Causes and consequences of DNA content variation in Zea / Causas y consecuencias de la variación del contenido de ADN en Zea

ABSTRACT Cytogenetic evidence indicates that Zea, which comprises maize (Z. mays ssp. mays) and its wild relatives, is an allopolyploid genus. Our research group has carried out numerous cytogenetic studies on Zea species, mainly focused on native Argentinian and Bolivian maize landraces. We found a wide inter- and intraspecific genome size variation in the genus, with mean 2C-values ranging between 4.20 and 11.36 pg. For the maize landraces studied here, it varied between 4.20 and 6.75 pg. The objectives of this work are to analyze the causes of genome size variation and to discuss their adaptive value in Zea. This variation is mainly attributed to differences in the heterochromatin located in the knobs and to the amount of interspersed DNA from retrotransposons. Polymorphisms in presence or absence of B-chromosomes (Bs) and the population frequency of Bs are also a source of genome size variation, with doses ranging between one and eight in the landraces analyzed here. Correlation analysis revealed that the percentage of heterochromatin is positively correlated with genome size. In addition, populations cultivated at higher altitudes, which are known to be precocious, have smaller genome sizes than do those growing at lower altitudes. This information, together with the positive correlation observed between the length of the vegetative cycle and the percentage of heterochromatin, led us to propose that it has an adaptive role. On the other hand, the negative relationship found between Bs and heterochromatic knobs allowed us to propose the existence of an intragenomic conflict between these elements. We hypothesize that an optimal nucleotype may have resulted from such intranuclear conflict, where genome adjustments led to a suitable length of the vegetative cycle for maize landraces growing across altitudinal clines.

RESUMEN La evidencia citogenética indica que el género Zea, el maíz (Z. mays ssp. mays) y sus parientes silvestres, posee un origen alopoliploide. Nuestro grupo de investigación ha realizado numerosos estudios en especies de Zea, principalmente en maíces nativos de Argentina y Bolivia. En este género, hallamos una amplia variación inter e intraespecífica en el tamaño del genoma, con valores 2C medios que oscilan entre 4,20 y 11,36 pg. El valor 2C medio de los maíces nativos estudiados varió entre 4,20 y 6,75 pg. Los objetivos de este trabajo son analizar las causas de la variación del tamaño del genoma en Zea y discutir su valor adaptativo. Esta variación se atribuye principalmente a las diferencias en la heterocromatina de los knobs y en la cantidad de ADN intercalado de los retrotransposones. Otras fuentes de variación son los polimorfismos para presencia/ausencia de cromosomas B (Bs) y para la frecuencia poblacional de Bs en las razas analizadas, con dosis que oscilan entre uno y ocho Bs. El porcentaje de heterocromatina se correlaciona positivamente con el tamaño del genoma. Las poblaciones cultivadas en altitudes altas, que son precoces, tienen tamaños de genoma más pequeños que las que crecen en bajas altitudes. Esta información, junto con la correlación positiva observada entre la duración del ciclo vegetativo y el porcentaje de heterocromatina, nos llevó a proponer el rol adaptativo de la heterocromatina. Por otro lado, la relación negativa encontrada entre Bs y knobs heterocromáticos nos permitió proponer la existencia de un conflicto intragenómico entre estos elementos. Hipotetizamos que de este conflicto intranuclear habría resultado el nucleotipo óptimo, donde ajustes genómicos condujeron a una duración adecuada del ciclo vegetativo en las razas de maíz que crecen a lo largo de clines altitudinales.

Chromosomal characterization in native populations of Elymus scabrifolius from Argentina through classical and molecular cytogenetics (FISH-GISH).

The karyotype of Elymus scabrifolius (Döll) J.H. Hunz. (2n = 4x = 28) was investigated by DAPI staining and in situ hybridization. All the accessions studied presented a symmetric and uniform karyotype constituted by 9m+2m-sm+3sm. DAPI stain showed 1-7 conspicuous bands in all the chromosomes and polymorphisms between accessions. FISH experiments carried out with 45S rDNA as probe (pTa71) showed strong hybridization signals on the metacentric SAT-chromosome pair 8; the submetacentric SAT-chromosome pair 13 presented weaker hybridization. FISH using pSc119.2 clone as probe identified five chromosome pairs. Then, the combination of chromosome morphology, DAPI-staining, and FISH enabled the accurate identification of each chromosome pair in E. scabrifolius. Genomic in situ hybridization (GISH) experiments using Hordeum DNA as probe on mitotic metaphases confirmed unequivocally the presence of the H genome in E. scabrifolius, allowing us to observe six uniformly labeled chromosome pairs and two chromosome pairs with only one arm labeled. The remaining six chromosome pairs were weakly labeled. The rehybridization of FISH slides with Hordeum DNA as probe allow us to assign the genomic provenance of most of the chromosomes in the studied accessions. Moreover, intergenomic rearrangement was detected between genome H and the still unknown progenitor genome.

[Time course of the myocardial infarction in the rabbit]. / Cronodinamia del infarto de miocardio en el conejo.

The histopathologic evolution of myocardial infarct and of areas distant from infarct in rabbit hearts was studied. The left coronary artery of 55 rabbits was ligated, and rabbits were sacrificed at 2, 4, 6, 8, 12, 14, 16, 18, 26, 35 and 56 days post-ligature (n = 5 per group). Two rabbits were used as control and two were sham operated. The hearts were excised, cut in slices and stained with hematoxilin-eosin, Masson's trichrome and picrosirius red. Histological evaluation was semi-quantitative (scale: 0 to +++). At day 2, presence of neutrophils was +++, disappearing completely at day 6. Fibroblast proliferation increased from day 4 to day 14 post-occlusion. Coagulation necrosis in medial myocardium during the first week was +++. Subendocardic myocytolysis was evident from day 2 up to day 56 post-infarction. During the second week, proliferation of lymphocytes and macrophages (+++), granulation tissue formation (+++), and incipient traces of fibrosis that peaked at day 35 were observed. Cicatrization was complete at day 56 (+++). In areas far from infarction (right ventricle and septum), proliferation of fibroblasts was observed at day 2, and perivascular, interstitial and endocardic fibrosis at day 16. In conclusion, myocardial infarction in rabbits, unlike myocardial infarction in human beings, is characterized by early presence of fibroblasts and subendocardic fibrosis, and quick increase and precocious disappearance of neutrophils. An interesting finding was the early proliferation of fibroblasts in normal areas far from infarct.

Cronodinamia del infarto de miocardio en el conejo. / [Time course of the myocardial infarction in the rabbit]

The histopathologic evolution of myocardial infarct and of areas distant from infarct in rabbit hearts was studied. The left coronary artery of 55 rabbits was ligated, and rabbits were sacrificed at 2, 4, 6, 8, 12, 14, 16, 18, 26, 35 and 56 days post-ligature (n = 5 per group). Two rabbits were used as control and two were sham operated. The hearts were excised, cut in slices and stained with hematoxilin-eosin, Massons trichrome and picrosirius red. Histological evaluation was semi-quantitative (scale: 0 to +++). At day 2, presence of neutrophils was +++, disappearing completely at day 6. Fibroblast proliferation increased from day 4 to day 14 post-occlusion. Coagulation necrosis in medial myocardium during the first week was +++. Subendocardic myocytolysis was evident from day 2 up to day 56 post-infarction. During the second week, proliferation of lymphocytes and macrophages (+++), granulation tissue formation (+++), and incipient traces of fibrosis that peaked at day 35 were observed. Cicatrization was complete at day 56 (+++). In areas far from infarction (right ventricle and septum), proliferation of fibroblasts was observed at day 2, and perivascular, interstitial and endocardic fibrosis at day 16. In conclusion, myocardial infarction in rabbits, unlike myocardial infarction in human beings, is characterized by early presence of fibroblasts and subendocardic fibrosis, and quick increase and precocious disappearance of neutrophils. An interesting finding was the early proliferation of fibroblasts in normal areas far from infarct.

Late systemic-allergic reactions to inhalant allergen immunotherapy.

Late systemic-allergic reactions (defined as occurring between 30 minutes and 6 hours after injection) to inhalant allergen immunotherapy were prospectively studied in four allergy treatment centers; 35,674 injections were administered to 712 patients. Twenty-nine patients (4% of all patients) experienced 33 late reactions. Fifty-six injections (0.16% of all injections) were associated with the 33 late reactions. The most common clinical manifestation of a late reaction was urticaria. However, objective respiratory airway involvement, as manifested by wheezing and/or stridor, occurred in 10 (27%) of the late reactions. Delayed reactions involving wheezing and/or stridor were only related to injections from maintenance vials, and all these more severe reactions occurred no later than 60 minutes after injection. We conclude that late systemic-allergic reactions account for a significant percent of the total number of systemic-allergic reactions to inhalant allergen immunotherapy. It is our belief that a 60-minute postinjection waiting period for injections administered from maintenance vials of extract would enhance the safety of inhalant allergen immunotherapy.

Late and immediate systemic-allergic reactions to inhalant allergen immunotherapy.

Systemic-allergic reactions to allergen immunotherapy were prospectively studied in four allergy treatment centers to assess frequency and specific attributes of these episodes relative to several variables. A total of 20,588 extract injections were administered to 628 patients. Forty-two patients experienced a systemic reaction (7%). Fifty-two systemic reactions occurred in total. Eight patients accounted for 18 of the reactions. Late systemic reactions, occurring from 35 minutes to 6 hours after injection, accounted for 38% of all reactions. Extracts containing only pollen antigens were more commonly associated with immediate and late systemic reactions relative to other extracts (p less than 0.001 and p less than 0.01, respectively). There were no significant reaction-rate differences whether immunotherapy was at maintenance or increasing doses or if the time of injection was during a pollinating or nonpollinating season. The most common clinical manifestations of the systemic reactions were generalized pruritus and urticaria. We conclude that patients receiving extracts containing only pollen antigens have increased systemic-allergic reaction rates. A subgroup of patients are at risk for recurrent reactions. Finally, late systemic reactions to immunotherapy are not rare events and pose a definite risk to the individual patient.

Exposure to ethanol during pregnancy in mice: potential importance of dose for the development of tolerance in offspring.

CD-1 albino mice were given Portagen-10 percent ethanol (ETOH) or isocaloric Portagen-sucrose during pregnancy to determine if tolerance developed in utero and to describe the temporal pattern of its decline postnatally. ETOH mothers did not significantly increase their consumption of ETOH but gained in body weight during pregnancy, showed no signs in the open field of withdrawal from ETOH shortly after delivery and showed less pup-caring behavior than pair-fed controls (PFC). Among offspring 1, 3, 10, 25 and 60 days old, only 25-day old ETOH pups metabolized and cleared an anesthetic dose of ETOH more efficiently than PFC animals, suggesting the absence of Dispositional Tolerance in the other animals. PFC offspring 10 days old took significantly longer to lose the righting reflex than their ETOH counterparts following the anesthetic dose of ETOH, the difference being opposite that which would suggest the occurrence of Adaptive Tolerance. Data are discussed primarily in terms of decreases in dose of ETOH to which mothers and fetuses were exposed during pregnancy.