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Biomedical subjects

R M Ranganath

Publications and source records attributed to R M Ranganath.

6 recordsLinked to original sources
PubMed2005

Asymmetric cell divisions in flowering plants - one mother, "two-many" daughters.

Plant development shows a fascinating range of asymmetric cell divisions. Over the years, however, cellular differentiation has been interpreted mostly in terms of a mother cell dividing mitotically to produce two daughter cells of different fates. This popular view has masked the significance of an entirely different cell fate specification pathway, where the mother cell first becomes a coenocyte and then cellularizes to simultaneously produce more than two specialized daughter cells. The "one mother - two different daughters" pathways rely on spindle-assisted mechanisms, such as translocation of the nucleus/spindle to a specific cellular site and orientation of the spindle, which are coordinated with cell-specific allocation of cell fate determinants and cytokinesis. By contrast, during "coenocyte-cellularization" pathways, the spindle-assisted mechanisms are irrelevant since cell fate specification emerges only after the nuclear divisions are complete, and the number of specialized daughter cells produced depends on the developmental context. The key events, such as the formation of a coenocyte and migration of the nuclei to specific cellular locations, are coordinated with cellularization by unique types of cell wall formation. Both one mother - two different daughters and the coenocyte-cellularization pathways are used by higher plants in precise spatial and time windows during development. In both the pathways, epigenetic regulation of gene expression is crucial not only for cell fate specification but also for its maintenance through cell lineage. In this review, the focus is on the coenocyte-cellularization pathways in the context of our current understanding of the asymmetric cell divisions. Instances where cell differentiation does not involve an asymmetric division are also discussed to provide a comprehensive account of cell differentiation.

Biological Evolution↗
PubMed2004

Harnessing the developmental potential of nucellar cells: barriers and opportunities.

Angiosperm nucellar cells can either use or avoid meiosis in vivo, depending on the developmental context. This unique ability contrasts with the conditions required in vitro, either for a reconstituted oocyte to avoid meiosis and produce clones by somatic cell nuclear transfer (SCNT), or for mammalian stem cells to undergo meiosis and produce synthetic sex cells (gametes). Current biotechnological initiatives to harness the potential of nucellar cells are based on the transfer of apomixis genes to sexual crop plants with the aim of producing clones through seeds. The elusive genetic basis of apomixis compels us to examine whether this process involves epigenetic factors. The elegant and versatile developmental platform available in nucellar cells should be explored as a genome-scale science and compared with mammalian stem cell biology for a holistic understanding of developmental programming and reprogramming in eukaryotes.

Aspartic Acid Endopeptidases↗
PubMed2001

Role of programmed cell death in development.

Programmed cell death (PCD) is an integral part of both animal and plant development. In animals, model systems such as Caenorhabditis elegans, Drosophila melanogaster, and mice have shown a general cell death profile of induction, caspase mediation, cell death, and phagocytosis. Tremendous strides have been made in cell death research in animals in the past decade. The ordering of the C. elegans genes Ced-3, 4 and 9, identification of caspase-activated DNase that degrades nuclear DNA during PCD, identification of signal transduction modules involving caspases as well as the caspase-independent pathway, and the involvement of mitochondria are some of the findings of immense value in understanding animal PCDs. Similarly, the caspase inactivation mechanisms of infecting viruses to stall host cell death give a new dimension to the viral infection process. However, plant cell death profiles provide an entirely different scenario. The presence of a cell wall that cannot be phagocytosed, absence of the hallmarks of animal PCDs such as DNA laddering, formation of apoptotic bodies, a cell-death-specific nuclease, a biochemical machinery of killer enzymes such as caspases all point to novel ways of cell elimination. Large gaps in our understanding of plant cell death have prompted speculative inferences and comparisons with animal cell death mechanisms. This paper deals with both animals and plants for a holistic view on cell death in eukaryotes.

Animals↗
PubMed1997

A chromatographic study of leaf phenolic compounds in two Citrus interspecific hybrids and their parents.

Two interspecific F1 hybrids of Citrus species were examined for inheritance of leaf phenolic compounds. Both the hybrids revealed a reduced number of compounds compared with those of the parents. In addition, the spot pattern of each taxon offered a basis for analysis of inheritance pattern. Due to the production of clones with a consequent reduction in the number of sexual offspring by nucellar embryony in these plants, the unusual pattern of inheritance observed in the hybrids could not be categorized as either a product of disturbed Mendelian ratios or as transgressive segregation affecting only a few individuals in the segregating generations.

Chimera↗