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Viral double-stranded RNAs of Eimeria spp. of the domestic fowl: analysis of genetic relatedness and divergence among various strains.

Genetic relatedness was examined among putative viral double-stranded RNA (dsRNA) genomes of Eimeria acervilina, E. maxima, and E. necatrix using Northern hybridization. No cross-hybridization was found among these dsRNAs, revealing little sequence homology, if any. In addition, dsRNAs from eight E. acervulina strains collected from different localities in the United States were also examined for genetic relatedness. The putative viral dsRNAs from these eight strains, including the Guelph strain, hybridized with one another to varying degrees, indicating that they are related but divergent.

Animals↗

Developmental dynamics of the bronchial (airway) and air sac systems of the avian respiratory system from day 3 to day 26 of life: a scanning electron microscopic study of the domestic fowl, Gallus gallus variant domesticus.

The lung buds were first conspicuous on day 3 of embryogenesis. They fused on day 4 and the common growth divided into left and right primordial lungs on day 5. Progressively, the lungs elongated, diverged, and advanced towards the respective dorsolateral aspects of the body wall, reaching their definitive topographical locations in the coelomic cavity on day 6. On day 7, they rotated, attached onto the ribs, gradually started to slide into them, and were deeply inserted by day 8. The primary bronchus (PB) first appeared as a solid cord of epithelial cells (day 4) that successively canalized as it invaded the surrounding mesenchyme, extending along the proximal-distal axis of the lung. From day 8, the secondary bronchi (SB) begun to sprout from the PB in a craniocaudal sequence. On day 9, the parabronchi (PR) started to bud from the SB, projecting into the adjacent mesenchyme. They commenced to canalize on day 10 and greatly increased in length, number, and diameter. By day 13, the PR had anastomosed profusely and totally masked the SB. The luminal surface of the PR was lined by a columnar epithelium from which the atria (day 15), infundibulae (day 16), and air capillaries (ACs) (day 18) developed. At hatching (day 21), the ACs were well developed and had anastomosed profusely with the blood capillaries. Of the air sacs (ASs), the abdominal ones appeared earliest (day 5) followed by the cervical ones on day 6. In quick succession, the other ASs were well formed by day 10. After hatching, no further consequential structures formed: only shifts in topographical locations and an increase in size and number occurred. Morphogenetically, the avian respiratory system differs from the mammalian one in certain key aspects: besides the ASs that are unique to it, the lung is exceptionally complex in structure and is essentially mature at the end of the embryonic life.

Air Sacs↗

dsRNA associated with virus-like particles in Eimeria spp. of the domestic fowl.

RNA segments, identified as double-stranded, were found in sporozoites of the Guelph strains of Eimeria acervulina, E. brunetti, E. maxima and E. necatrix and in 8 of 11 strains of E. acervulina obtained from poultry houses across the United States. These RNAs were resistant to RNase A digestion in the presence of high salt concentrations (0.3 M NaCl). On agarose-gel electrophoresis, E. acervulina had one obvious band at 1.7 kb and a faint band at 3.5 kb; E. brunetti had two bands at 2.1 and 3.3 kb, respectively; E. maxima had one band at 4.5 kb; and E. necatrix had two major bands at 4.5 and 5.6 kb, respectively. No dsRNA band was seen in the three strains of E. tenella examined. Virus-like particles were purified by cesium chloride density centrifugation of homogenates of E. necatrix sporulated oocysts. The fraction at peak virus concentration had a buoyant density of 1.39 g ml-1. These virus-like particles were icosahedral, had no envelope and measured 42-44 nm in diameter. Only one RNA band at 5.6 kb was observed when nucleic acids from gradient fractions containing virus were subjected to electrophoresis. The 4.5-kb dsRNA segment of E. necatrix was not associated with a virus-like particle.

Animals↗

Intracellular localization of viral RNA in Eimeria necatrix of the domestic fowl.

The intracellular localization of viral RNA in three different stages of Eimeria necatrix, namely, the first- and second-generation meronts and the macrogamonts, were examined at the light microscopy level by in situ hybridization. Digoxigenin-labeled riboprobes generated from partial cDNA clones from 5.6-kb and 4.5-kb dsRNA (pzenv1 and pzenv2) were used in this study. Viral RNA was found to be confined to the cytoplasm of the eimerian host; no viral RNA was detected in chicken tissue. The intense hybridization signal observed in the cytoplasm of the immature meronts with the SP6 riboprobe of pzenv1 or the T7 riboprobe of pzenv2 was probably due to their hybridization to positive strands that had been extruded from the virus during transcription. In mature meronts the intensity of the signal is lower, signifying a decrease in transcription activity. Viral replicase activity may thus be synchronized with the growth phase of the eimerian host.

Animals↗