Neural Stem Cells
The nervous system is comprised of specialized type of cells called Neural Stem Cells (NSCs). These cells undergo differentiation and proliferation resulting to a mass of undifferentiated cells. This progeny then undergoes differentiation into the many cells of the nervous system. From neural stem cells, cell of central nervous system such as astrocytes, neurons, ependymal cells and oligodendrocytes are formed.
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Developmental versatility of plasticity of neural stem cells is important in formation of these different neural cells. A NSC can either be embryonic stem cell of adult stem cell. Embryonic stem cells are fully versatile and can form any cell type. On the other hand, adult stem cells have no versatility to form any cell type but replace multipotent cells when they wear out or die. In this regard, embryonic stem cells can either be totipotent, pluripotent or multipotent.
Totipotent stem cells are the most potent cells and can therefore give rise to any type of body cell. Pluripotent stem cells can give rise to body tissues but lack full potency to give rise to any cell type. Multipotent stem cells are the least plastic cells and can only form certain cell types.
Neural cell division (neurogenesis) is an important process in brain development but it needs to be regulated during adulthood development. The best understood neural cell differentiation pathways are sparked by growth factors. Certain set of growth factors are optimal for development of certain stages of neural stem cells. For instance, fibroblast growth factors (FGF) are selective for development of early neural stem cells. This means that in absence of FGF, there occurs a significant reduction in the number stem cell divisions.
For the purposes of studies, multipotent stem cells can be isolated from brain tissue or embryonic stem cells. This can be achieved through co-culture of embryonic stem cells in stroma or conditioned medium. These cells can then be preserved for use in studies together with other cell type-models. These cells and models have enhanced the understanding of the processes involved during brain development.
Stem cell isolation from embryonic cells in central nervous system and in periphery nervous system is achieved through direct means. A neural puncture is usually made and the cells cultured in medium. Apart from stem cell isolation from brain, other regions (hippocampus and ventricular zone) can be used during isolation of adult stem cell.
Viral Vectors in Gene Therapy
Gene therapy refers to a medical application of genetics where genetic transformations are utilized in therapeutic functions. This field has objectively transformed medical fields especially in treatment of chronic disease which are hard to cure by use of chemotherapy e.g. cancer.
This exercise requires transfer of target genes into target cells of the patient. In so doing, a transfer agent called a vector is important. Viruses have lately been found useful as vectors. A good example of a virus that has been used in gene therapy is Adenovirus. It has been found out that this genus of viruses have a good profile to transfer target genes to target cell. They have been used substantially in cancer gene therapy and in biomedicine.
Replication-defective adenovirus has extensively been used as a vector to transfer transgenes to targeted cancerous cells and tumors. On the other hand, oncolytic adenoviruses which have capacity to replicate have been used to kill or transfer therapeutic genes to infected target cells.
Viral vectors have been developed through altering the viral genome making its expression impossible. For instance alteration of E1A gene of Adenovirus genome led to a replication-defective strain. E1A gene is important in ensuring that viral genome is expressed and therefore it can induce its multiplication of host cell. Replication-competent adenoviruses are made by integrating a therapeutic gene in their genome.
Restriction enzymes are an important part in many genetic applications. They enable genome excision by recognizing specific recognition sites along a genetic strand. Excision is important as it allows formation of recombinant genetic strands. A major source of restriction enzymes is bacteria.
Bearing in mind that bacterial genetic material has similar properties to any other genetic material; one may wonder why their DNA remains intact in presence of restriction enzymes. This is possible because restriction enzymes have a way of differentiating between self DNA and non-self DNA. This is possible because Bacterial DNA has other groups attached to their nucleotide sequences. These may be methyl group and/or carbohydrates.
Restriction enzymes were discovered way back in 1952. Their mode of functioning was however not well known until 1960 when Wemer Arber presented his findings with the help of Dussoix at the First International Biophysics Congress. Their research was accompanied by two theories that there was an enzyme in host bacterial cell that cuts its DNA at specific sequences and that host DNA was unaffected due to the presence of methylase. The research earned them the Plantamour-Prevost prize.
Restriction enzyme was first isolated in Escherichia coli by Meselson and Yuan. The enzyme was essentially seen to offer protection of the DNA from the viral DNA which would infect the cells.