The Stages Of Embryonic Development After Fertilization

920 Words4 Pages
225BMS Coursework Questions

1. Briefly describe the four main stages of embryonic development after fertilization.
[5 marks]
100 words

During cleavage the zygote experiences rapid mitotic divisions followed by cellular differentiation leading to development of an embryo. (Coventry University, 2015)

Patterning is when identical cells develop and function. Ectoderm which forms the skin, hair, nervous system epithelium and sweat glands. Mesoderm forms the muscles and connective tissues and finally endoderm which forms the digestive and respiratory organs. (Coventry University, 2015)

In differentiation the cells differentiate forming the specialised structures and functions. They form neurons, blood cells, skin cells, muscle cells etc.
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The changes that occur in the niche are more important than in stem cells themselves when it comes to the failure of stem cell activity with aging. (Fowler, 2012)

Haematopoietic stem cells (HSC) regulate the turnover of platelets, erythrocytes and all immune cells by changing between self-renewal and differentiation to a variety of specialised cells. Osteoblasts has a major role of secretion of mineralized bone matrix proteins and cells of the osteoblast lineage regulating osteoclast differentiation. (Purton & Scadden, 2008)

WNT signalling has a role in HSC regulation. Osteoblast-specific overexpression of the WNT inhibitor dickkopfhomolog 1 leads to impairment of HSC self-renewal.
The expression of Notch1 and Notch2 in HSCs is shown to be important for their response to endothelial – derived maintenance factor.
Hedgehog signalling can cause the HSC expansion through the activation of bone morphogenetic protein signalling pathways (Celso and Scadden 2011).

The JAK-STAT pathway also regulates haematopoiesis in Drosophila. This pathway is a common mechanism for niche signalling in somatic tissues. BMP signalling is required for the maintenance of ES cells (Agosto, et al., 2007)


3. ES and iPS cells are both pluripotent stem cells but are obtained in different ways. Describe how both are obtained.
[10 marks]
200 words

Embryonic stem cells (ESCs) are grown in the laboratory from cells found in the early embryo. ESCs have an unlimited chance to
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