M. T. Font

RNA-induced immunity against a rat sarcoma.

Se estudió el efecto del ARN proveniente del bazo de ratas inmunizadas a un sarcoma transplantable (Sarcoma E 100) en el crecimiento del mismo. Se inyectó ARN normal y ARN de ratas inmunizadas a dos grupos de animales 5 días antes de la implantación del tumor, tomándose un tercer grupo como testigo normal. Los animales que recibieron el ARN inmune tuvieron tumores más pequeños que los de los dos testigos (p < 0.01), a los 30 días después del injerto. Se formula la hipótesis de que el ARN inmune posee la información (memoria inmunológica) para transformar una respuesta inmunitaria primaria en secundaria.

Morphometric skeletal traits, femoral measurements, and bone mineral deposition in mice with agonistic selection for body conformation

Morphometric skeletal traits, femoral histomorphometry, and bone mineral deposition were investigated in two lines of mice (CBi+ and CBi-) divergently selected for body conformation (CBi+: high body weight, long tail; CBi-: low body weight, short tail) and in the unselected control line CBi. Linear morphometric measurements, absolute and relative skeletal weights, absolute and relative femoral weights, and total biomass sustained per unit of total or tail-less skeletal weight were increased in CBi+ mice in comparison with controls. This greater biomass implies a greater mechanical demand that is satisfied by a heavier skeleton. Looking specifically to the femur, CBi+ mice had heavier bones, both absolute and relative, with a greater diameter and a greater cortical thickness, resulting in a greater cortex/diameter ratio than controls. Although morphometric measurement and absolute skeletal weight were lower in CBi- than in CBi mice, the relative skeleton weight and the biomass sustained per unit of skeletal weight were not modified in the downward selection line when compared with controls. Therefore, CBi- mice did not exhibit a greater mechanical demand as CBi+ mice did. These results led us to consider at least three main aspects: bone length growth; cortical thickness/bone diameter ratio; and bone calcification. The long bones appeared to have a genetically determined predisposition to achieve a given length, which, however, could be modified by artificial selection. Cortical thickness would be directly related to the biomass sustained. This variable increased in CBi+ mice, a genotype that supports a greater biomass than controls, and did not change in CBi- mice, which sustained the same biomass as CBi. The pattern of mineral deposition did not accompany the functional demand because it was higher in CBi- than in CBi+; however, as artificial selection separately affected bone material quality and bone architectural design, these genotypes could express architectural modifications that override any change in bone material quality.

Morphometric traits and femoral histomorphometry in mice selected for body conformation.

Skeleton characteristics and femoral histomorphometry were investigated in two lines of mice divergently selected for antagonistic conformations (CBi/C: high body weight-short tail; CBi/L: low body weight-long tail). An unselected control line (CBi) was used. Genotypes were a significant source of variation for almost all traits studied (body size, skeletal measurements, histomorphometry of the femur, number of caudal vertebrae) indicating that eighteen generations of artificial selection were successful in modifying phenotypes. Antagonistic selection revealed an association between the mechanisms that regulate skeleton growth and body conformation. Trunk length seemed to be dependent of the biomass a mouse would attain. Femur length and its morphometric characteristics were conditioned by other factors than body weight. The observed response in caudal vertebrae number could be explained if this character is considered as a threshold one. The selective procedure applied in this research was also useful to study other biological characters such as fat deposition, immune reactions and bone biomechanics.

Phenotypic differences on the outcome of the host-parasite relationship: behavior of mice of the CBi stock in natural and experimental infections.

Investigation of defined animal models may help to elucidate the role of the host genetic background in the development and establishment of a parasitic infection. Four lines of mice obtained by disruptive selection for body conformation (CBi+, CBi-, CBi/C and CBi/L) and the unselected control line CBi were examined in their response to different parasites to assess whether these distinct genotypes showed differences in their resistance to natural and experimental parasitosis. Protozoans (Trichomonas muris and Spironucleus muris) and nemathelminths (Syphacia obvelata and Aspiculurus tetraptera) were found naturally parasitizing the mices intestines. CBi/C and CBi were the only genotypes in which T. muris was found. CBi- was least resistant to S. muris. The helminth parasitic burden showed differences between sexes within genotypes (males had a higher burden than females) and among genotypes (CBi/L males had the lowest burden). CBi/L animals were also most resistant to experimental challenge with Heligmosomoides polygyrus and Trypanosoma cruzi. Since all the animals examined shared a common habitat throughout the study and were equally exposed to infection, the phenotypic differences in the natural enteroparasitism herein described evince genetic differences among lines in the host-parasite relationship. This interpretation is further supported by the differences in the response to the experimental challenge to H. polygyrus and T. cruzi.

Asymptotic weight and maturing rate in mice selected for body conformation

Padroes de crescimento de 4 linhagens de camundongos selecionados para a conformacao do corpo foram analisadas com a funcao logistica, de modo a se obterem informacoes basais a respeito da relacao entre o peso assintotico e a taxa de maturacao do peso corporal. Duas linhagens foram selecionadas divergentemente, favorecendo a correlacao fenotipica entre o peso corporal e o comprimento da cauda (selecao agonistica: CBi+, peso corporal elevado e cauda longa; CBi-, peso corporal reduzido e cauda curta), enquanto que as outras duas linhagens foram geradas por uma selecao disruptiva feita contra a correlacao entre os caracteres acima citados (selecao antagonistica: CBi/C, peso corporal elevado e cauda curta; CBi/L, peso corporal reduzido e cauda longa). Os parâmetros logisticos A (peso assintotico) e k (taxa de maturacao) comportaram-se em camundongos CBi/C e CBi- e em femeas CBi+ conforme esperado, em termos da relacao genetica negativa entre o tamanho maduro e a precocidade de maturacao. Um padrao alterado de crescimento foi encontrado em camundongos CBi/L e em machos CBi+, porque no primeiro genotipo, selecionado para reduzido peso corporal, o tempo decorrido para a maturacao aumentou, enquanto que no ultimo, selecionado para elevado peso corporal, houve um aumento nao significante no mesmo carater. De acordo com o criterio de selecao, fontes diferentes de variacao genetica para o peso corporal puderam ser exploradas: uma inversamente associada com precocidade de maturacao (selecao agonistica) e a outra independente da taxa de maturacao (selecao antagonistica), mostrando que a variacao genetica de A e parcialmente independente de k.

Bone mineral deposition in mice selected for body conformation

Bone mineral content was investigated in 2 lines of mice (CBi/C and CBi/L) that carry different biomasses per unit of skeletal weight. These lines also differ in their femoral histomorphometry and bone biomechanics. The logarithmic form of the allometric equation describing the relationship between ash weight and body weight was used to compare the mineral content in both sexes of these genotypes. No statistical difference was observed in the slopes of the curves describing the changes in bone mineral content as a function of age. Both lines had greater values than the line for control animals. The selected lines did differ significantly in the intercepts of the curves on the y-axis. An independent determination of both allometric parameters by genetic factors is proposed. Genes or groups of genes could affect mineral deposition in two ways: one could produce positional changes of the allometric curves in the embryo but leave their postnatal slopes unchanged; another could modify the postnatal slope of the curve. The combined expression of these different genes should be important in preserving homeostatic functioning of the organism.

Effect of immune and normal RNA on the immunological response induced by rat red blood cells in mice

Se inmunizaron ratones BALB con glóbulos rojos de ratas de una línea endocriada. A estos ratones se les extrajo el ARN del bazo y se inyectó a otro grupo de animales de la misma cepa. Además, se inyectó el ARN proveniente de bazo de ratón normal a un segundo grupo de animales. Cinco días después de la inyección del ARN normal e inmune, ambos grupos, y un tercero, testigo, recibieron una inyección de glóbulos rojos de rata.