An experimental analysis of the developmental capacities of distal parts of avian leg buds

The development, differentiation, and pattern formation of isolated distal parts of avian leg buds that had grown ectopically on the chorioallantoic membrane (CAM) or in the coelomic cavity were studied. The grafts grown on the CAM invariably gave rise to cartilage and soft connective tissue. In some cases muscle tissue was also found. The CAM grafts did not undergo overt morphogenesis and pattern formation. A high percentage of grafts grown in the coelomic cavity showed a close approximation to normal limbs. The presence of proximal structures depended on the stage of development of the donor at the time of the operation, on the size of the grafts, and on the site to which the graft was attached within the coelom. The presence of anteroposterior structures depended on the shape of the graft. The pattern formation of this axis was found to be independent of the presence of the zone of polarizing activity at the proximal posterior border of the bud. The distance from the tip of the bud to the line of most distal colonization by myogenic cells was determined. The speed of migration of the myogenic cells can be considered to be constant. In muscleless legs, tendons developed at the levels of the phalanges and the tarsometatarse. They degenerated, however, in the absence of muscle from day 9 on, from proximal to distal areas. CAM grafts as well as coelomic grafts were well vascularized. The endothelial cells of the blood vessels were of host origin. In coelomic grafts, nerves were present with Schwann cells of host origin. The nerves and blood vessels showed a distribution that resembled that in normal legs.

Effects of chromosome 17 on features of the metabolic syndrome in the Lyon hypertensive rat

The metabolic syndrome (involving obesity, hypertension, dyslipidemia, insulin resistance, and a proinflammatory/prethrombotic state) is a major risk factor for cardiovascular disease. Its incidence continues to rise, in part because of the epidemic increase in obesity. The Lyon hypertensive (LH) rat is a model for hypertension and several other features of the metabolic syndrome, having high body weight, plasma cholesterol, and triglycerides, increased insulin-to-glucose ratio, and salt-sensitive hypertension. Previous genetic studies in LH/Mav rats and a normotensive control (LN/Mav) identified quantitative trait loci (QTLs) on rat chromosome (RNO)17 for multiple features of the metabolic syndrome. To further evaluate the role of RNO17 in the LH rat, we generated a consomic strain (LH-17(BN)) by substituting LH RNO17 with that of the sequenced Brown Norway (BN/NHsdMcwi) rat. Male LH and BN rats and LH-17(BN) rats were characterized for blood pressure and metabolic and morphological parameters. Similar to the protective effect of LN alleles, the LH-17(BN) rat also showed decreased body weight, triglycerides, and blood pressure; however, there was no significant difference in cholesterol or insulin-to-glucose ratio. Therefore, the substitution of the LH chromosome 17 is sufficient to recapitulate some, but not all, of the traits previously mapped to this chromosome. This could be due to the lack of a susceptible LH genome background or due to the introgression of chromosome 17 from another strain. Regardless, this study provides a single-chromosome genetic model for further dissection of blood pressure and morphological and metabolic traits on this chromosome.

Rat survival to anthrax lethal toxin is likely controlled by a single gene

We examined whether survival of different rat strains administered anthrax lethal toxin is genetically determined. A reproducible test population of first filial generation hybrid rats was bred based on the susceptibility of progenitors to anthrax lethal toxin and to maximize genetic diversity across the strains. These rats were then tested with varying doses of anthrax lethal toxin. We found that all 'sensitive' strains died within 2 h following systemic administration of 240 mug/kg lethal toxin, while one strain survived following a five times higher dose (1.4 mg/kg). The ability of lethal toxin to lyse macrophage cultures derived from the bone marrow of these strains corresponded with in vivo results. We conclude that a rat test population can detect strain differences in response to anthrax lethal toxin. Survival is influenced by the host genome background and is likely due to a single gene with a recessive mode of inheritance.

Synergistic QTL interactions between Rf-1 and Rf-3 increase renal damage susceptibility in double congenic rats

The FHH (fawn-hooded hypertensive) rat is a model of hypertension-associated chronic kidney damage. Five interacting quantitative trait loci (QTLs), named Rf-1-Rf-5, determine the high renal susceptibility. The aim of the present study was to investigate a possible interaction between Rf-1 and Rf-3. Differences in renal susceptibility between ACI (August x Copenhagen Irish) controls, Rf-1A and Rf-3 single congenics, and Rf-1A+3 double congenic rats were assessed using four different treatments: two-kidney control (2K), 2K plus N(omega)-nitro-L-arginine methyl ester (L-NAME)-induced hypertension (2K+L-NAME), unilateral nephrectomy (UNX), and UNX plus L-NAME-induced hypertension (UNX+L-NAME). Proteinuria (UPV) and systolic blood pressure (SBP) were assessed after 6, 12, and 18 weeks, while the incidence of glomerulosclerosis (%FGS) was determined at the end of the experiment. In a separate experiment, renal autoregulation was assessed in 13-15-week old 2K rats of all four strains. Compared to ACI rats, small increases in renal susceptibility were found in Rf-1A and Rf-3 single congenics following 2K+L-NAME, UNX, and UNX+L-NAME treatments. However, in the Rf-1A+3 double congenics, a major increase in renal susceptibility was found with all four treatments. Both Rf-1A and Rf-1A+3 congenic rats had an impaired renal autoregulation. In contrast, the Rf-3 had a normal autoregulation, similar to that of the ACI rat. These findings indicate that Rf-1 and Rf-3 alone slightly increase the susceptibility to the development of renal damage. However, a synergistic interaction between these two QTLs markedly enhances renal susceptibility. In contrast to the Rf-1 region, the Rf-3 region does not carry genes influencing renal autoregulation.

Genetic determinants on rat chromosome 6 modulate variation in the hypercapnic ventilatory response using consomic strains

To understand the genetic basis of pathways involved in the control of breathing, a large scale, high-throughput study using chromosomal substitution strains of rats is underway. Eight new consomic rat stains (SS-2(BN), SS-4(BN), SS-6(BN), SS-7(BN), SS-8(BN), SS-11(BN), SS-12(BN), SS-14(BN), SS-Y(BN)), containing one homozygous BN/NHsdMcwi (BN) chromosome on a background of SS/JrHsdMcwi (SS), were created by PhysGen (http://pga.mcw.edu) Program for Genomic Applications. Male and female rats were studied using standard plethysmography under control conditions and during acute hypoxia (inspired oxygen fraction = 0.12) and hypercapnia (inspired CO(2) fraction = 0.07). The rats were also studied during treadmill exercise. Both male and female BN rats had a significantly lower ventilatory response during 7% CO(2) compared with SS rats of the same gender. SS-6(BN) female rats had a significantly reduced ventilatory response, similar to BN rats due primarily to a reduced tidal volume. Male SS-6(BN) rats had a significantly reduced tidal volume response to hypercapnia but a slightly increased frequency response during hypercapnia. Gene(s) on the Y chromosome may play a role in this increased frequency response in the male rats because the SS-Y(BN) hypercapnic ventilatory response involves a significantly increased frequency response. Several chromosomal substitutions slightly altered the ventilatory responses to hypoxia and exercise. However, genes on chromosomes 6 and Y of those studied are of primary importance in aspects of ventilatory control currently studied.

Consomic rat model systems for physiological genomics

A consomic rat strain is one in which an entire chromosome is introgressed into the isogenic background of another inbred strain using marker-assisted selection. The development and physiological screening of two inbred consomic rat panels on two genetic backgrounds (44 strains) is well underway. Consomic strains enable one to assign traits and quantitative trait loci (QTL) to chromosomes by surveying the panel of strains with substituted chromosomes. They enable the rapid development of congenic strains over a narrow region and enable one to perform F2 linkage studies to positionally locate QTL on a single chromosome with a fixed genetic background. These rodent model systems overcome many of the problems encountered with segregating crosses where even if linkage is found, each individual in the cross is genetically unique and the combination of genes cannot be reproduced or studied in detail. For physiologists, consomics enable studies to be performed in a replicative or longitudinal manner to elucidate in greater detail the sequential expression of genes responsible for the observed phenotypes of these animals. They often provide the best available inbred control strains for physiological comparisons with the parental strains and they enable one to assess the impact of a causal gene region in a genome by allowing comparisons of the effect of replacement of a specific chromosome on a disease susceptible or a resistant genomic background. Consomic rat strains are proving to be a unique scientific resource that can greatly extend our understanding of genes and their role in the regulation of complex function and disease.

Gender-specific genetic determinants of blood pressure and organ weight: pharmacogenetic approach

A total genome scan and pharmacogenetic study were designed to search for genetic determinants of blood pressure (BP) as well as heart and kidney weights. Genome scanning was carried out in 266 F(2) intercrosses from Prague hypertensive hypertriglyceridemic rats for phenotypes of organ weights, baseline BP, BP after blockade of the renin-angiotensin system (RAS) by losartan, of the sympathetic nervous system (SNS) by pentolinium, and of the nitric oxide (NO) synthase by N(G)-nitro-L-arginine methyl ester. Pharmacogenetic analysis showed that, in males, BP was controlled by two loci on chromosomes 1 and 5 (Chr1, Chr5) through the SNS, and these loci showed a positive contribution for relative kidney weight (KW/BW). On the other hand, baseline BP in females was controlled by two loci on Chr3 and Chr7. The effect of these loci was not mediated by the RAS, SNS or NO system. These loci did not show any effect for KW/BW. Negatively-linked loci for KW/BW and relative heart weight (HW/BW) were identified on Chr2 in both genders. Another negatively-linked locus for KW/BW, located on Chr8 in males, affected BP through the SNS. This locus on Chr8 overlapped with a previously-reported modifier locus for polycystic kidney disease (PKD). In conclusion, this pharmacogenetic study determined two loci for BP and relative organ mass implicating sympathetic overactivity. Concordance of the identified locus for KW/BW and BP through the SNS on Chr8 with the PKD locus revealed the importance of this region for renal complications in various diseases.

Mapping baroreceptor function to genome: a mathematical modeling approach

To gain information about the genetic basis of a complex disease such as hypertension, blood pressure averages are often obtained and used as phenotypes in genetic mapping studies. In contrast, direct measurements of physiological regulatory mechanisms are not often obtained, due in large part to the time and expense required. As a result, little information about the genetic basis of physiological controlling mechanisms is available. Such information is important for disease diagnosis and treatment. In this article, we use a mathematical model of blood pressure to derive phenotypes related to the baroreceptor reflex, a short-term controller of blood pressure. The phenotypes are then used in a quantitative trait loci (QTL) mapping study to identify a potential genetic basis of this controller.

A genomic-systems biology map for cardiovascular function

With the draft sequence of the human genome available, there is a need to better define gene function in the context of systems biology. We studied 239 cardiovascular and renal phenotypes in 113 male rats derived from an F2 intercross and mapped 81 of these traits onto the genome. Aggregates of traits were identified on chromosomes 1, 2, 7, and 18. Systems biology was assessed by examining patterns of correlations ("physiological profiles") that can be used for gene hunting, mechanism-based physiological studies, and, with comparative genomics, translating these data to the human genome.

Automated construction of high-density comparative maps between rat, human, and mouse

Animal models have been used primarily as surrogates for humans, having similar disease-based phenotypes. Genomic organization also tends to be conserved between species, leading to the generation of comparative genome maps. The emergence of radiation hybrid (RH) maps, coupled with the large numbers of available Expressed Sequence Tags (ESTs), has revolutionized the way comparative maps can be built. We used publicly available rat, mouse, and human data to identify genes and ESTs with interspecies sequence identity (homology), identified their UniGene relationships, and incorporated their RH map positions to build integrated comparative maps with >2100 homologous UniGenes mapped in more than one species (approximately 6% of all mammalian genes). The generation of these maps is iterative and labor intensive; therefore, we developed a series of computer tools (not described here) based on our algorithm that identifies anchors between species and produces printable and on-line clickable comparative maps that link to a wide variety of useful tools and databases. The maps were constructed using sequence-based comparisons, thus creating "hooks" for further sequence-based annotation of human, mouse, and rat sequences. Currently, this map enables investigators to link the physiology of the rat with the genetics of the mouse and the clinical significance of the human.

The newly inbred cohen diabetic rat: a nonobese normolipidemic genetic model of diet-induced type 2 diabetes expressing sex differences

The newly inbred Cohen diabetic rat is an exceptional experimental model of diet-induced type 2 diabetes mellitus that is the result of secondary inbreeding nearly 30 years after it originally had been established. Animals from the original colony were selectively inbred by stringent criteria for 10 additional generations, bringing overall inbreeding to >50 generations. The metabolic phenotypes of the resulting contrasting strains, designated as the Cohen diabetic-sensitive (CDs) and -resistant (CDr) rats, were characterized. The phenotype of the CDs strain that was fed a regular diet consisted of fasting normoglycemia, normal glucose tolerance to intraperitoneal glucose loading, normal fasting insulin levels, and a normal insulin response to glucose loading. In contrast, CDs rats that were fed a custom-prepared high-sucrose low-copper diabetogenic diet became overtly diabetic: fasting glucose levels were normal or elevated, and the blood glucose insulin response to glucose loading was markedly abnormal. CDr rats that were fed a regular or diabetogenic diet did not develop diabetes and maintained normal glucose tolerance and insulin secretion. A striking sex difference was observed in CDs rats that were fed a diabetogenic diet: males had a lower growth rate and a more severe glucose intolerance pattern than females. Gonadectomy shortly after weaning did not prevent the development of the diabetic phenotype in its early phase in either sex but markedly attenuated its expression in males at a later phase, abolishing the sex differences. Alternate-day feeding, as opposed to daily feeding, also attenuated the metabolic phenotype in males. The development of the diabetic phenotype in CDs rats that were fed a diabetogenic diet was not accompanied by obesity or hyperlipidemia. The genetic profile of the strains was established using 550 microsatellite markers evenly distributed throughout the rat genome. The rate of homozygosity within strain was > or = 96%. The rate of polymorphism between the contrasting strains was 43%. We conclude that the metabolic phenotypes of the rebred colony of CDs and CDr rats and their genetic makeup render the Cohen diabetic rat a useful experimental model that is highly suitable for studying the interaction between nutritional-metabolic environmental factors and genetic susceptibility (sensitivity and resistance) for the development of type 2 diabetes. The model is also distinctively useful for investigating the effect of sex on the expression of the diabetic phenotype.

The genetic basis of plasma variation in adiponectin, a global endophenotype for obesity and the metabolic syndrome

Here we present the first genetic analysis of adiponectin levels, a newly identified adipocyte-derived protein. Recent work has suggested that adiponectin may play a role in mediating the effects of body weight as a risk factor for coronary artery disease. For this analysis we assayed serum levels of adiponectin in 1100 adults of predominantly northern European ancestry distributed across 170 families. Quantitative genetic analysis of adiponectin levels detected an additive genetic heritability of 46%. The maximum LOD score detected in a genome wide scan for adiponectin levels was 4.06 (P = 7.7 x 10(-6)), 35 cM from pter on chromosome 5. The second largest LOD score (LOD = 3.2; P = 6.2 x 10(-5)) was detected on chromosome 14, 29 cM from pter. The detection of a significant linkage with a quantitative trait locus on chromosome 5 provides strong evidence for a replication of a previously reported quantitative trait locus for obesity-related phenotypes. In addition, several secondary signals offer potential evidence of replications for additional previously reported obesity-related quantitative trait loci on chromosomes 2 and 10. Not only do these results identify quantitative trait loci with significant effects on a newly described, and potentially very important, adipocyte-derived protein, they also reveal the emergence of a consistent pattern of linkage results for obesity-related traits across a number of human populations.

Identification of two susceptibility loci for vascular fragility in the Brown Norway rat

A trait of vascular fragility, characterized by the formation of abrupt defects within the elastic laminae of the abdominal aorta, has been identified in Brown Norway (BN) rats. These lesions are greatly exacerbated in F(1) rats from a BN x New Zealand genetically hypertensive (GH) intercross, implying that the genetic background provided by the GH rat influences lesion severity. The F(2) progeny of the BN x GH intercross were used to identify susceptibility loci for the lesions as well as exacerbating loci. Two major quantitative trait loci (QTLs) for number of internal elastic lamina lesions were identified on rat chromosomes 5 and 10, with the maximum "log of the odds ratio" (LOD) scores at D5Rat119 (LOD 5.0) and at D10Mit2 (LOD 4.5), respectively, together contributing 33.5% to the genetic variance. Further analysis revealed that the chromosome 10 locus exhibits a dominant mode of inheritance, with BN alleles being associated with increased lesion number (P < 0.0002) compared with GH homozygotes. This locus was in epistasis to a modifier locus on rat chromosome 2 at D2Mit14 (LOD score 2.12). A second major locus was identified on chromosome 5, exhibiting a semidominant mode of inheritance, again with the BN allele being significantly associated with increased lesion number (P < 0.0001). Furthermore, a locus influencing lesion severity was identified on chromosome 3 wherein GH alleles associated with increased severity. This is the first study to identify susceptibility loci for vascular elastic tissue fragility.

Radiation hybrid mapping of 11 alpha and beta nicotinic acetylcholine receptor genes in Rattus norvegicus

Acetylcholine is the main neurotransmitter of the vestibular efferents and a wide variety of muscarinic and nicotinic acetylcholine receptors are expressed in the vestibular periphery. To date, 11 nicotinic subunits (alpha and beta) have been reported in mammals. Previously, our group [Brain Res. 778 (1997) 409] reported that these nicotinic acetylcholine receptor alpha and beta subunits were differentially expressed in the vestibular periphery of the rat. To begin an understanding of the molecular genetics of these vestibular efferents, this study examined the chromosomal locations of these nicotinic acetylcholine receptor genes in the rat (Rattus norvegicus). Using radiation hybrid mapping and a rat radiation hybrid map server (www.rgd.mcw.edu/RHMAP SERVER/), we determined the chromosomal position for each of these genes. The alpha2-7, alpha9, alpha10, and beta2-4 nicotinic subunits mapped to the following chromosomes: alpha2, chr. 15; alpha3, chr. 8; alpha4, chr. 3; alpha5, chr. 8; alpha6, chr. 16; alpha7, chr. 1; alpha9, chr. 14; alpha10, chr. 7; beta2, chr. 2; beta3, chr. 16; and beta4, chr. 8. With the location for each of these nicotinic subunits known, it is now possible to develop consomic and/or congenic strains of rats that can be used to study the functional genomics of each of these subunits.

Genetic rat models of hypertension: relationship to human hypertension

Experimental models of human disease are frequently used to investigate the pathophysiology of disease as well as the mechanisms of action of therapeutics. However, as long as models have been used there have been debates about the utility of experimental models and their applicability for human disease on the phenotypic and genomic level. The recent advances in molecular genetics and genomics have provided powerful tools to study the genetics of multifactorial diseases, such as hypertension. However, studies of such diseases in humans remain challenging in part due to lack of statistical power and genetic heterogeneity within patient populations. For hypertension, various rat models have been developed and used for the identification of susceptibility loci for genetic hypertension. With the advent of "comparative genomics," the application of genetic studies to both human and animal model systems allows for a new paradigm, where comparative genomics can be used to bridge between model utility and clinical relevance. This review discusses recent approaches in genetics to facilitate gene discovery for polygenic disorders with specific focus on how comparative mapping can be used to select target regions in the human genome for large-scale association studies and linkage disequilibrium testing in clinical populations.

The future of genetic case-control studies

The case-control study design has been a veritable workhorse in epidemiological research since its inception and acceptance as a valid and valued field of inquiry. The reasons for this owe to the simplicity of the required sampling and the (potential) ease of analysis and interpretation of results. Unfortunately, there are a number of problems that plague the use of the case-control design in assessing relationships between genetic variation and disease susceptibility in the population at large. Many of these problems are entirely analogous to problems that inhere in applications of the case-control design in nongenetic settings. These problems include stratification, the assessment of statistical significance, heterogeneity, and the interpretation of multiple outcomes or phenotypic information. In this chapter we describe 10 problems thought to plague genetic case-control studies and offer potential solutions to each. Many of our proposed solutions require the use of multiple DNA markers to accommodate the genetic background of the individuals sampled as cases and controls. It is hoped that our discussions and proposals will spark further debate about the analysis and ultimate utility of the case-control study in genetic epidemiology research.

The use of designer rats in the genetic dissection of hypertension

The rat is a well-established model for hypertension research, in both physiologic and pharmacologic study. Quantitative trait loci (QTL) for blood pressure and related phenotypes have been described on every rat chromosome; therefore, more simplified models must be generated to identify and study the function of the gene(s) located by QTL analysis. Designer rat strains, such as congenic and consomic strains, which share phenotypic and genotypic characteristics with humans but with a greatly simplified genetic background, would yield a powerful platform for functional studies, especially when combined with microarray technologies. Development of these designer rats would result in better-defined disease models that can be used in physiologic and applied pharmacologic studies to better treat human essential hypertension.

Brown Norway chromosome 13 confers protection from high salt to consomic Dahl S rat

Consomic rats (SS.BN13), in which chromosome 13 from normotensive inbred Brown Norway rats from a colony maintained at the Medical College of Wisconsin (BN/Mcw) was introgressed into the background of Dahl salt-sensitive (SS/Mcw) rats, also maintained in a colony at the Medical College of Wisconsin, were bred. The present studies determined the mean arterial pressure (MAP) responses to salt and renal and peripheral vascular responses to norepinephrine and angiotensin II; 24-hour protein excretion and histological analyses were used to assess renal pathology in rats that received a high salt (4% NaCl) diet for 4 weeks. MAP of rats measured daily during the fourth week averaged 170+/-3.3 mm Hg in SS/Mcw rats, 119+/-2.1 mm Hg in SS.BN13 rats, and 103+/-1.3 mm Hg in BN/Mcw rats. After salt depletion, MAP fell an average of 27+/-4.5 mm Hg in SS/Mcw rats, 9+/-2.6 mm Hg in SS.BN13 rats, and 11+/-3.0 mm Hg in BN/Mcw rats. Protein excretion of SS/Mcw rats on a high salt diet averaged 189+/-30 mg/24 h, 63+/-18 mg/24 h in SS.BN13 rats, and 40+/-6.4 mg/24 h in BN/Mcw rats. Compared with SS.BN13 and BN/Mcw rats, SS/Mcw rats exhibited significantly greater increases of renal vascular resistance in response to intravenous norepinephrine and angiotensin II. Severe medullary interstitial fibrosis and tubular necrosis after a high salt diet were found consistently in SS/Mcw rat kidneys but were largely absent in the SS.BN13 and BN/Mcw rat kidneys. A similar degree of glomerular sclerosis was found in both SS/Mcw and SS.BN13 rats. In rats fed a 0.4% salt diet, the glomerular filtration rate of SS/Mcw rats was significantly less than that of BN/Mcw and SS.BN13 rats. These results reveal a powerful gene, or set of genes, within chromosome 13 of BN/Mcw rats that confers protection from the detrimental effects of high salt to the SS/Mcw rats.

Quantitative trait loci on chromosomes 3 and 17 influence phenotypes of the metabolic syndrome

Recent research has emphasized the importance of the metabolic cluster, which includes glucose intolerance, dyslipidemia, and high blood pressure, as a strong predictor of the obesity-related morbidities and premature mortality. Fundamental to this association, commonly referred to as the metabolic syndrome, is the close interaction between abdominal fat patterning, total body adiposity, and insulin resistance. As the initial step in identifying major genetic loci influencing these phenotypes, we performed a genomewide scan by using a 10-centiMorgan map in 2,209 individuals distributed over 507 nuclear Caucasian families. Pedigree-based analysis using a variance components linkage model demonstrated a quantitative trait locus (QTL) on chromosome 3 (3q27) strongly linked to six traits representing these fundamental phenotypes [logarithm of odds (lod) scores ranged from 2.4 to 3.5]. This QTL exhibited possible epistatic interaction with a second QTL on chromosome 17 (17p12) strongly linked to plasma leptin levels (lod = 5.0). Situated at these epistatic QTLs are candidate genes likely to influence two biologic precursor pathways of the metabolic syndrome.

Retinoic acid-induced tissue transglutaminase and apoptosis in vascular smooth muscle cells

Retinoids exert antiproliferative and prodifferentiating effects in vascular smooth muscle cells (SMCs) and reduce neointimal mass in balloon-injured blood vessels. The mechanisms through which retinoids carry out these effects are unknown but likely involve retinoid receptor-mediated changes in gene expression. Here we report the cloning, chromosomal mapping, and biological activity of the retinoid-response gene rat tissue transglutaminase (tTG). Northern blotting studies showed that tTG is rapidly and dose-dependently induced in a protein synthesis-independent manner after stimulation with the natural retinoid all-trans retinoic acid (atRA). The induction of tTG was selective for atRA and its stereoisomers 9-cis and 13-cis RA, because little or no elevation in mRNA expression was observed with a panel of growth factors. Western blotting and immunofluorescence confocal microscopy showed an accumulation of cytosolic tTG protein after atRA stimulation. Radiolabeled cross-linking studies revealed a corresponding elevation in in vitro tTG activity. The increase in tTG activity was reduced in the presence of 2 distinct inhibitors of tTG (monodansylcadaverine and cystamine). atRA-induced tTG mRNA and protein expression were followed by a significant elevation in SMC apoptosis. Such retinoid-induced programmed cell death could be partially inhibited with each tTG inhibitor and was completely blocked when both inhibitors were used simultaneously. These results establish a role for atRA in the sequential stimulation of tTG and apoptosis in cultured SMCs. atRA-mediated apoptosis in SMCs seems to require the participation of active tTG, suggesting a potential mechanistic link between this retinoid-inducible gene and programmed cell death.

High-throughput scanning of the rat genome using interspersed repetitive sequence-PCR markers

We report the establishment of a hybridization-based marker system for the rat genome based on the PCR amplification of interspersed repetitive sequences (IRS). Overall, 351 IRS markers were mapped within the rat genome. The IRS marker panel consists of 210 nonpolymorphic and 141 polymorphic markers that were screened for presence/absence polymorphism patterns in 38 different rat strains and substrains that are commonly used in biomedical research. The IRS marker panel was demonstrated to be useful for rapid genome screening in experimental rat crosses and high-throughput characterization of large-insert genomic library clones. Information on corresponding YAC clones is made available for this IRS marker set distributed over the whole rat genome. The two existing rat radiation hybrid maps were integrated by placing the IRS markers in both maps. The genetic and physical mapping data presented provide substantial information for ongoing positional cloning projects in the rat.

Localization of a small genomic region associated with elevated ACE

Defining the relationship between multiple polymorphisms in a small genomic region and an underlying quantitative trait locus (QTL) represents a major challenge in human genetics. Pedigree analyses have shown that angiotensin I-converting enzyme (ACE) levels are influenced by a QTL located within or close to the ACE gene and most likely resides in the 3' region of this locus. We genotyped seven polymorphisms spanning 13 kb in the 3' end of ACE in 159 Afro-Caribbean subjects to evaluate the linkage disequilibrium between these sites and to narrow the genomic region associated with an elevated ACE level using a cladistic analysis. The linkage disequilibrium measurement D' and a haplotype tree revealed three distinct haplotype segments, presumably because of recombination. The value of the linkage disequilibrium parameter p(excess) was highest for site 22982, which is located in the middle segment. A series of nested, cladistic analyses confirmed that the other two regions are unlikely to be the ACE-linked QTL and that the variant resides in the middle region. Analyses of the same polymorphisms in 98 unrelated Europeans in the Monitoring Trends and Determinants in Cardiovascular Diseases (MONICA) study resulted in fewer haplotypes than were observed among the Afro-Caribbean subjects, suggesting that populations with greater genetic diversity may be especially informative for fine-scale mapping.

Early development of the müllerian duct in avian embryos with reference to the human. An ultrastructural and immunohistochemical study

In vertebrates, the female reproductive system arises from the Müllerian (paramesonephric) duct which develops in both sexes under the influence of the Wolffian (mesonephric) duct. For a better understanding of the interactions between the Müllerian duct and its adjacent tissues, we present a systematic scanning and transmission electron microscopic investigation of early stages of avian Müllerian duct development. This starts within the cranial part of the Müllerian ridge from a placode-like thickening and deepening of the coelomic epithelium containing nephrostomes as remnants of the last pronephric and first mesonephric tubules. Groups of cells detach from this placode and rapidly expand caudally as a solid cord. This becomes canalized, but the tip region remains mesenchymal and is found enclosed within the basal lamina of the Wolffian duct. Immunostaining reveals that the Müllerian duct migrates within a matrix rich in laminin and entactin. When the canalized duct has opened into the coelomic cavity, one or more secondary ducts are found immediately caudal of the main funnel, for a short period only, possibly to supply material to the expanding duct. BrdU-anti-BrdU reaction reveals a high proliferation of the duct epithelium. The thickened epithelium of the Müllerian ridge dissolves to form the mesenchymal layers of the duct. Immunostaining with vimentin argues against a cellular contribution of Wolffian duct cells to the Müllerian duct. Comparing the data from avian embryos with those of human indicates that the modalities of early Müllerian duct development are similar in both species.

Blood pressure and the susceptibility to renal damage after unilateral nephrectomy and L-NAME-induced hypertension in rats

BACKGROUND

Fawn-hooded hypertensive (FHH) rats carry several genes which determine the susceptibility to develop renal damage, while renal damage resistant August x Copenhagen Irish (ACI) rats do not. Kidneys from heterozygous (FHH x ACI) F(1) rats, appear to be largely, but not completely, protected after blood pressure elevation with N(omega)-nitro-L-arginine methyl ester (L-NAME). We examined the role of an increased haemodynamic burden on the development of renal damage combining unilateral nephrectomy (UNx)- and L-NAME-induced hypertension in F(1) and ACI rats. Additionally, we investigated whether a general toxic effect of L-NAME, independent from a blood pressure elevation, caused renal damage in F(1) rats in animals simultaneously treated with L-NAME and the ACE inhibitor lisinopril.

METHODS

Surgery was performed and L-NAME treatment (50 or 150 mg/l) was started at the age of 15 weeks. Systolic blood pressure (SBP) and urinary albumin excretion (UaV) were measured at 6 and 12 weeks post-UNx, followed by autopsy to determine the incidence of focal glomerulosclerosis (FGS). Using lisinopril (LIS) and L-NAME, another group of rats was evaluated at 12, 18, and 24 weeks after start of treatment.

RESULTS

At similar L-NAME intake, F, rats developed more severe hypertension and more UaV than ACI rats. The increase in UaV per mmHg increase in SBP was fivefold higher in F(1) compared with ACI rats. In F(1) rats, the increase in UaV per percentage incidence increase in FGS was three times higher. In LIS treated F(1) rats, no significant UaV or FGS was measured at low blood pressure levels, indicating that renal damage in hypertensive F(1) rats is not a direct effect of L-NAME, but the result of the high blood pressure or another action of the renin-angiotensin system.

CONCLUSION

We conclude that heterozygosity for the genes influencing the development of renal damage in the FHH strain increases the susceptibility of the kidney to develop damage after UNx combined with systemic hypertension.

Lack of association between a biallelic polymorphism in the adducin gene and blood pressure in whites and African Americans

Population-based candidate gene association analyses are becoming increasingly popular as a result of a greater number of genes and gene polymorphisms having been identified for which some functional information is available. Because many biochemical and physiologic systems impact blood pressure regulation and hypertension susceptibility, many of these identified genes and polymorphisms are candidates for population-level association studies involving blood pressure levels or hypertension status. Recent studies have suggested that the alpha-adducin gene may harbor polymorphisms that influence blood pressure level. Therefore, we embarked on a study to test one such polymorphism in two large US samples: one from an urban African American population (Maywood, IL) and another from a rural white population (Tecumseh, MI). We used both family-based association tests and tests that consider the impact of additional measured factors beyond adducin gene variation on blood pressure levels. We found no evidence for a significant effect of the chosen adducin polymorphism on blood pressure variation in either sample. We also found no association between Adducin genotypes and antihypertensive use. These facts, together with similar findings in companion studies, suggest that the alpha-adducin gene polymorphism does not have a pronounced effect on blood pressure variation in the populations studied. This does not suggest, however, that the alpha-adducin gene does not have a role in blood pressure regulation and hypertension susceptibility.

Genetically defined risk of salt sensitivity in an intercross of Brown Norway and Dahl S rats

A genetic segregation analysis was performed to identify genes that cosegregate with arterial blood pressure traits reflective of salt sensitivity. A population of 113 F2 male rats was derived from an intercross of inbred SS/JrHsd/Mcw (Dahl salt-sensitive) and BN/SsN/Mcw (Brown Norway) rats. Rats were maintained on an 8% salt diet from the age of 9 to 13 wk, and arterial pressure was measured for 3 h daily during the 4th wk of high salt intake in unanesthetized rats using implanted arterial catheters. At the end of the 3rd day of high-salt pressure recordings, the arterial pressure response to salt depletion was determined 1.5 days following treatment with Lasix and a low-sodium (0. 4%) diet. A genome-wide scan using 265 polymorphic simple sequence length polymorphism (SSLP) markers found that seven arterial pressure phenotypes determined at different times and circumstances, and representing two distinct indexes of salt sensitivity, mapped to the same region of rat chromosome 18. The trait of salt sensitivity was strongly influenced by the presence of SS alleles in this region of chromosome 18, and those rats which were homozygote SS/SS exhibited a significantly greater reduction of mean arterial pressure following sodium depletion (29 +/- 2 mmHg) than homozygote BN/BN (17 +/- 3 mmHg) or heterozygotic (22 +/- 2 mmHg) rats. This region of rat chromosome 18 corresponds to the long arm of human chromosome 5 and a region of human chromosome 18 that has been linked to hypertension in humans. Given the unlikely chance of these different blood pressure traits mapping to the same region, we believe these data provide evidence that this region of rat chromosome 18 plays an important role in salt-induced hypertension.

New target regions for human hypertension via comparative genomics

Models of human disease have long been used to understand the basic pathophysiology of disease and to facilitate the discovery of new therapeutics. However, as long as models have been used there have been debates about the utility of these models and their ability to mimic clinical disease at the phenotypic level. The application of genetic studies to both humans and model systems allows for a new paradigm, whereby a novel comparative genomics strategy combined with phenotypic correlates can be used to bridge between clinical relevance and model utility. This study presents a comparative genomic map for "candidate hypertension loci in humans" based on translating QTLs between rat and human, predicting 26 chromosomal regions in the human genome that are very likely to harbor hypertension genes. The predictive power appears robust, as several of these regions have also been implicated in mouse, suggesting that these regions represent primary targets for the development of SNPs for linkage disequilibrium testing in humans and/or provide a means to select specific models for additional functional studies and the development of new therapeutics.

Resistance to myocardial ischemia in five rat strains: is there a genetic component of cardioprotection?

There is a need to develop new and more consistent animal models of cardioprotection. Traditionally, outbred dogs, rabbits, and rats have been studied. We determined resistance to ischemia in isolated hearts from inbred strains of rats. Hearts from inbred rats: SS/Mcw (Dahl S, Dahl salt-sensitive), DA/Hsd (Dark Agouti), LEW/Hsd (Lewis), and BN/SsN/Mcw (Brown Norway); and from an outbred rat: Hsd:WIST (Wistar) were subjected to 27 min of global, no-flow ischemia, followed by 3 h of reperfusion. Infarct size in the Brown Norway rat was 2.5 times less than that observed in the Dahl S rat, with the Dark Agouti, Lewis, and Wistar rats intermediate in response. Hearts from Brown Norway rats were also most resistant to ischemia in terms of postischemic enzyme leakage and contractile and vascular function compared with other strains. The average polymorphism rate between strains revealed that such strains were genetically diverse. This study demonstrates strain differences in resistance to myocardial ischemia, suggesting these rats could be used to study a genetic and/or environmental basis for these differences and to provide new animal models for the physiological study of cardioprotection.

Spontaneous elastic tissue lesions in the rat abdominal aorta, a genetically determined phenotype

In this study, phenotypic expression of spontaneous elastic laminae defects within the rat abdominal aorta was examined. Lesions in Brown Norway (BN) rats were compared with those of New Zealand genetically hypertensive (GH) rats. BN and GH rats were cross-bred to determine the phenotypic expression of these lesions in successive F(1) and F(2) generations. Lesions were assessed by distribution, number and a semiquantitative index of severity. All BN aortae contained numerous elastic tissue defects. In comparison, GH aortae contained only occasional elastic tissue lesions. F(1) aortae contained lesions in numbers similar to those of the parental BN strain; however, F(1) lesions were of significantly greater severity. Within the F(2) generation, a wide range in both lesion numbers and severity indices was observed, with approximately a quarter of animals having lesion numbers analogous to the GH parental strain. In conclusion, this study indicates that the spontaneous elastic tissue lesions observed within BN rats are consistent with an autosomal dominant, possibly single gene, effect. Moreover, epistatic effects, derived from the GH strain, may influence the severity of these lesions. The gene(s) responsible may be important in the development of conditions such as arteriosclerosis and aneurysms in humans.

Gene structure and chromosomal mapping of the rat smooth muscle calponin gene

Smooth muscle cells (SMC) express a battery of lineage-restricted genes whose encoded proteins impart the unique contractile phenotype that characterizes this muscle type. While the encoded function of many SMC-restricted genes has been extensively analyzed, less is known about their position within the genome and the regulatory factors governing their transcription. In this report, we define the gene structure, 5' promoter analysis, and chromosomal mapping of the rat smooth muscle calponin (CnnI) gene. The rat CnnI gene is comprised of seven exons spanning approximately 8 kb of genomic sequence. The intron-exon boundaries of the rat CnnI gene match precisely those in human and mouse. Primer extension and RNase protection assays indicate two major transcription start positions (tsp). Comparative sequence analysis of the 5' promoter region reveals several conserved cis regulatory elements, including a TA-rich element within 30 nt of the tsp that could be a recognition site for TATA-binding protein and two CCAAT boxes. Transient and stable transfection studies support the hypothesis that distal regulatory elements confer SMC-restricted expression of CnnI. Finally, using an F2 intercross, we have mapped the rat CnnI gene to the telomeric end of Chromosome (Chr) 8. These studies provide additional information relating to the control of CnnI gene expression and provide a platform to begin assessing the potential linkage of CnnI to spontaneous and experimental disease phenotypes in rats.

Molecular cloning, tissue-specific expression, and chromosomal localization of a novel nerve growth factor-regulated G-protein- coupled receptor, nrg-1

A novel and differentially expressed gene, named nrg-1, was identified by EST expression profiling and subsequently isolated as a 2.2-kb full-length clone from a rat PC12 cell cDNA library. Sequence analysis reveals that nrg-1 encodes a putative seven transmembrane spanning domain protein with structural features characteristic of receptors belonging to the G-protein-coupled receptor gene superfamily. The 400-amino-acid protein encoded by nrg-1 exhibits a high degree of sequence identity (40-44%) to the Edg receptor family; members include Edg-1, Edg-2, Edg-3, Edg-4, and H218. Both Northern analysis andEST expression profiling revealed that whole-tissue distribution of nrg-1 mRNA is restricted, found almost exclusively in brain. Transcripts of nrg-1 could be ubiquitously detected in different regions, with very prominent expression in lower brain regions such as the midbrain, pons,medulla, and spinal cord. In PC12 cells, nerve growth factor induces neuronal differentiation and repressed expression of nrg-1. Two other agents that differentiate PC12 cells, fibroblast growth factor and dibdutyryl cAMP, down-regulated nrg-1 mRNA levels. Epidermal growth factor, and agent that does not induce differentiation, did not repress nrg-1 mRNA levels. In a PC12 cell mutant that is deficient in protein kinase A activity (AB.11), all three differentiating agents were unable to down-regulate nrg-1 mRNA. Hence, protein kinase A appears to be an obligatory cellular component in nrg-1 mRNA regulation. Chromosomal mapping employing a rat somatic cell readiation hybrid panel demonstrated that nrg-1 is linked to marker D8Rat54 and tightly associated with H218 on chromosome 8.

Physiological genetics: application to hypertension research

1. The rapid advancement of the human genome within the next 5-7 years begins a new era for biological research. The structure of all approximately 100,000 genes will be known, but the function of the majority of these genes will remain unknown. This paper outlines a 'physiological genetics' strategy for determining the genetic basis of hypertension by combining a variety of techniques (e.g. genetics, molecular biology, bioinformatics and physiology), to help identify gene function and the pathways involved in the development of hypertension in the rat. 2. Using comparative gene mapping, these regions can be used to implicate susceptibility loci for hypertension in humans, resulting in rapid conversion of basic research in animal models to relevant clinical assessment. The present study outlines some new strategies (i.e. whole-animal physiological genetics) as a means to study disease aetiology in polygenic disorders and to facilitate gene identification in the ascent of functional genomics.

A high-density integrated genetic linkage and radiation hybrid map of the laboratory rat

The laboratory rat (Rattus norvegicus) is a key animal model for biomedical research. However, the genetic infrastructure required for connecting phenotype and genotype in the rat is currently incomplete. Here, we report the construction and integration of two genomic maps: a dense genetic linkage map of the rat and the first radiation hybrid (RH) map of the rat. The genetic map was constructed in two F2 intercrosses (SHRSP x BN and FHH x ACI), containing a total of 4736 simple sequence length polymorphism (SSLP) markers. Allele sizes for 4328 of the genetic markers were characterized in 48 of the most commonly used inbred strains. The RH map is a lod >/= 3 framework map, including 983 SSLPs, thereby allowing integration with markers on various genetic maps and with markers mapped on the RH panel. Together, the maps provide an integrated reference to >3000 genes and ESTs and >8500 genetic markers (5211 of our SSLPs and >3500 SSLPs developed by other groups). [Bihoreau et al. (1997); James and Tanigami, RHdb (http:www.ebi.ac.uk/RHdb/index.html); Wilder (http://www.nih.gov/niams/scientific/ratgbase); Serikawa et al. (1992); RATMAP server (http://ratmap.gen.gu.se)] RH maps (v. 2.0) have been posted on our web sites at http://goliath.ifrc.mcw.edu/LGR/index.html or http://curatools.curagen.com/ratmap. Both web sites provide an RH mapping server where investigators can localize their own RH vectors relative to this map. The raw data have been deposited in the RHdb database. Taken together, these maps provide the basic tools for rat genomics. The RH map provides the means to rapidly localize genetic markers, genes, and ESTs within the rat genome. These maps provide the basic tools for rat genomics. They will facilitate studies of multifactorial disease and functional genomics, allow construction of physical maps, and provide a scaffold for both directed and large-scale sequencing efforts and comparative genomics in this important experimental organism.

Altered renal hemodynamics and impaired myogenic responses in the fawn-hooded rat

The present study examined whether an abnormality in the myogenic response of renal arterioles that impairs autoregulation of renal blood flow (RBF) and glomerular capillary pressure (PGC) contributes to the development of renal damage in fawn-hooded hypertensive (FHH) rats. Autoregulation of whole kidney, cortical, and medullary blood flow and PGC were compared in young (12 wk old) FHH and fawn-hooded low blood pressure (FHL) rats in volume-replete and volume-expanded conditions. Baseline RBF, cortical and medullary blood flow, and PGC were significantly greater in FHH than in FHL rats. Autoregulation of renal and cortical blood flow was significantly impaired in FHH rats compared with results obtained in FHL rats. Myogenically mediated autoregulation of PGC was significantly greater in FHL than in FHH rats. PGC rose from 46 +/- 1 to 71 +/- 2 mmHg in response to an increase in renal perfusion pressure from 100 to 150 mmHg in FHH rats, whereas it only increased from 39 +/- 2 to 53 +/- 1 mmHg in FHL rats. Isolated perfused renal interlobular arteries from FHL rats constricted by 10% in response to elevations in transmural pressure from 70 to 120 mmHg. In contrast, the diameter of vessels from FHH rats increased by 15%. These results indicate that the myogenic response of small renal arteries is altered in FHH rats, and this contributes to an impaired autoregulation of renal blood flow and elevations in PGC in this strain.

Mapping and characterization of quantitative trait loci for non-insulin-dependent diabetes mellitus with an improved genetic map in the Otsuka Long-Evans Tokushima fatty rat

The Otsuka Long-Evans Tokushima Fatty (OLETF) rat is an animal model for obese-type, non-insulin-dependent diabetes mellitus (NIDDM) in humans. We have previously reported four quantitative trait loci (QTLs) responsible for NIDDM on Chromosomes (Chrs) 7, 14, 8, and 11 (Nidd1-4/of for Non-insulin-dependent diabetes1-4/oletf) by a whole-genome search in 160 F2 progenies obtained by mating the OLETF and the Fischer-344 (F344) rats. Our present investigation was designed to identify and characterize novel QTLs affecting NIDDM by performing a genome-wide linkage analysis of genes for glucose levels and body weight and analysis for gene-to-gene and gene-to-body-weight interactions on an improved genetic map with a set of 382 informative markers in the 160 F2 progenies. We have identified seven novel QTLs on rat Chrs 1 (Nidd5 and 6/of), 5 (Nidd7/of), 9 (Nidd8/of), 12 (Nidd9/of), 14 (Nidd10/of) and 16 (Nidd11/of) which, together with the Nidd1-4/of, account for a total of approximately 60% and approximately 75% of the genetic variance of the fasting and postprandial glucose levels, respectively, in the F2. While the OLETF allele corresponds with increased glucose levels as expected for the novel QTLs except Nidd8 and 9/of, the Nidd8 and 9/of exhibit heterosis: heterozygotes showing significantly higher glucose levels than OLETF or F344 homozygotes. There are epistatic interactions between Nidd1 and 10/of and between Nidd2 and 8/of. Additionally, our results indicated that the Nidd6 and 11/of could also contribute to an increase of body weight, and that the other five QTLs could show no linkage with body weight, but Nidd8,9, and 10/of have an interaction with body weight.

Impaired autoregulation of renal blood flow in the fawn-hooded rat

The responses to changes in renal perfusion pressure (RPP) were compared in 12-wk-old fawn-hooded hypertensive (FHH), fawn-hooded low blood pressure (FHL), and August Copenhagen Irish (ACI) rats to determine whether autoregulation of renal blood flow (RBF) is altered in the FHH rat. Mean arterial pressure was significantly higher in conscious, chronically instrumented FHH rats than in FHL rats (121 +/- 4 vs. 109 +/- 6 mmHg). Baseline arterial pressures measured in ketamine-Inactin-anesthetized rats averaged 147 +/- 2 mmHg (n = 9) in FHH, 132 +/- 2 mmHg (n = 10) in FHL, and 123 +/- 4 mmHg (n = 9) in ACI rats. Baseline RBF was significantly higher in FHH than in FHL and ACI rats and averaged 9.6 +/- 0.7, 7.4 +/- 0.5, and 7.8 +/- 0.9 ml. min-1. g kidney wt-1, respectively. RBF was autoregulated in ACI and FHL but not in FHH rats. Autoregulatory indexes in the range of RPPs from 100 to 150 mmHg averaged 0.96 +/- 0.12 in FHH vs. 0.42 +/- 0.04 in FHL and 0.30 +/- 0.02 in ACI rats. Glomerular filtration rate was 20-30% higher in FHH than in FHL and ACI rats. Elevations in RPP from 100 to 150 mmHg increased urinary protein excretion in FHH rats from 27 +/- 2 to 87 +/- 3 microg/min, whereas it was not significantly altered in FHL or ACI rats. The percentage of glomeruli exhibiting histological evidence of injury was not significantly different in the three strains of rats. These results indicate that autoregulation of RBF is impaired in FHH rats before the development of glomerulosclerosis and suggest that an abnormality in the control of renal vascular resistance may contribute to the development of proteinuria and renal failure in this strain of rats.

Identification of quantitative trait loci for non-insulin-dependent diabetes mellitus that interact with body weight in the Otsuka Long-Evans Tokushima Fatty rat

Non-insulin-dependent diabetes mellitus (NIDDM) is a prototypical multifactorial disease. Genetic predisposition and obesity are major risk factors for NIDDM development and the interactions between these factors are likely to be important in the etiology of this disease. The Otsuka Long-Evans Tokushima Fatty (OLETF) rat is one of the best animal models of NIDDM, since the OLETF rat develops NIDDM with mild obesity that is very similar to human NIDDM. Therefore, the OLETF rat is a powerful model for investigating the interaction between genetic susceptibility to NIDDM and obesity. In this study, our goal was to clarify the relationship between an individual NIDDM susceptibility locus and obesity in the OLETF using a molecular genetics approach. We identified four novel quantitative trait loci (QTLs) that contribute to the susceptibility to NIDDM, none of which shows significant linkage with body weight. However, Nidd1/of on chromosome 7 and Nidd2/of on chromosome 14 have an interaction with body weight. In contrast, one locus was mapped to chromosome 10 for body weight, but not to fasting or postprandial glucose levels. These data illustrate that NIDDM and body weight are under separate genetic control in the OLETF yet interact to yield the final disease phenotype in the two Nidd/of loci. In addition, body weight could be used in place of body mass index as an indicator of obesity in our experimental system of genetic study. This study will facilitate the understanding of the complex interaction between genetic susceptibility to NIDDM and obesity.

Gene-based anchoring of the rat genetic linkage and cytogenetic maps: new regional localizations, orientation of the linkage groups, and insights into mammalian chromosome evolution

In order to generate anchor points connecting the rat cytogenetic and genetic maps, the cytogenetic position of 62 rat markers (including 55 genes) already localized genetically was determined by fluorescence in situ hybridization. Whenever possible, markers located near one end of the linkage groups were included. These new localizations allowed us to unambiguously orient the 20 autosomal and the X chromosome linkage groups. The position of the centromere in the linkage map could also be determined in the case of several metacentric chromosomes. In addition, the regional localization of 15 other rat genes was determined. These new data bring useful information with respect to comparative mapping with the mouse and the human and to mammalian evolution. They illustrate, for instance, that groups of genes can remain syntenic during mammalian evolution while being subjected to intrachromosomal rearrangements in some lineages (synteny is conserved while gene order is not). This analysis also disclosed cases of synteny conservation in one the two rodent species and the human, while the synteny is split in the other rodent species: such configurations are likely examples of lineage-specific interchromosomal rearrangements associated with speciation.

An integrated genetic linkage map of the laboratory rat

The laboratory rat, Rattus novegicus, is a major model system for physiological and pathophysiological studies, and since 1966 more than 422,000 publications describe biological studies on the rat (NCBI/Medline). The rat is becoming an increasingly important genetic model for the study of specific diseases, as well as retaining its role as a major preclinical model system for pharmaceutical development. The initial genetic linkage map of the rat contained 432 genetic markers (Jacob et al. 1995) out of 1171 developed due to the relatively low polymorphism rate of the mapping cross used (SHR x BN) when compared to the interspecific crosses in the mouse. While the rat genome project continues to localize additional markers on the linkage map, and as of 11/97 more than 3,200 loci have been mapped. Current map construction is using two different crosses (SHRSP x BN and FHH x ACI) rather than the initial mapping cross. Consequently there is a need to provide integration among the different maps. We set out to develop an integrated map, as well as increase the number of markers on the rat genetic map. The crosses available for this analysis included the original mapping cross SHR x BN reciprocal F2 intercross (448 markers), a GH x BN intercross (205 markers), a SS/Mcw x BN intercross (235 markers), and a FHH/Eur x ACI/Hsd intercross (276 markers), which is also one of the new mapping crosses. Forty-six animals from each cross were genotyped with markers polymorphic for that cross. The maps appear to cover the vast majority of the rat genome. The availability of these additional markers should facilitate more complete whole genome scans in a greater number of strains and provide additional markers in specific genomic regions of interest.

A microsatellite genetic linkage map for zebrafish (Danio rerio)

We have constructed a zebrafish genetic linkage map consisting of 705 simple sequence-length polymorphism markers (SSLPs). The map covers 2350 centimorgans (cM) of the zebrafish genome with an average resolution of 3.3 cM. It is a complete map in genetic mapping terms (there is one linkage group for each of the 25 chromosomes), and it has been confirmed by somatic-cell hybrids and centromere-mapping using half-tetrad analysis. The markers are highly polymorphic in the zebrafish strains used for genetic crosses and provide a means to compare genetic segregation of developmental mutations between laboratories. These markers will provide an initial infrastructure for the positional cloning of the nearly 600 zebrafish genes identified as crucial to vertebrate development,and will become the anchor for the physical map of the zebrafish genome.