cell lineage and fate

cell lineage , cell fate - diverse class of cell fate, cell fate in plant meristem, mammalian development cell fate, nutritional effects on epigenetics, epigenetics of plants,
control of cell fate.

1. CELL FATE AND LINEAGES M.SC botany

2. Cell lineage  studies aim to define the developmental history of a particular cell type from its precursors through their fully differentiated state. The first cell lineage studies were performed by Whitman at the end of the nineteenth century and consisted of the direct observation of cleavage patterns in leech embryos . Cell lineage  

3. Since then, multiple techniques have been developed to follow the fate of cells, including injections of vital dyes or radioactive molecules in cells of different organisms, introduction of reporter genes by transfection or viral infection, and transplantation of embryonic cells and tissues. More recently, generation of genetically modified mice expressing reporter genes or  Cre recombinase  have provided major advantages for tracing different  cell lineages . Cre recombinase is a site-specific recognition enzyme that recognizes 34 base-pair  LoxP  sequences and, depending on their orientation, excises or inverts the DNA flanked by them. 

4. Cre recombinase DNA

5. It was found that in some animal groups, such as nematodes and ascidians, the pattern of cell divisions was almost identical from individual to individual. Such ‘invariant’  cell lineages  allowed the reconstruction of extensive lineage trees. In other animals, such as leeches and insects, stereotyped patterns of cell division (‘ sublineages ’) were seen in the progeny of particular precursor cells. Because of the correlation between  cell lineage  and cell fate in such invariant lineages, it was assumed that cell fates were determined by factors segregating within the dividing cells (termed ‘determinate’ cleavage).  C ell lineage is defined as the pattern of cell divisions in the development of an organism, whether invariant or not.

6. Cell lineage  is the framework for understanding cellular diversity, stability of differentiation, and its relationship to pluripotency. C. elegans : model organism As one of the first pioneers of cell lineage, in the 1960s  Dr. Sydney Brenner  first began observing cell differentiation and succession in the nematode  Caenorhabditis elegans . Dr. Brenner chose this organism due to its transparent body, quick reproduction, ease of access, and small size which made it ideal for following cell lineage under a microscope. By 1976, Dr. Brenner and his associate,  Dr. John Sulston , had identified part of the cell lineage in the developing nervous system of  C. elegans . Recurring results showed that the nematode was  eutelic  (each individual experiences the same differentiation pathways). This research led to the initial observations of programmed cell death, or apoptosis.

7. After mapping various sections of the  C. elegans ' cell lineage, Dr. Brenner and his associates were able to piece together the first complete and reproducible  fate map  of cell lineage. They later received the 2002 Nobel prize for their work in genetic regulation of organ development and programmed cell death.

8. Cell fate is specified by signaling pathways such as the nodal, fibroblast growth factor ( fgf ), and bone morphogenetic protein (bmp) families during the late blastula stage. Stem cell fate is determined by intrinsic regulators and extrinsic signals. The physiological environment provides a perfect but complex combination of signaling, including the appropriate identity, abundance, location, and dynamics of stimuli that function in synergy with the intrinsic regulatory network to orchestrate the temporal-spatial control of self-renewal and differentiation. CELL FATE

9. DIVERSE CLASS OF CELL FATE

10. CELL FATE IN PLANT MERISTEM

11. The shoot apical meristem is initiated during embryogenesis and, after germination of the seed, it produces the stem, a succession of leaves and flowers. The meristems of  Arabidopsis  are organized into an outer tunica, consisting of two cell layers (L1 and L2), and an inner corpus (L3), which all contribute to organ formation and growth Cell divisions within the L1 and L2 are perpendicular to the surface of the meristem (anticlinal), so that progeny cells will remain in their layer of origin and establish a clone. The cells within one clone can have diverse fates: e.g., a stem cell in the L2 can produce daughter cells that eventually differentiate as subepidermal cells, or even as gametes.  Both leaves and flowers originate on the flanks of the meristem from the peripheral zone that surrounds the central zone, where the stem cells reside

12. Cell Fate in Mammalian Development 1) Cell fate commitment is achieved by the establishment of   epigenetic mechanisms . E pigenetic mechanisms - Epigenetic mechanisms regulate gene expression at the transcription level by modulating the accessibility of gene promoter regions to transcriptional machinery. 

13. E pigenetic mechanisms  of gene expression can be influenced by the environment. One such well-established environmental factor that is known to influence epigenetic mechanisms of gene expression is an individual’s  nutrition . An individual’s nutrition is comprised of water, metabolic fuels (mainly carbohydrates and lipids), proteins, minerals, vitamins, and  essential fatty acids . Nutritional Effects on Epigenetics

14. Epigenetics of Plants Plants use epigenetic mechanisms during development and also across successive generations of whole plants. DNA  methylation , modification of  histones , and small RNAs are used as epigenetic mechanisms, as in most animals. For example, in some  flowering plants , differences in the shape of the flower or color of the fruit are stable across generations and are due to inherited differences in the level of promoter methylation. Methylation  of DNA in plants controls such developmental characteristics as in the ripening of fruits.

15. METHYLATED HISTONE OCTAMER HISTONE OCTAMER

16. Methylation Controls Ripening of Fruit When their promoters are methylated, genes involved in plant ripening are silenced. During development, methyl groups are removed which allows the transcription factor RIN to bind to the promoters. This allows gene expression and the fruit will ripen.

17. 2) While the fertilized egg and very earliest  blastomeres  are totipotent, progressive stages of  embryonic development  lead to restrictions in cell fates and developmental potential. 3) As development proceeds germ cell precursors become reprogrammed, and thereafter become specialized as they differentiate into sex-specific  gametes  exhibiting specialized  epigenomes . Epigenome means genome-wide epigenetic regulations, including DNA methylation, post-translational modification of histone, chromatin remodeling, higher-order DNA organization, and noncoding RNA alterations, all of which are heritable and sequence-independent.

18. stages of  embryonic development  

19. The epigenome of male and female  gametes  at the time of syngamy is a product of a long, complex reprogramming process starting with the naïve epigenome of the primordial  germ cells  (PGCs). Epigenomes are sensitive to environmentally induced alterations in gene expression. These  epigenetic modifications  can result in reproductive, behavioral, and  metabolic disorders . Apart from the direct effect on individual epigenomes, the alteration in the  germline  can transmit the disorders through generations.

20. Stem cell fate is determined by intrinsic regulators and extrinsic signals. The physiological environment provides a perfect but complex combination of signaling, including the appropriate identity, abundance, location, and dynamics of stimuli that function in synergy with the intrinsic regulatory network to orchestrate the temporal-spatial control of self-renewal and differentiation.  CONTROL OF CELL FATE 4) Erasure of these gamete-specific features is then necessary to enable acquisition of a totipotent state in the zygote.

21. Some  in vivo  data support the notion that cell fate can be altered by ethanol exposure. Prenatal exposure to ethanol alters the fates of hematopoietic progenitors in the bone marrow of mouse neonates, and lymphocyte development is delayed. Ethanol can affect the differentiation of cycling and recently postmitotic cells via targeted alterations of genetic expression .