Maria Susana Merani

Meiotic behavior of the X1X2Y1Y2 quadrivalent of the primate Alouatta caraya

A multiple sex chromosome system was found in three unrelated individuals of the primateAlouatta caraya. This mechanism is originated by a translocation between the Y chromosome and one of the autosomes (A7). Mitotic karyotypes show two small, acrocentric chromosomes (AY and YA), which are the translocation products. In metaphase I of male meiosis, there is a very long chain quadrivalent in which the order of the element is: X−YA−A7−AY. Segregation in the quadrivalent is alternate and gives balanced products. Synaptonemal complex karyotypes at pachytene show the structure of the quadrivalent made by the four axes. There is a slight difference in the relative length of AY and YA and the kinetochore of A7 aligns with that of AY. The synaptic pattern and changes in the quadrivalent during pachytene are described. Thin sections of the quadrivalent body show that the chromatin packing in the sex chromosome region is different from that of the autosomal region. This X1X2Y1Y2/X1X1XX2 sex chromosome system may be extended among other members of the genusAlouatta.

Vertical Transmission of Junin Virus in Experimentally Infected Adult Calomys musculinus

The response to infection with Junin virus, wild strain Cba An 9446, and the antenatal and postnatal transmission of the pathogen in its natural host, Calomys musculinus, were studied. Intranasal infection in adult animals (90-120 days) did not produce mortality or illness during the 150-day period of observation. From day 21 to 150 after infection, 50% of the animals showed viral persistence with shedding of virus in both urine and saliva. The remaining half became seropositive, and no infectious virus was recovered from them. Although the virus did not infect fetuses during gestation, 50% of weaned pups nursed by viremic mothers were infected. Neither persistence nor immunologic response altered the reproductive pattern of the animals. The absence of reproductive failure in the infected host and the efficiency of postnatal transfer of Junin virus indicate that vertical transmission could contribute to the viral maintenance over time.

Spermatogenesis is seasonal in the large hairy armadillo, Chaetophractus villosus (Dasypodidae, Xenarthra, Mammalia)

Very little is known about the distinct reproductive biology of armadillos. Very few studies have investigated armadillo spermatogenesis, with data available only for Euphractus sexcinctus and Dasypus novemcinctus. In the present study, we analysed male germ cell differentiation in the large hairy armadillo Chaetophractus villosus throughout the year, describing a cycle of the seminiferous epithelium made of eight different stages. Evaluation of the testis/body mass ratio, analysis of the architecture of the seminiferous epithelium and the frequency of defective seminiferous tubules allowed identification of a temporal interruption of spermatogenesis during the period between mid-May to July (mid-end autumn) in correlation with very low testosterone levels. Overall, these results suggest that spermatogenesis is seasonal in C. villosus.

Calomys laucha (Rodentia, Cricetidae): growth and breeding in laboratory conditions.

The husbandry and breeding of Calomys laucha (Rodentia, Cricetidae) in captivity are described. Growth curves based on body weight and length showed statistical differences between sexes after 45 days, males being heavier than females. The overall reproductive efficiency was 53·4% but birth rate was depressed during winter. Gestation length was 21±1 days and females exhibited postpartum oestrus with a 3-7 day implantation delay (51%). Litter size was 5·3×1·1 (n=34). Pup survival at weaning was 84·9%. Mean life span in laboratory conditions was 13·5 months and a cumulative mortality of 90% was reached at 27-28 months of age.

Is Vertical Transmission Sufficient to Maintain Junin Virus in Nature

The quantitative contribution of vertical transmission to the prevalence rate of Junin virus infection in subsequent generations of its natural reservoir, Calomys musculinus, was analysed. Data on mortality and reproduction of C. musculinus infected at birth with a wild strain of Junin virus were used to estimate the infection-dependent relative survival rate (beta = 0.4849) and relative fertility of the infected host (alpha = 0.2088). Prevalence rates of infection, obtained by mathematical simulation in optimal conditions of vertical transfer, dropped steadily to zero in a few generations. Vertical transmission was found to be insufficient to overcome the effect of highly depressed survival and fertility of the infected host and maintain a stabilized prevalence of Junin virus infection in successive generations; this suggested that viral maintenance is mainly dependent upon horizontal transmission.

Loss of Sertoli-Germ Cell Adhesion Determines the Rapid Germ Cell Elimination During the Seasonal Regression of the Seminiferous Epithelium of the Large Hairy Armadillo Chaetophractus villosus

ABSTRACT The armadillo Chaetophractus villosus is a seasonal breeder whose seminiferous epithelium undergoes rapid regression with massive germ cell loss, leaving the tubules with only Sertoli cells and spermatogonia. Here, we addressed the question of whether this regression entails 1) the disassembly of cell junctions (immunolocalization of nectin-3, Cadm1, N-cadherin, and beta-catenin, and transmission electron microscopy [TEM]); 2) apoptosis (immunolocalization of cytochrome c and caspase 3; TUNEL assay); and 3) the involvement of Sertoli cells in germ cell phagocytosis (TEM). We showed a dramatic reduction in the extension of vimentin filaments associated with desmosomelike junctions at the interface between Sertoli and germ cells, and an increased diffusion of the immunosignals of nectin-3, Cadm1, N-cadherin, and beta-catenin. Together, these results suggest loss of Sertoli-germ cell adhesion, which in turn might determine postmeiotic cell sloughing at the beginning of epithelium regression. Then, loss of Sertoli-germ cell adhesion triggers cell death. Cytochrome c is released from mitochondria, but although postmeiotic cells were negative for late apoptotic markers, at advanced regression spermatocytes were positive for all apoptotic markers. Transmission electron microscopy analysis showed cytoplasmic engulfment of cell debris and lipid droplets within Sertoli cells, a sign of their phagocytic activity, which contributes to the elimination of the residual meiocytes still present in the latest regression phases. These findings are novel and add new players to the mechanisms of seminiferous epithelium regression occurring in seasonal breeders, and they introduce the armadillo as an interesting model for studying seasonal spermatogenesis.

Seasonal changes in ovarian steroid hormone concentrations in the large hairy armadillo (Chaetophractus villosus) and the crying armadillo (Chaetophractus vellerosus)

Knowledge of armadillo reproductive physiology is essential for developing ex situ and in situ assisted reproductive techniques for propagating and/or controlling populations of these animals. The present study included assessment of fecal sex steroids by radioimmunoassay, determining reproductive status via monitoring ovarian activity (in the wild) and therefore reproductive status, in wild females of the large hairy armadillo (Chaetophractus villosus) and the crying armadillo (Chaetophractus vellerosus) in the southern hemisphere. Plasma and fresh fecal progesterone concentrations were not significantly correlated in either species. However, in both species, there was a significant positive correlation between plasma progesterone and dry fecal progesterone concentrations (r = 0.82, P < 0.05 and r = 0.60, P < 0.05, respectively). Dry fecal progesterone and estradiol concentrations were measured in one captive C. villosus (average baseline progesterone and estradiol concentrations 28.72 ± 11.75 ng/g dry feces and 3.04 ± 0.80 ng/g dry feces, respectively) and one captive C. vellerosus (average baseline progesterone and estradiol concentrations 14.05 ± 3.03 ng/g dry feces and 3.46 ± 1.20 ng/g dry feces, respectively) to detect hormonal peaks over 1 y; these occurred from late fall to early summer. Feces from wild C. villosus and C. vellerosus were also collected over 1 y to determine progesterone peaks, which occurred in winter and spring in both species (with no peaks during the summer or fall). Accordingly, C. villosus and C. vellerosus had a seasonal reproductive pattern. The significant correlations between dry fecal and plasma progesterone concentrations validated this method for monitoring reproductive status in these species.

Chromosomal localization of the telomeric (TTAGGG)n sequence in four species of Armadillo (Dasypodidae) from Argentina: an approach to explaining karyotype evolution in the Xenarthra

The distribution of the vertebrate telomeric sequence (TTAGGG)n in four species of armadillos (Dasypodidae, Xenarthra), i.e. Chaetophractus villosus (2n = 60), Chaetophractus vellerosus (2n = 62), Dasypus hybridus (2n = 64) and Zaedyus pichiy (2n = 62) was examined by FISH with a peptide nucleic acid (PNA) probe. Besides the expected telomeric hybridization, interstitial (centromeric) locations of the (TTAGGG)n sequence were observed in one chromosome pair of Chaetophractus vellerosus and Zaedyus pichiy, suggesting chromosome fusion of ancestral chromosomes occurring during the evolution of Dasypodidae. In addition, all the species analysed showed one to four apparently telocentric chromosomes, exhibiting only two telomeric signals. However, the immunodetection study of kinetochore proteins on synaptonemal complex spreads from C. villosus showed that the apparently telocentric chromosomes have a tiny short arm that can be resolved only in the more elongated pachytene bivalents. This finding suggests that none of the species of armadillos possess true telocentric chromosomes. Our present results support a reduction in the diploid number by fusion of acrocentrics with loss of chromosome material as a tendency in Dasypodidae.

Robertsonian chromosome polymorphism of Akodon molinae (Rodentia: Sigmodontinae): analysis of trivalents in meiotic prophase

Akodon molinae con 2n = 42-43-44 y FN = 44 presenta un notable polimorfismo en el cromosoma 1 en poblaciones naturales y de laboratorio, los individuos 2n = 42 tienen un par 1 formado por dos cromosomas metacentricos grandes y son denominados homocigotos simples (SH); los individuos 2n = 43, heterocigotos (Ht), presentan un cromosoma 1 y dos cromosomas subtelocentricos de tamano medio 1a and 1b, que son homologos con los brazos largo y corto del 1, respectivamente; y los individuos 2n = 44 que son los doble homocigotos (DH) y presentan dos pares de cromosomas subtelocentricos 1a y 1b. Analisis de la metafases I y II meioticas han demostrado que se producen segregaciones anomalas con una alta frecuencia en los espermatocitos portadores de los cromosomas 1a and 1b. Ello alteraria a otros procesos, como la gametogenesis, la reproduccion y el desarrollo, disminuyendo la viabilidad individual y poblacional de los DH. No ha habido una explicacion satisfactoria para estos fenomenos. Para investigar elementos estructurales que pudiesen explicar tales alteraciones segregacionales, se estudio la sinapsis de bivalentes y trivalentes en espermatocitos en paquiteno de ejemplares SH, Ht y DH. De un total de 80 microesparcidos de nucleos de espermatocitos: en 16 nucleos de ejemplares SH se observaron 20 bivalentes autosomicos mas el bivalente XY; en 48 nucleos de Ht se observaron 19 bivalentes autosomicos, 1 trivalente y un bivalente XY; y en 16 nucleos de DH se observaron 21 bivalentes autosomicos mas el bivalente XY. Los trivalentes analizados mostraron apareamiento completo entre los brazos cortos de 1a y 1b conformandose un complejo sinaptonemico (CS) aparentemente normal con una longitud entre 1 µm y 2,8 µm. El CS de los trivalentes presento tres extremos telomericos correspondientes a los brazos: q1 y q1a, p1 y q1b y p1a y p1b, con placas de insercion a la envoltura nuclear de organizacion normal. En ninguno de los trivalentes se observo asinapsis o desinapsis entre p1a y p1b, ni asociaciones con el bivalente XY. En el 70 % de los espermatocitos estudiados el bivalente XY mostro apareamiento completo entre X e Y, con formacion de CS en toda la longitud del cromosoma Y. El 30 % restante presento apareamiento parcial con un CS de longitud variable a partir del extremo comun. Sobre la base de los resultados de este trabajo y los antecedentes existentes, se discute: 1.- que la configuracion obligada del trivalente con formacion de CS entre los brazos cortos de 1a y 1b, contribuye a asegurar la segregacion cuasi normal entre 1, 1a y 1b en la I anafase de la meiosis de los Ht; y 2.- que la coexistencia en los trivalentes de los cromosomas 1, 1a y 1b en los Ht, erosiona la integridad estructural y funcional de los brazos cortos de 1a y 1b, dano que seria acumulativo y que explicaria la viabilidad disminuida de los individuos portadores de estos cromosomas

The rete mirabile of the tail, an effective site for sampling sterile blood from armadillos (Dasypodidae, Xenarthra)

Abstract Armadillos constitute a neotropical endemic mammalian group in the American continent and the main diversity is distributed in Argentina. Several species of this family are in danger of extinction. Blood collection in armadillos is difficult because of their anatomy. In the present work, in latex-perfused material, the rete mirabile of the coccygeal artery of the tail was recognized as an appropriate venipuncture site for sterile blood collection. From cadaveric material, histological sections of the tail of six species of five genera of armadillos were used to determine the diameter and the distance to access the main artery of the rete mirabile ventrodorsally. Field studies were carried out in wild animals. A total of 232 blood samples were obtained from the following species: Chaetophractus villosus (70), C. vellerosus (105), Zaedyus pichiy (15), Euphractus sexcinctus (8), Dasypus hybridus (25), and Tolypeutes matacus (9). The animals were restrained with the thumbs pressing the abdomen ventrolaterally and the rest of the fingers holding the carapace. Punctures were carried out between the first and second rings of the tail with a 21-gauge needle. Alternatively, an immobilization device was designed to allow sampling by a single operator. Blood cell integrity was evaluated through histological analysis and ulterior development in lymphocyte culture. We concluded that the rete mirabile of the tail of armadillos is an effective venipuncture site for field studies that allows obtaining sterile blood samples, avoiding animal mortality, high-risk venipuncture sites, anesthetics and excessive stress.