Lines Of Laboratory Mice Research Articles

Metabolic Rate and Oxidative Stress as a Risk Factors in the Development of Colorectal Cancer.

There is growing evidence that the body's energy expenditures constitute a significant risk factor for the development of most deadly diseases, including cancer. Our aim was to investigate the impact of basal metabolic rate (BMR) on the growth and progression of colorectal cancer (CRC). To do so, we used a unique model consisting of three lines of laboratory mice (Mus musculus) artificially selected for high (HBMR) and low (LBMR) basal metabolic rate and randomly bred individuals (non-selected, NSBMR). The experimental individuals were implanted with human colorectal cancer cells DLD-1. The variation in BMR between the lines allowed for testing the impact of whole-body metabolism on oxidative and antioxidant parameters in the liver throughout the cancerogenesis process. We investigated the dependence between metabolic values, reactive oxygen species (ROS) levels, and Kelch-like ECH-associated protein 1-based E3 ligase complexes (Keap1) gene activity in these animals. We found that the HBMR strain had a higher concentration of oxidative enzymes compared to the LBMR and NSBMR. Furthermore, the growth rate of CRC tumors was associated with alterations in the levels of oxidative stress enzymes and Keap1 expression in animals with a high metabolic rate. Our results indicate that a faster growth and development of CRC line DLD-1 is associated with enzymatic redox imbalance in animals with a high BMR.

Tuberculosis susceptibility in genetically diverse mice reveals functional diversity of neutrophils.

Tuberculosis (TB) is a heterogenous disease in humans with individuals exhibiting a wide range of susceptibility. This heterogeneity is not captured by standard laboratory mouse lines. We used a new collection of 19 wild-derived inbred mouse lines collected from diverse geographic sites to identify novel phenotypes during Mycobacterium tuberculosis ( Mtb ) infection. Wild derived mice have heterogenous immune responses to infection that result in differential ability to control disease at early timepoints. Correlation analysis with multiple parameters including sex, weight, and cellular immune responses in the lungs revealed that enhanced control of infection is associated with increased numbers of CD4 T cells, CD8 T cells and B cells. Surprisingly, we did not observe strong correlations between IFN-γ production and control of infection. Although in most lines high neutrophils were associated with susceptibility, we identified a mouse line that harbors high neutrophils numbers yet controls infection. Using single-cell RNA sequencing, we identified a novel neutrophil signature associated with failure to control infection.

Principles of Creation of a Genetic Engineering Construction for Obtaining Humanized Transgenic Mice with <i>HLA-C*07:02:01:01</i>, as a Promote of Innovative Transgenic and Knockout Biomodels

Genetic differences in different populations influence the mechanism and efficacy of drugs. Biomodels that take into account the peculiarities of genetic polymorphism in different individuals allow to more fully investigate the molecular-genetic mechanisms of action of pharmacological agents, including immunobiological ones. Recombinant DNA encoding a hybrid MHC class I protein containing human ß2-microglobulin fused with antigen-presenting domains (α1 and α2 domains) of the HLA-C*07:02:01:01 molecule and α3 domain of the mouse H2-complex was created. The purified linearized DNA fragment containing the target construct flanked by regulatory fragments ensuring its stable transcription was used to obtain a new line of humanized transgenic mice. The principles of designing humanized transgenic mice by encoding a chimeric MHC class I protein containing antigen-presenting domains HLA-C*07:02:01:01 are similar to those for obtaining mice of the HLA-А*02:01:01 and HLA-B*18:01:01:02 humanized transgenic lines. These transgenic lines of laboratory mice are independent biomodels, and also be used as baselines for obtaining corresponding transgenic and knockout lines.

Digestibility of crude nutrients and minerals in C57Bl/6J and CD1 mice fed a pelleted lab rodent diet

In laboratory animals, there is a scarcity of digestibility data under non-experimental conditions. Such data is important as basis to generate nutrient requirements, which contributes to the refinement of husbandry conditions. Digestibility trials can also help to identify patterns of absorption and potential factors that influence the digestibility. Thus, a digestibility trial with a pelleted diet used as standard feed in laboratory mice was conducted. To identify potential differences between genetic lines, inbred C57Bl/6 J and outbred CD1 mice (n = 18 each, male, 8 weeks-old, housed in groups of three) were used. For seven days, the feed intake was recorded and the total faeces per cage collected. Energy, crude nutrient and mineral content of diet and faecal samples were analyzed to calculate the apparent digestibility (aD). Apparent dry matter and energy digestibility did not differ between both lines investigated. The C57Bl/6 J mice had significantly higher aD of magnesium and potassium and a trend towards a lower aD of sodium than the mice of the CD1 outbred stock. Lucas-tests were performed to calculate the mean true digestibility of the nutrients and revealed a uniformity of the linear regression over data from both common laboratory mouse lines. The mean true digestibility of crude nutrients was > 90%, except for fibre, that of the minerals ranged between 66 and 97%.

Mice selected for a high basal metabolic rate evolved larger guts but not more efficient mitochondria.

Intra-specific variation in both the basal metabolic rate (BMR) and mitochondrial efficiency (the amount of ATP produced per unit of oxygen consumed) has profound evolutionary and ecological consequences. However, the functional mechanisms responsible for this variation are not fully understood. Mitochondrial efficiency is negatively correlated with BMR at the interspecific level but it is positively correlated with performance capacity at the intra-specific level. This discrepancy is surprising, as theories explaining the evolution of endothermy assume a positive correlation between BMR and performance capacity. Here, we quantified mitochondrial oxidative phosphorylation activity and efficiency in two lines of laboratory mice divergently selected for either high (H-BMR) or low (L-BMR) levels of BMR. H-BMR mice had larger livers and kidneys (organs that are important predictors of BMR). H-BMR mice also showed higher oxidative phosphorylation activity in liver mitochondria but this difference can be hypothesized to be a direct effect of selection only if the heritability of this trait is low. However, mitochondrial efficiency in all studied organs did not differ between the two lines. We conclude that the rapid evolution of BMR can reflect changes in organ size rather than mitochondrial properties, and does not need to be accompanied obligatorily by changes in mitochondrial efficiency.

Variations in microbiota composition of laboratory mice influence Citrobacter rodentium infection via variable short-chain fatty acid production.

The composition of the intestinal microbiota influences the outcome of enteric infections in human and mice. However, the role of specific members and their metabolites contributing to disease severity is largely unknown. Using isogenic mouse lines harboring distinct microbiota communities, we observed highly variable disease kinetics of enteric Citrobacter rodentium colonization after infection. Transfer of communities from susceptible and resistant mice into germ-free mice verified that the varying susceptibilities are determined by microbiota composition. The strongest differences in colonization were observed in the cecum and could be maintained in vitro by coculturing cecal bacteria with C. rodentium. Cohousing of animals as well as the transfer of cultivable bacteria from resistant to susceptible mice led to variable outcomes in the recipient mice. Microbiome analysis revealed that a higher abundance of butyrate-producing bacteria was associated with the resistant phenotype. Quantification of short-chain fatty acid (SCFA) levels before and after infection revealed increased concentrations of acetate, butyrate and propionate in mice with delayed colonization. Addition of physiological concentrations of butyrate, but not of acetate and/or propionate strongly impaired growth of C. rodentium in vitro. In vivo supplementation of susceptible, antibiotic-treated and germ-free mice with butyrate led to the same level of protection, notably only when cecal butyrate concentration reached a concentration higher than 50 nmol/mg indicating a critical threshold for protection. In the recent years, commensal-derived primary and secondary bacterial metabolites emerged as potent modulators of hosts susceptibility to infection. Our results provide evidence that variations in SCFA production in mice fed fibre-rich chow-based diets modulate susceptibility to colonization with Enterobacteriaceae not only in antibiotic-disturbed ecosystems but even in undisturbed microbial communities. These findings emphasise the need for microbiota normalization across laboratory mouse lines for infection experiments with the model-pathogen C. rodentium independent of investigations of diet and antibiotic usage.

A novel polymorphism in the fatty acid desaturase 2 gene (Fads2): A possible role in the basal metabolic rate.

Fatty acyl composition of cell membrane lipids, particularly the abundance of highly unsaturated docosahexaenoic fatty acid (22:6n-3, DHA), is likely to be an important predictor of basal metabolic rate (BMR). Our study was performed using two lines of laboratory mice divergently selected for either high or low BMR. We describe a novel single nucleotide polymorphism in the Fads2 gene encoding Δ6-desaturase, a key enzyme in the metabolic pathways of polyunsaturated fatty acids (PUFAs). The allele frequencies of Fads2 were significantly different in both lines of mice. The analysis of genetic distances revealed that the genetic differentiation between the two studied lines developed significantly faster at the Fads2 locus than it did at neutral loci. Such a pattern suggests that the Fads2 polymorphism is related to the variation in BMR, i.e. the direct target of selection. The Fads2 polymorphism significantly affected abundance of several PUFAs; however, the differences in PUFA composition between lines were compatible with the difference in frequency of Fads2 alleles only for DHA. We hypothesize that the polymorphism in the Fads2 gene affects the BMR through modification of DHA abundance in cell membranes. This may be the first example of a significant link between a polymorphism in a gene responsible for fatty acyl composition and variation in BMR.

Genetically modified laboratory mice with sebaceous glands abnormalities.

Sebaceous glands (SG) are exocrine glands that release their product by holocrine secretion, meaning that the whole cell becomes a secretion following disruption of the membrane. SG may be found in association with a hair follicle, forming the pilosebaceous unit, or as modified SG at different body sites such as the eyelids (Meibomian glands) or the preputial glands. Depending on their location, SG fulfill a number of functions, including protection of the skin and fur, thermoregulation, formation of the tear lipid film, and pheromone-based communication. Accordingly, SG abnormalities are associated with several diseases such as acne, cicatricial alopecia, and dry eye disease. An increasing number of genetically modified laboratory mouse lines develop SG abnormalities, and their study may provide important clues regarding the molecular pathways regulating SG development, physiology, and pathology. Here, we summarize in tabulated form the available mouse lines with SG abnormalities and, focusing on selected examples, discuss the insights they provide into SG biology and pathology. We hope this survey will become a helpful information source for researchers with a primary interest in SG but also as for researchers from unrelated fields that are unexpectedly confronted with a SG phenotype in newly generated mouse lines.

Construction and investigation of 3D vessels net of the brain according to MRI data using the method of variation of scanning plane

The blood realizes the transport of substances, which are necessary for livelihoods, throughout the body. The assumption about the relationship genotype and structure of vasculature (in particular of brain) is natural. In the paper we consider models of vessel net for two genetic lines of laboratory mice. Vascular net obtained as a result of preprocessing MRI data. MRI scanning is realized using the method of variation of slope of scanning plane, i.e. by several sets of parallel planes specified by different normal vectors. The following special processing allowed to construct models of vessel nets without fragmentation. The purpose of the work is to compare the vascular network models of two different genetic lines of laboratory mice.

Variation in sexual dimorphism of mouse os coxae shape, volume, and bone mineral density in response to selection for high voluntary wheel running

Pelvic (os coxae and sacrum) dimorphism is common in mammals. Studies (primarily on human and non‐human primates) of pelvic dimorphism suggest that dimorphism results from an evolutionary trade‐off between reproduction and locomotion. Previous work has shown that pelvic morphology varies in relation to locomotor modes among species and that, along with other girdle elements such as the scapula, high levels of voluntary activity cause training responses in mice. We analyzed three lines of laboratory mice, from an ongoing selection experiment, two of which have been bred for 59 generations for high levels of voluntary wheel running (HR) and one that is a non‐selected control (C) line. One selected line (HRMINI) is fixed for a “mighty mini‐muscle” mutation that reduces skeletal muscle mass by up to 50%. The other selected line (HRNORMAL) does not possess this mutation.We used two dimensional geometric morphometric techniques to produce quantitative descriptors of os coxae shape (Relative Warp scores) and geometric (centroid) size. In addition, we used X‐ray micro computed tomography (μCT) to measure elements of bone microstructure (bone mineral density (BMD) and bone volume (BV)).ANOVAs showed significant differences in body size (length and mass) among the lines and between the sexes. Both HR lines were smaller than the C line, and the HRMINI line was smaller than the HRNORMAL line. However, although females were smaller than males in all three lines, os coxae centroid size was greater in females. Finally, for all size metrics, no significant sex‐by‐line interaction was present, indicating no differential sexual dimorphism among lines.Analyses of μCT data, with body size as a covariate, showed significant differences in BMD and BV of the os coxae among lines and between sexes. Females had higher BMD and BV than males, and HR lines had lower values than the C line (the HRMINI line showed the largest decrease). Additionally, a significant sex‐by‐line interaction in the analysis of BMD suggests a stronger effect of selection on males than on females.Finally, MANCOVAs, with body size as a covariate, revealed significant shape differences among lines and between sexes. A significant sex‐by‐line interaction was also found, indicating different patterns of shape difference between males and females, depending on line.These results indicate that although there is no effect of selective breeding or the mini‐muscle mutation on patterns of sexual dimorphism in body and os coxae size, this is not the case for patterns of sexual dimorphism in other components of coxal morphology. Male and female differences in os coxae shape and bone microstructure have different trajectories and magnitudes depending on line, suggesting that in some cases, males and females respond to selection and the mini‐muscle mutation in different ways.Support or Funding InformationMJ Murdock Charitable Trust to HS, KB & CHU.C. Riverside Chancellor's Postdoctoral Fellowship to HSNSF IOS‐1121273 to TG

Nonshivering thermogenesis capacity versus basal metabolic rate in laboratory mice

I wanted to follow the correlation between level of basal metabolic rate (BMR) and maximum response to injection of noradrenaline (MMR NA) in two lines of laboratory mice subjected to divergent, artificial selection toward high BMR (HBMR) and low BMR (LBMR). HBMR animals had heavier visceral organs (heart, liver, kidney, intestine), but their regulatory NST (MMR NA–BMR) was lower and interscapular brown adipose tissue (IBAT) lighter than in LBMR mice. Obligatory part of nonshivering thermogenesis (NST) (in other words BMR) depended on visceral organ mass, whereas regulatory NST correlates with mass of IBAT. BMR was not correlated with total NST capacity, but phenotypic correlation between obligatory and regulatory NST was negative. This suggests possibility of substitution of obligatory NST to thermoregulation in a place of the regulatory NST. Then total thermoregulatory energy expenditures do not change.

Effects of Size, Sex, and Voluntary Running Speeds on Costs of Locomotion in Lines of Laboratory Mice Selectively Bred for High Wheel‐Running Activity

Selective breeding for over 35 generations has led to four replicate (S) lines of laboratory house mice (Mus domesticus) that run voluntarily on wheels about 170% more than four random-bred control (C) lines. We tested whether S lines have evolved higher running performance by increasing running economy (i.e., decreasing energy spent per unit of distance) as a correlated response to selection, using a recently developed method that allows for nearly continuous measurements of oxygen consumption (VO2) and running speed in freely behaving animals. We estimated slope (incremental cost of transport [COT]) and intercept for regressions of power (the dependent variable, VO2/min) on speed for 49 males and 47 females, as well as their maximum VO2 and speeds during wheel running, under conditions mimicking those that these lines face during the selection protocol. For comparison, we also measured COT and maximum aerobic capacity (VO2max) during forced exercise on a motorized treadmill. As in previous studies, the increased wheel running of S lines was mainly attributable to increased average speed, with males also showing a tendency for increased time spent running. On a whole-animal basis, combined analysis of males and females indicated that COT during voluntary wheel running was significantly lower in the S lines (one-tailed P=0.015). However, mice from S lines are significantly smaller and attain higher maximum speeds on the wheels; with either body mass or maximum speed (or both) entered as a covariate, the statistical significance of the difference in COT is lost (one-tailed P> or =0.2). Thus, both body size and behavior are key components of the reduction in COT. Several statistically significant sex differences were observed, including lower COT and higher resting metabolic rate in females. In addition, maximum voluntary running speeds were negatively correlated with COT in females but not in males. Moreover, males (but not females) from the S lines exhibited significantly higher treadmill VO2max as compared to those from C lines. The sex-specific responses to selection may in part be consequences of sex differences in body mass and running style. Our results highlight how differences in size and running speed can account for lower COT in S lines and suggest that lower COT may have coadapted in response to selection for higher running distances in these lines.

Circadian rhythm of core body temperature in two laboratory mouse lines

The circadian rhythm of core body temperature (Tb) was examined in two mouse lines bidirectionally selected for nest-building behavior (small (SNB) and big nest-builders (BNB)). This selection also resulted in more robust circadian organization of wheel-running activity in the SNB compared to the BNB mice. Tb was measured by an e-mitter implanted in the abdominal cavity. The circadian Tb rhythm of the SNB was more robust compared to the BNB regardless of whether the animals had access to a running wheel or not and regardless of the lighting conditions, i.e., 12 h : 12 h light : dark (LD) cycle or constant dark (DD). Wheel-running activity rhythms of SNB were more robust in LD and DD compared to BNB. The amplitude of the circadian Tb rhythm increased significantly in response to wheel access in both mouse lines, but was not significantly different between the BNB and SNB. However, BNB tended to have lower amplitudes of circadian Tb rhythm in the absence of running wheels and a larger increase in the amplitude upon access to a running wheel compared to SNB. No differences were found in LD and DD between the lines in mean Tb and wheel-running activity levels. In addition, no differences between the two mouse lines were found in the free-running period of the Tb or wheel-running activity rhythms in DD. Overall, our findings reveal a more robust circadian phenotype of the SNB compared to the BNB.

Daily variation of thermoregulatory costs in laboratory mice selected for high and low basal metabolic rate

Abstract Most mammals are known to have clear circadian rhythms of body temperature ( T b ) and metabolic rate. Large parts of the rhythms correspond to the oscillation of nonshivering thermogenesis (NST), dependent on visceral organ mass, and, affected by mass of brown adipose tissue (BAT). I tested whether: (1) a different levels of BMR result in respective changes of T b values and the magnitude of daily RMR oscillations both within and below thermoneutrality; (2) the amplitude of daily variation of RMR depends on ambient temperature ( T a ). I studied: (1) daily variation of body temperature at T a of 23 °C, and (2) the rate of resting metabolism (RMR) within and below thermoneutrality at the time of minimum and increasing T b (minimum and maximum NST capacity), in two lines of laboratory mice subjected to divergent, artificial selection toward high (HBMR) and low (LBMR) basal rate of metabolism (BMR). All mice had a clear circadian rhythm of T b with minimum of 36.4±0.2 °C at 7:00 and maximum of 37.8±0.2 °C at 21:00. Their RMR measured below thermoneutrality exhibited significant daily variation, with the maximum between 16:00 and 19:00, when T b was rising. Within thermoneutral zone (TNZ) I found between-line, but not between-time, differences in RMR. All between-line differences in RMR could be explained by the magnitude of BMR. I did not find any between-line differences of RMR value in temperatures below thermoneutrality. The amplitude of daily variation of RMR measured below TNZ depended neither on the T a value nor on level of BMR (or visceral organs).

Biochemical characterisation of blood metabolic substances in mice after long-term selection on growth traits

Abstract. A biochemical characterisation of blood was done in laboratory mouse lines originating from a heterogeneous outbred strain Fzt:DU which were selected for high body weight at 6 weeks of age (DU-6), for high total protein amount in the carcass (DU-6P) and for an index combining body weight and treadmill Performance (DU-6+TP) over 54 generations, respectively. The level of the following enzymes and Substrates were compared to the unselected control group (Fzt:DU): alanine aminotransferase (ALAT), aspartate aminotransferase (ASAT), lactate dehydrogenase (LDH), creatine kinase (CK), y-glutamyl-transpeptidase (GGTP), alkaline Phosphatase (AP), total cholesterol with its components LDL+VLDL- and HDL-cholesterol, triglyceride (Trig.), Creatinine (Crea.), lactate (Lac.) and glucose (Gluc). Concentration of some metabolic substances differed significantly in relation to the specific selection character. It is concluded, that selection indirectly diversified physiological State in the tested long-term selection lines in mice.

Delayed aging in Ames dwarf mice. Relationships to endocrine function and body size.

There is considerable evidence for genetic control of aging and longevity. For example, there are major differences in life span between different breeds of domestic dogs, between different inbred lines of laboratory mice, and between lines of mice developed by selection for various phenotypic traits. Studies in yeast, in a round worm, Caenorhabditis elegans, and in the fruit fly, Drosophila melanogaster, provided a wealth of information on the genetic control of aging, including evidence that mutations at specific loci can produce major alterations in the life span. A new term, longevity assurance genes (LAGs), was coined to describe genes involved in the control of the life span. Evidence for the existence of LAGs in yeast, C. elegans, and Drosophila and the effects of mutations at these loci are described in other chapters in this Volume.

Lack of evidence for bovine Y‐chromosomal variation in beef traits. A Bayesian analysis of Simmental data

IntroductionY‐chromosomal loci are genetically responsible for some male‐specific biological processes. The sex determining region Y (SRY), a protein with DNA‐binding activity, is known as the trigger for sex differentiation in mammals. In humans the SRY is encoded by a single exon located on the short arm of the Y chromosome, close to the pseudoautosomal boundary (S inclair et al. 1990). Moreover, the Y chromosome harbours the male‐specific histocompatibility antigen (reviewed by S impson et al. 1997) and there are at least two regions of the Y chromosome, which have been shown to be essential for normal spermatogenesis in mice (E lliott and C ooke 1997).The sexual dimorphism of aggression in mice has led to a search for its foundation on the Y chromosome. The existence of Y‐chromosomal genetic variation for aggressiveness with genetic factors borne both on the pseudoautosomal (YPAR) and on the nonpseudoautosomal (YNPAR) region of the Y chromosome (S luyter et al. 1996) has been shown. Another example for Y‐induced genetic variation in mice is the testis autosomal trait (occurrence of ovaries or ovotestes in XY animals), which is observed when specific Y chromosomes interact with the autosomal background of certain laboratory mouse lines (E isner et al. 1996). A comparison of the resemblance of different types of relatives indicated a nonzero Y‐chromosomal variance for body weight in mice (B& uuml; nger et al. 1995).In cattle the Y chromosomes of the Bos taurus and Bos indicus subspecies can be morphologically distinguished: its shape is submetacentric in B. taurus and acrocentric in B.indicus. This difference is caused by a pericentric inversion (G oldammer et al. 1997) and has frequently been used to investigate the introgression of zebu genes into B. taurus breeds.The polymorphism of the bovine Y chromosome itself and the results of mouse research both direct the scientific curiosity on the possible contribution of the bovine Y chromosome to quantitative genetic variation in cattle, a question which, to the authors’ knowledge, has not been investigated before. In this paper we first discuss the contribution of autosomal, imprinted, and sex‐linked genes to the resemblance of full and half sibs and then present a Bayesian estimation of a Y‐chromosomal variance component for each of four beef traits in young Simmental bulls using mixed linear and threshold models.

Genetic dissection of X-linked interspecific hybrid placental dysplasia in congenic mouse strains.

Interspecific hybridization in the genus Mus results in male sterility and X-linked placental dysplasia. We have generated several congenic laboratory mouse lines (Mus musculus) in which different parts of the maternal X chromosome were derived from M. spretus. A strict positive correlation between placental weight and length of the M. spretus-derived part of the X chromosome was shown. Detailed analysis was carried out with one congenic strain that retained a M. spretus interval between 12.0 and 30.74 cM. This strain consistently produced hyperplastic placentas that exhibited an average weight increase of 180% over the weight of control placentas. In derived subcongenic strains, however, increased placental weight could no longer be observed. Morphometric analysis of these placentas revealed persistence of abnormal morphology. Fully developed placental hyperplasia could be reconstituted by recombination of proximal and central M. spretus intervals with an intervening M. musculus region. These results may suggest that placental dysplasia of interspecific mouse hybrids is caused by multiple loci clustered on the X chromosome that act synergistically. Alternatively, it is possible that changes in chromatin structure in interspecific hybrids that influence gene expression are dependent on the length of the alien chromosome.

MALIGNANT TRANSFORMATION BY POLYOMA VIRUS.

Since the pioneering work of Rous. most research on tumor viruses has been carried out by oncologists rather than by virologists. However, with the recent rapid development of new knowledge concerning the basic mecha­ nisms involved in cytolytic infections with animal viruses, the attention of virologists has been turned to the same questions in the transformation of normal animal cells to malignant cells by the action of tumor viruses. Yet. even now, the amount of such research is limited chiefly because of a lack of available tumor virus-cell systems which lend themselves to modern molecu­ lar biological techniques. The polyoma virus first isolated and studied by Stewart et al. (1) has been investigated by a number of virologists for two reasons. First, it is a more interesting virus since it has the potential of producing a large variety of tumor types in its natural animal host [Stewart et al. (2)]; and, secondly because it can be studied quantitatively by modern virological methods. Although capable of causing malignant transformation in both in vivo and in vitro systems it nevertheless produces a cytolytic infection under certain conditions, and, therefore, can be quantitated in tissue cultures using the plaque technique [Dulbecco & Freeman (3)]. Furthermore, being able to agglutinate guinea pig red blood cells, it can be quantitated by hemagglutina­ tion and through the hemagglutination inhibition (HI)! test can be specifi­ cally identified with ease [Eddy et al. (4)). Since its natural host is the mouse, the availability of many susceptible inbred lines of laboratory mice make it possible to relate in vitro tissue culture phenomena to tumor production in the intact whole animal. This paper will review and evaluate the more important recent research contributions concerning mechanisms of polyoma virus transformation, the relationships between virus and the cell after transformation, and some of the virus-specific properties of the transformed cells. These items will first be considered for the �n vivo transformation and then for that occurring in in vitro systems.