• P Das

      Articles written in Journal of Biosciences

    • Histological effects of vitamin A on the tail amputated tadpoles ofBufo melanostictus

      P Das P Mohanty-Hejmadi

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      Vitamin A has manifold effects on the development, growth and pattern formation of several amphibians. At the same time it causes severe embryonic malformations. The histological changes brought about by vitamin A in the tail tissues of anurans are quite amazing. A common morphological change brought about by vitamin A in tail-amputated tadpoles ofBufo melanostictus include the formation of a large bulbular mass at the distal end of the tail following tail regeneration. Histology revealed that the bulbular mass consisted of notochordal cells only. Other histological changes are: a thickening of the epidermis and the basement membrane, enlargement of the notochord and the nerve cord, thickening of the sheath covering the notochord and the myelin sheath covering the nerve cord and the disorganization of muscle bundles. The significance of such changes is discussed.

    • Cloning of ribosomal RNA genes from an Indian isolate ofGiardia lamblia and the use of intergenic nontranscribing spacer regions in the differentiation ofGiardia from other enteric pathogens

      A K Sil P Das S Bhattacharyya S Ghosh D J Chattopadyay

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      The ribosomal RNA genes from an Indian isolate ofGiardia lamblia have been cloned and characterized with respect to size, composition and copy number. Southern blotting and rDNA cloning ofGiardia lamblia revealed that genes coding for ribosomal RNA (rRNA) are exceptionally small and are encoded within a 5.6 kb genome fragment repeat. The rDNA repeat unit of this isolate was found to be highly G-C rich like other human isolates and the physical map showed severalSmaI sites. There are 132 copies of the rDNA repeat unit per cell in a head to tail arrangement. Two fragments corresponding to intergenic (0.2 kb and 0.3 kb) region and one (0.8 kb) containing both an intergenic region and a small part of the small subunit ribosomal RNA (SS rRNA) have been identified within the rDNA. These were used in heterogeneity studies ofGiardia isolated from two geographic locations as well as in the analysis of cross reactivity with other enteric organisms. In Southern blots, all the three fragments were found to be highly specific for the differential diagnosis ofGiardia spp. from the other enteric pathogens. These findings should help in developing a sensitive and more specific method for the diagnosis of giardiasis over currently available techniques.

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