Showing papers by "Stephen J. O'Brien published in 1985"

Genetic basis for species vulnerability in the Cheetah

Abstract: A population genetic survey of over 200 structural loci previously revealed that the South African cheetah (Acinonyx jubatus jubatus) has an extreme paucity of genetic variability, probably as a consequence of a severe population bottleneck in its recent past. The genetic monomorphism of the species is here extended to the major histocompatibility complex, since 14 reciprocal skin grafts between unrelated cheetahs were accepted. The apparent consequences of such genetic uniformity to the species include (i) great difficulty in captive breeding, (ii) a high degree of juvenile mortality in captivity and in the wild, and (iii) a high frequency of spermatozoal abnormalities in ejaculates. The species vulnerability of the cheetah was demonstrated by an epizootic of coronavirus-associated feline infectious peritonitis in an Oregon breeding colony in 1983. Exposure and spread of the coronavirus, which has a very low morbidity in domestic cats (approximately 1 percent), has decimated a heretofore productive and healthy captive population. The extreme genetic monomorphism, especially at the major histocompatibility complex, and the apparent hypersensitivity of the cheetah to a viral pathogen may be related, and provide a biological basis for understanding the adaptive significance of abundant genetic variation in outbred mammalian species.

A molecular solution to the riddle of the giant panda's phylogeny

Abstract: Although it is generally agreed that the giant panda (Ailuropoda melanoleuca) is a member of the order Carnivora, there has long been disagreement over whether it should be classified with bears, raccoons or as a single member of its own family. Four independent molecular and genetic measures lead to a consensus phylogeny for the giant and lesser pandas. The lesser panda diverged from New World procyonids at approximately the same time as their departure from ursids, while ancestors of the giant panda split from the ursid lineage much later, just before the radiation which led to modern bears. The giant panda's divergence was accompanied by a chromosomal reorganization which can be partially reconstructed from the ursid karyotype, but not from that of procyonids or the lesser panda. The apparently dramatic, but actually limited, distinctions between the giant panda and the bears in chromosomal and anatomical morphology provide a graphic mammalian example of the discordance of molecular and morphological (and chromosomal) evolutionary change.

The ets sequence from the transforming gene of avian erythroblastosis virus, E26, has unique domains on human chromosomes 11 and 21: both loci are transcriptionally active.

Abstract: Human DNA segments homologous to the ets region from the transforming gene of avian erythroblastosis virus, E26, were molecularly cloned and shown to be closely related to the viral equivalent by hybridization and partial sequence analysis. The transforming gene of E26 has a tripartite origin with the structure delta gag [1.2 kilobases (kb) from the viral gag gene]-myb(0.9 kb from the chicken myb gene)-ets (1.6 kb from the chicken ets gene). Human ets DNA is located on two distinct human chromosomes. The human ets-1 locus on chromosome 11 encodes a single mRNA of 6.8 kb; the second locus, ets-2 on chromosome 21, encodes three mRNAs of 4.7, 3.2, and 2.7 kb. The ets-related sequences of human DNA on chromosomes 11 and 21 are discontiguous, except for a small overlap region encoding 14 amino acids, where 12 are conserved between these two loci. By contrast, the chicken homolog has contiguous ets-1 and ets-2 sequences and is primarily expressed in normal chicken cells as a single 7.5-kb mRNA. We conclude that the ets sequence shared by the virus, the chicken, and humans is likely to contain at least two dissociable functional domains, ets-1 and ets-2. Thus, the tripartite transforming gene of E26 includes four distinct domains that may be functionally relevant for the transforming function of the virus (delta gag, myb, ets-1, and ets-2).

A molecular phylogeny of the Felidae: immunological distance

Abstract: The phylogenetic distances between 34 of the 37 extant species of Felidae were estimated using albumin immunological distances (AID). Albumins from ten cat species were used to prepare antisera in rabbits. A consensus phylogeny was constructed from a matrix of reciprocal AID measurements using four distinct phylogenetic algorithms. A series of one-way measurements using the ten index antisera and those 24 species for which albumins were available (but antisera were not), permitted addition of these "species' limbs" to the previously derived phylogenetic trees. The major conclusions of the derived topology were: 1) the earliest branch of the feline radiation occurred approximately 12 million years B.P. and led to the small South American cats (ocelot, margay, Geoffroy's cat, etc.); 2) the second branching occurred 8-10 million years B.P. and included the close relatives of the domestic cat (wildcats, jungle cat, sand cat, and black-footed cat) plus Pallas's cat; 3) the third lineage which began to radiate 4-6 million years B.P. was the pantherine lineage, which included several early branches (cheetah, serval, clouded leopard, golden cats, and puma) and a very recent (2 million years B.P.) split between the lynxes and the modern great cats (Panthera). The topology of the Felidae derived from albumin immunological distance is highly consistent with the karyological disposition of these species, as well as with the fossil record of this family. Because of the recent divergence of this group, the presented data set and the derived topology contain certain unresolved phylogenetic relationships which are so indicated.

Organization and chromosomal specificity of autosomal homologs of human Y chromosome repeated DNA.

Abstract: The human Y chromosome contains a group of repeated DNA elements, identified as 3.4-kilobase pair (kb) fragments in Hae III digests of male genomic DNA, which contain both Y-specific and non-Y-specific sequences. We have used these 3.4-kb Hae III Y fragments to explore the organizational properties and chromosomal distribution of the autosomal homologs of the non-Y-specific (NYS) 3.4-kb Hae III Y elements. Three distinct organizations, termed domains, have been identified and shown to have major concentrations on separate chromosomes. We have established that domain K is located on chromosome 15 and domain D on chromosome 16 and suggested that domain R is on chromosome 1. Our findings suggest that each domain is composed of a tandemly arrayed cluster of a regularly repeating unit containing two sets of repeated sequences: one that is homologous to the NYS 3.4-kb Hae III Y sequences and one that does not cross-react with the 3.4-kb Hae III Y repeats. Thus, these autosomal repeated DNA domains, like their Y chromosome counterparts, consist of a complex mixture of repeated DNA elements interspersed among each other in ways that lead to defined periodicities. Although each of the three identified autosomal domains cross-reacts with 3.4-kb Hae III Y fragments purified from genomic DNA, the length periodicities and sequence content of the autosomal domains are chromosome specific. The organizational properties and chromosomal distribution of these NYS 3.4-kb Hae III homologs seem inconsistent with stochastic mechanisms of sequence diffusion between chromosomes.

Biochemical Genetic Variation in Eight Endangered or Threatened Felid Species

Abstract: Electrophoretic variation at 25 biochemical loci was detected in one or more of eight non-domesticated cat species, including representative small cats ( Felis, Leptailurus, Caracal ), the great cats ( Panthera ), and felids of intermediate size ( Leopardus, Neofelis ). In all, 50 distinct polymorphisms are described and each was tested for conformity to Mendelian expectation (in pedigree analysis) and for genetic equilibrium of allelic frequencies. Although most of the variation was detected by alterations in electrophoretic mobility, two isozyme loci showed the presence of “null” alleles (NAD-diaphorase and inorganic pyrophosphatase) in the sampled species. Two subspecies of tigers, Bengal Panthera tigris tigris and Siberian P. tigris altaica , had a different pattern at two loci (glutamate pyruvate transaminase and inorganic pyrophosphatase), which were both polymorphic in Bengal tigers but monomorphic in Siberian tigers. The description of these polymorphisms provides a genetic baseline of potential use in the management and captive breeding of felid populations.

Twenty-Seven Protein Polymorphisms by Two-Dimensional Electrophoresis of Serum, Erythrocytes, and Fibroblasts in Two Pedigrees

Abstract: Twenty-seven independent polymorphic loci were detected by two-dimensional electrophoresis (2DE) of serum, erythrocytes, and fibroblasts in two large families and analyzed for linkage to classical genetic markers. We detected seven serum, four erythrocyte, and 17 fibroblast protein loci that exhibited charge variation in these two families and in a sample of unrelated individuals. The genetic basis of protein variants was confirmed by quantitative gene-dosage dependence and by conformance to Mendelian transmission in the two families, except for four rare variants for which transmission analysis was not possible. Linkage analysis demonstrated that each of the variants represent products of independent loci, with the exception of erythrocyte locus (RBC4), which we also detected in fibroblasts (NC27). Two allozyme polymorphisms, glyoxalase-1 (GLO1) and phosphoglucomutase-3 (PGM3) were specifically identified here based on genotypic concordance and molecular mass. Unknown fibroblast protein (NC22) may be linked to apolipoprotein E (lod score = 2.8 at theta m = theta f = 0), while a serum protein locus (SER1) may be linked to alpha-haptoglobin (lod score = 2.54 at theta m = .20, theta f = .01). Six of seven polymorphic serum loci were previously located on two-dimensional gels: alpha-1 antitrypsin (PI), Gc-globulin (GC), alpha-2 HS glycoprotein (HSGA), alpha-haptoglobin (HP), and two apolipoproteins (APOE and APOA4). Six of 17 polymorphisms detected in fibroblasts were positionally identical to polymorphic loci seen in lymphocytes. These studies indicate a minimum level of average protein charge heterozygosity of approximately 2.2% for the most predominant human cellular proteins and of 5.6% for the most predominant proteins of serum.

Genetic characterization of human c-rel sequences.

Abstract: We isolated and sequenced a human genomic-DNA segment that is homologous to a portion of v-rel, the transforming gene of reticuloendotheliosis virus (strain T). We also localized the human rel sequences to human chromosome 2 by screening a panel of rodent X human somatic-cell hybrids with the newly described human rel segment.

Genetic mapping of endogenous RD-114 retroviral sequences of domestic cats.

Abstract: The RD-114 family of endogenous retroviral sequences in domestic cats has been shown to consist of approximately 20 copies of genetically divergent virogenes per haploid genome. The chromosomal localization for four endogenous sequences (RDV1-4) was accomplished by correlating the occurrence of specific feline chromosomes with diagnostic viral DNA fragments in a panel of cat X rodent somatic cell hybrids. Analysis of the hybrid panel revealed that endogenous RD-114 sequences are dispersed on multiple cat chromosomes, that certain proviral segments are polymorphic with respect to the presence or absence of virus, and that a restriction fragment characteristic of inducible RD-114 resides on a single feline chromosome (B3), probably at a single locus.