Question

explain how the following processes each contribute to animal development: regional specification, cell differentiation, morphogenesis, growth, and developmental time (also known as temporal control). Use citations from peer-reviewed scientific journal articles or the textbook to support your ideas.

Answer 1

Regional specification, cell differentiation, morphogenesis, growth, and developmental time are all the processes that are involved in the development of an embryo and determine the developmental fate of the organism. All these processes together contribute to the development of an organism from a single cell. The processes essentially determine the fate of a cell at each step of development, from the stage where all the cells are initially similar, to a stage where each cell type is unique on its own.

The first step in the process of development (in terms of development) is a regional specification. The regional specification refers to the processes of spatial organization or pattern formation in which cells in different regions of the embryo are stimulated to go through different pathways of development. Regional specification determines which region of the embryo forms which part of the body.

However, the regional specification is different from cell differentiation. During regional specification, different signals or transcription factors influence the cells to adopt different developmental pathways. Since development is controlled relatively by a small number of genes, the genes which play a critical role in regional specification and development are called “master control genes.”

Cell differentiation is a process by which cells of different functional type arise from a common ancestor/progenitor cell. The cells that truly define the function of a tissue are terminally differentiated cells. For example, red blood cells (RBC) are the terminally differentiated cell which performs the function of carrying oxygen. Hepatocytes, neurons, rod and cones of the eye, are all examples of differentiated cells.

The characteristic of a differentiated cell is that it produces large amounts of some specific proteins or enzymes required for their specific function. Differentiation is achieved through a series of steps after the commitment of a progenitor cell to differentiate. A group of signal proteins together influence the cell to differentiate. Sequential turn on and turn off of a group of genes at each step makes the cells express new protein combinations or turn off expression of proteins as a result of which, the cells can interact with new signals and differentiate. Cell differentiation creates different types of cells and tissues.

The formation of complex shapes of adults from the simple ball of cells that is formed from the fertilized egg is called morphogenesis. Morphogenesis establishes the body plan and architecture of mirror-image bilateral symmetry of musculoskeletal structures. Morphogenesis is not required for those organisms which do not have body symmetry. Morphogenesis required the following three important factors:

• Inducive signals for morphogenesis
• Stem cells that respond to the signals
• Extracellular matrix scaffolding

Growth in animals is defined as an increase in body size. The maximum size an animal can grow is determined by its genetics. Nutrition and diseases also determine if an animal can reach its genetic potential for size or now. Animals growth occurs in two stages; prenatal and postnatal growth. The body patterns and shape are formed during the prenatal stage. Postnatal growth generally involves an increase in body size with some changes in the musculoskeletal pattern. Muscle, bone, and fat are the three main tissues that develop after birth. Bone growth occurs only up to a certain age, and thereafter, resorption starts. Muscle growth may slow down after a certain age, but does not stop completely. Fat deposition occurs at any time of life. During early stages of life, growth occurs very quickly.

The development and morphogenesis of an organism not only requires right place (the mother’s womb or egg where all the necessary factors for development are provided) but also requires the processes to occur at a proper time. Coordination of the processes like cell proliferation, differentiation, and spatial patterning through time ensures that the processes occur in correct order or sequence, and the development occurs at a proper pace. The processes that control developmental time are poorly understood. However, certain primitive cell types like presomitic mesoderm direct development of cells in proper time.