Stem Cell Culture and Organ Culture — NCERT Solutions

Stem cells are non-specialised, immature cells with two key properties: self-renewal and potency. They can divide repeatedly by mitosis to produce more stem cells, and they can also differentiate into specialised cell types. In humans, they are found in the umbilical cord, placenta, inner cell mass of the early embryo, foetal tissues, and some adult organs. They are useful in developing new cells, studying diseases, and testing drugs.

• Totipotent stem cells: have the highest potential; they can form all cell types of the body, including embryo and extra-embryonic membranes. A zygote is totipotent.
• Pluripotent stem cells: can form almost all cell types of the embryo, but cannot form extra-embryonic tissues like placenta and yolk sac. They can form all three germ layers.
• Multipotent stem cells: can differentiate into a closely related family of cells within a particular lineage, such as blood cells from haematopoietic stem cells.

So, the main difference is the range of differentiation potential, which decreases from totipotent → pluripotent → multipotent.

Embryonic stem cells are self-reproducing pluripotent cells derived from the inner cell mass or epiblast of the blastocyst. They can give rise to all three germ layers—ectoderm, mesoderm and endoderm.

They differ from adult stem cells in these ways:

• Embryonic stem cells are found in the early embryo; adult stem cells are present in mature tissues, umbilical cord and placenta after birth.
• Embryonic stem cells are pluripotent and more promising for clinical use.
• Adult stem cells are usually multipotent or totipotent, and are mainly responsible for repair and maintenance of tissues.
• Use of embryonic stem cells involves technical safety issues and ethical dilemmas, whereas adult stem cells have no such major controversies.

Stem cells are used for several purposes:

• to develop new cells in vitro and replace damaged tissues or organs
• to study genetic defects and the causes and treatment of diseases
• to test new lead molecules as drugs

Some medical applications mentioned in the chapter are:

• treatment of neurological diseases like ALS and spinal cord injury
• eye diseases using retinal cells
• wound healing and skin replacement
• treatment of cardiovascular diseases
• treatment of auto-immune disorders such as type 1 diabetes, multiple sclerosis and arthritis
• use in drug screening and disease models in pharmaceutical industries

During stem cell culture, the important parameters to be monitored are the general conditions needed for healthy growth of cells, such as:

• sterility/contamination-free conditions
• proper nutrient medium
• suitable temperature and pH
• adequate gas exchange (especially oxygen and carbon dioxide)
• proper cell growth, self-renewal and differentiation

The chapter emphasises that stem cells must be maintained under carefully controlled in vitro conditions so they remain viable and do not undergo unwanted differentiation or contamination.

Organ culture is the development of a part of an organ or the whole organ from tissue culture techniques for research. In organ culture, pieces of an organ are explantated and grown in vitro so that the anatomical relationship and physiological functions of the tissue components are preserved, simulating the parent tissue.

The main characteristics of organ culture are:

• Structural integrity: the native structure of the tissue is preserved; cell-to-cell communication and association remain intact.
• Nutrient and gas exchange: because there is no vascular system, nutrient supply and gas exchange are limited by diffusion; tissues are often kept at a gas–liquid interface.
• Growth and differentiation: organ culture generally shows limited growth, mainly at the outer layers, but it preserves the tissue environment and supports differentiation with the help of soluble growth factors.

Thus, organ culture maintains the structure and function of tissue better than simple cell culture.

The chapter describes three types of organ culture:

1. Whole embryo culture

• The entire embryo is cultured outside the body under controlled conditions.
• Example given: chick embryo cultured on a watchglass with suitable medium.

2. Histotypic culture

• A characterised cell line is cultured at high density with suitable soluble factors and extracellular matrix.
• It helps cells form tissue-like structures, such as capillary tubules in collagen.

3. Organotypic culture

• Cells of different lineages are co-cultured to create a tissue-like structure.
• This is used to maintain interactions between different cell types, for example fibroblast and epithelial cells.

Advantages of organ culture over cell culture are:

• It preserves the whole three-dimensional structure of the organ.
• It maintains the anatomical relationship among tissue components.
• Cell-to-cell communication and association are better preserved.
• It allows study of the actual behaviour of a tissue more realistically than cell culture.
• It is useful for understanding the biochemical and functional characteristics of organs and their comparison with in vivo conditions.
• It helps in studying developmental biology, tissue interaction, and hormone effects.

So, organ culture gives a more natural tissue environment than ordinary cell culture.

Applications of organ culture include:

• using cultured organs as a substitute for organs when transplantable organs are scarce
• enabling transplantation using the patient’s own stem cells, which can reduce the need for immunosuppressive drugs
• studying the actual behaviour of tissues in vitro
• understanding the biochemical and functional characteristics of tissues and organs
• comparing organ function with in vivo organs
• studying the effects of hormones, alone or in combination
• useful in developmental biology and tissue interaction studies