BI2123_10_Development PDF - Introduction to Development

An Introduction to Development Aurnab Ghose; 241003 Development of multi-cellular organisms Emergence of form and organised structure from an initial single fertilized egg Genes control development by regulating when, where and how much of proteins will be synthesized. (Gene r...

An Introduction to Development Aurnab Ghose; 241003 Development of multi-cellular organisms Emergence of form and organised structure from an initial single fertilized egg Genes control development by regulating when, where and how much of proteins will be synthesized. (Gene regulation) Gene activity establishes intracellular networks of interaction between genes and proteins, and proteins and proteins that give the cells their particular properties. (Intracellular networks & Cell differentiation) A key cellular property is to communicate and coordinate with other cells (Cell-cell interactions) Key processes in development Cleavage divisions Pattern formation Morphogenesis Cell Differentiation Growth These processes overlap and influence each other  Cleavage divisions There is no increase in cell mass during these early divisions  Pattern formation Organizing spatial and temporal pattern of cellular activities that allow a well ordered structure to develop The main body axes are specified : anterior-posterior and dorsal- ventral axes. Early patterning helps establish the overall body plan The basic pattern of the body plan and form of embryo is laid down on a small scale Pattern formation and cell differentiation are closely connected – the former instructing the latter  Pattern formation Maternal effect genes bicoid nanos hunchback caudal Hox genes Homeotic genes (specification)  Pattern formation bicoid nanos caudal Bicoid Hunchback Hox genes Gregor et al, 2007 Pattern formation and specification Pattern formation and specification Wild-type Antennapedia Pattern formation and specification  Morphogenesis Changes in three dimensional form Gastrulation: a striking case of morphogenesis Ectoderm: epidermis (skin) & nervous system Endoderm: gut & derivatives like liver & lungs Mesoderm: skeleto-muscular system, internal organs like heart and kidney. Specification of Germ Layers Development in Xenopus  Cell Differentiation Structural and functional changes in cells due changes in gene expression patterns resulting in distinct cell types  Growth The basic pattern of the body plan and form of embryo is laid down on a small scale Allometric growth: Gene expression à Cell behaviour à Developmental processes Past and current patterns of gene activity confers upon a cell a particular state, or identity, which is reflected in its molecular organisation and function Changing pattern of gene activity is essential for pattern formation - identity - determine future behaviour - lead to final differentiation Cells influence each other Cell movement or shape change generate physical forces that bring about morphogenesis Development is progressive and fate of cell are determined at different times.  The embryo contains a GENERATIVE rather than a DESCRIPTIVE programme Rather than encoding a full description (blueprint) of the final developed form, the genome encodes a series of progressive instructions (generative programme) to build the organism