oceans throughout the Northern hemisphere. They are very similar in the characteristics of ecology, demography and life history that are thought to determine the extent of differentiation among populations, yet geographic variation in morphology is notably greater in common guillemots. Despite evidence of strong natal philopatry, previous analyses of allozymes and the mitochondrial cytochrome b gene revealed little genetic differentiation among North Atlantic colonies of Brünnichs guillemots. To determine if the more extensive morphological variability in common guillemots reflects greater genetic variability, we sequenced part of the cytochrome b gene for 160 common guillemots from 10 colonies distributed throughout the Northern hemisphere. Genotype frequencies and phylogenetic relationships among genotypes both indicated that Atlantic and Pacific populations are genetically distinct. Genetic divergence among genotypes suggested that differentiation of these populations has resulted from separation by Pleistocene glaciers and the Bering Landbridge, as well as by currently unsuitable breeding habitat in the Arctic Ocean. Cytochrome b genotype frequencies also differed among Atlantic colonies, and appeared to define a cline similar to that described for morphological characters. Analyses of sequence variation suggested that this variation probably results from secondary contact between two refugial populations from the Pleistocene glaciations, rather than from isolation by distance or selection. In contrast, the Atlantic population of Brünnichs guillemots appears to have arisen through recent expansion of a single homogeneous refugial population.

Palmitate-binding, serum albumin-like proteins in salmonids

There has been considerable controversy over the existence of serum albumin in fish. One of the physiological functions of albumin is to bind free fatty acids. This characteristic was used to screen the plasma of seven species of salmonids. Each species contains a protein fraction that (i) binds palmitate, (ii) has a molecular mass similar to that of human serum albumin, and (iii) is one of the most rapidly migrating proteins when salmonid plasma is subjected to anodal polyacrylamide gel electrophoresis. We conclude therefore, that salmonids have serum albumins that are homologous to the serum albumin of higher vertebrates.

Artificial hybridization of Newfoundland brown trout and Atlantic salmon: hatchability, survival and growth to first feeding

Abstract The relative viability of hybrids produced using anadromous brown trout, Atlantic salmon grilse and sexually mature Atlantic salmon parr from a Newfoundland river was investigated. The sperm of sexually mature salmon performed equally well compared to anadromous salmon sperm when fertilizing both salmon and trout eggs. Hatching success was high in all crosses and controls. By first feeding, hybrids produced using brown trout eggs had suffered higher mortality and were smaller in size than the reciprocal hybrid and both parental controls. Hybrids produced using salmon eggs exhibited high viability and by first feeding were greater in size than both parental controls. A comparison of hatching time and length of hatching period suggests a paternal influence in embryo development. Possible reasons for the differences between reciprocal hybrids and the significance of results with respect to aquaculture are discussed.

The genome ofEntomophaga aulicae (Entomophthorales, Zygomycetes): Base composition and size

The DNA of the fungusEntomophaga aulicae was examined to obtain preliminary information on the genetic apparatus of a potentially important biological control agent and to investigate the hypothesis that the presence of an extensive amount of condensed chromatin in its nucleus is correlated with an unusually large genome. From thermal denaturation studies the base composition of the DNA was determined to be 38% G + C. The DNA content of protoplast nuclei was determined by two independent techniques. The results indicate that the haploid genome size ofE. aulicae is two orders of magnitude greater than that generally attributed to members of the Fungi. This is supported by ultrastructural observations which show large amounts of condensed chromatin in these nuclei. Further ultrastructural evidence suggests that a large mitochondrial DNA pool, polyploidy, and extensive differential replication or gene amplification in protoplast nuclei do not account for the high DNA values reported here.

A Phylogenetic Perspective on the Evolution of Reproductive Behavior in Pagophilic Seals of the Northwest Atlantic as Indicated by Mitochondrial DNA Sequences

The ice-breeding (pagophilic) habits and relatively short lactation periods of several species of “true” seals (Phocidae) of the Northwest Atlantic, including the harp seal ( Pagophilus ), bearded seal ( Erignathus ), and hooded seal ( Cystophora ), usually are assumed to have evolved in parallel. Current taxonomy regards Pagophilus and ringed seals ( Pusa ) along with harbor seals ( Phoca vitulina ) as subgenera of Phoca , unites Phoca (sensu lato) together with gray seals ( Halichoerus ) and Erignathus in the subfamily Phocinae, and places Cystophora with elephant seals ( Mirounga ) in a separate subfamily, Cystophorinae. Cladistic analysis of variation in the DNA sequence of the mitochondrial cytochrome b gene identifies three clades among northern seals: Phoca-Pusa-Halichoerus, Cystophora-Pagophilus , and Erignathus. Erignathus is the sister group to the other species examined. Each clade may be regarded as a tribe of the subfamily Phocinae (the Phocini, Cystophorini, and Erignathini, respectively). The phylogeny suggests that the ice-breeding habit and associated brief lactation are ancestral characters for the Phocinae and that instances of fast-ice or terrestrial breeding are convergences on the ancestral condition in other phocid subfamilies.

Mitochondrial DNA variation in Atlantic capelin, Mallotus villosus: a comparison of restriction and sequence analyses

Divergence estimates were calculated using restriction analysis and cytochrome‐b sequences for capelin Mallotus villosus mitochondrial genomes sampled from Newfoundland and Norwegian populations. On average, pairwise divergence values based on cytochrome‐b sequences were 2.7 times greater than those based on restriction data. Since the rate of evolution in the cytochrome‐b gene is low, it appears that restriction analysis underestimated divergence values, possibly due to limited sensitivity of this method when variable nucleotide positions are not randomly distributed. Mitochondrial genotypes were not shared among the two populations.

A repetitive element in the genome of Atlantic salmon, Salmo salar

When Atlantic salmon (Salmo salar) genomic DNA is digested with the restriction endonuclease BglI and the fragments separated by agarose-gel electrophoresis, bands corresponding to approximately 430 and 923 bp are visualized after EtdBr staining. The 923-bp band was excised from a preparative gel and used to screen a salmon genomic library for recombinant phage (re-phage) containing the repeat. The BglI repeat element is tandemly arrayed, and an array from one re-phage has been sequenced. The BglI repeats comprise 2.3% of the S. salar genome and have been found in the vicinity of rDNA genes (encoding ribosomal RNA). Southern blot hybridization detects a homologue of the Atlantic salmon BglI repeat in the brown trout (Salmo trutta) genome, but not in other salmonids. However, a DNA fragment with sequence homology to part of the BglI repeat has recently been isolated from Arctic charr (Salvelinus alpinus; S.E. Hartley and W.S.D., unpublished data). In addition, the BglI repeat detects RFLPs in Atlantic salmon.