EARLY DEVELOPMENT in MAMMALS

1. EARLY DEVELOPMENT in MAMMALS

2. Overview of Development Development is the successive process of systematic gene-directed changes throughout an organism�s life cycle -Can be divided into four subprocesses: -Growth (cell division) -Differentiation -Pattern formation -Morphogenesis

3. Principles of Embryonic Development Fertilization results in a zygote and triggers embryonic development

5. The process of fertilization Only one of these sperm will penetrate this human egg cell to initiate fertilization Fertilization is the union of a sperm and an egg to form a diploid zygote

6. Cell Division Cleavage is the first major phase of embryonic development It is the rapid succession of cell divisions It creates a multicellular embryo from the zygote It partitions the multicellular embryo into developmental regions

7. Cell Division After fertilization, the diploid zygote undergoes a period of rapid mitotic divisions is called cleavage -Controlled by cyclins and cyclin-dependent kinases (Cdks) During cleavage, the zygote is divided into smaller & smaller cells called blastomeres

8. Blastomeres are nondifferentiated and can give rise to any tissue. Stem cells are set aside and will continue to divide while remaining undifferentiated. -Tissue-specific: can give rise to only one tissue -Pluripotent: can give rise to multiple different cell types (Blastocyst-inner cell mass) -Totipotent: can give rise to any cell type (Morula stage )

9. Cleave in mammals continues for 5-6 days producing a ball of cells, the blastocyst -Consists of: -Outer layer= Forms the placenta (Trophoblast cell that secretes enzymes to enable the blastocyst to implant in the uterine wall)

12. Cell Differentiation A human body contains more than 210 major types of differentiated cells Cell determination commits a cell to a particular developmental pathway -Can only be �seen� by experiment -Cells are moved to a different location in the embryo -If they develop according to their new position, they are not determined

13. Cell Differentiation Cells initiate developmental changes by using transcriptional factors to change patterns of gene expression Cells become committed to follow a particular developmental pathway in one of two ways: 1) via differential inheritance of cytoplasmic determinants 2) via cell-cell interactions

14. Gastrulation produces a three-layered embryo Gastrulation is the second major phase of embryonic development and produces a three-layered embryo It adds more cells to the embryo It sorts all cells into three distinct cell layers The embryo is transformed from the blastula into the gastrula

15. The three layers produced in gastrulation Ectoderm, the outer layer Endoderm, an embryonic digestive tract Mesoderm, which partly fills the space between the ectoderm and endoderm

16. Embryonic tissue layers begin to differentiate into specific tissues and organ systems after gastrulation.

18. Meanwhile, the four embryonic membranes develop into Amnion Chorion Yolk sac Allantois

19. The embryo floats in the fluid-filled amniotic cavity, while the chorion and embryonic mesoderm form the embryo�s part of the placenta

20. Embryonic induction initiates organ formation Induction is the mechanism by which one group of cells influences the development of tissues and organs from ectoderm, endoderm, and mesoderm Adjacent cells and cell layers use chemical signals to influence differentiation Chemical signals turn on a set of genes whose expression makes the receiving cells differentiate into a specific tissue

21. Pattern formation organizes the animal body Pattern formation is the emergence of a body form with structures in their correct relative positions It involves the response of genes to spatial variations of chemicals in the embryo

22. Changes in cell division, cell shape, cell migration, and programmed cell death give form to the developing animal Tissues and organs take shape in a developing embryo as a result of cell division cell shape changes cell migration

23. programmed cell death (apoptosis)

24. Morphogenesis Cell division -The orientation of the mitotic spindle determines the plane of cell division in eukaryotic cells -If spindle is centrally located, two equal-sized daughter cells will result -If spindle is off to one side, two unequal daughter cells will result

25. Morphogenesis Cell shape and size -In animals, cell differentiation is accomplished by profound changes in cell size and shape -Nerve cells develop long processes called axons -Skeletal muscles cells are large and multinucleated

26. Morphogenesis Cell death -Necrosis is accidental cell death -Apoptosis is programmed cell death -Is required for normal development in all animals -�Death program� pathway consists of: -Activator, inhibitor and apoptotic protease

28. Morphogenesis Cell migration -Cell movement involves both adhesion and loss of adhesion between cells and substrate -Cell-to-cell interactions are often mediated through cadherins -Cell-to-substrate interactions often involve complexes between integrins and the extracellular matrix (ECM)

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