Pre-Implantation Embryo Development

Question 1

list the key developmental stages that occur before embryo implantation

Answer 1

1 - activation of embryonic genome
2 - cell divisions of zygote to form 2-cell and multicellular embryos
3 - formation of morula
4 - formation of blastocyst
5 - blastocyst hatching

Question 2

[1. activation of embryonic genome] when does zygotic genome activation occur

Answer 2

soon after fertilisation

Question 3

[1. activation of embryonic genome] what happens to epigenetic marks on DNA from parents & what does it allow

Answer 3

• most epigenetic marks on DNA from maternal and paternal genomes are cleared
• allows cells of early embryo to express all genes (ie/ early embryo cells are pluripotent)

Question 4

[1. activation of embryonic genome] in mammals by what time is zygotic genome activation complete

Answer 4

• by time 2-cell embryo forms
• embryo begins make new RNA transcripts

Question 5

[1. activation of embryonic genome] what occurs faster for paternal genome than for maternally-derived DNA

Answer 5

epigenetic reprogramming to clear DNA methylation

Question 6

[2. cell divisions of zygote to form 2-cell and multicellular embryos] when does initial division of zygote to 2-cell embryo occur

Answer 6

~30hrs after fertilisation

Question 7

[2. cell divisions of zygote to form 2-cell and multicellular embryos] in early stages of cell division, cells remain _____ & _______

Answer 7

• distinct
• pluripotent

Question 8

[2. cell divisions of zygote to form 2-cell and multicellular embryos] what does it mean by cells are pluripotent

Answer 8

• able to form any cell type in the developing embryo

Question 9

[2. cell divisions of zygote to form 2-cell and multicellular embryos] early cell cleavage occurs with major changes in embryo size - T or F

Answer 9

False

Question 10

[2. cell divisions of zygote to form 2-cell and multicellular embryos] what does early cell cleavage occur within

Answer 10

zona pellucida

Question 11

[3. formation of morula] how does cell compaction occur & what does this lead to

Answer 11

• through fusion of cell membranes
• leads to individual cells no longer being visible

Question 12

[3. formation of morula] this is the first stage of cell development where some cell are ______ and others ___
what is the implication of this

Answer 12

• inside & outside
• exposure to different environmental signals -> lead to different expression of transcription factors => important for cell differentiation

Question 13

[4. formation of blastocyst] describe blastocyst stage of embryo structure

Answer 13

• outermost single layer of trophectoderm cells - which will form majority of placenta (foetal part)
• enclose a fluid-filled cavity
• contain inner cell mass of embryoblast cells - contains cluster of cells that will develop into embryo / foetus

Question 14

[5. blastocyst hatching] what needs to happen before a blastocyst can implant or grow further

Answer 14

blastocyst needs to hatch from zona pellucida

Question 15

[5. blastocyst hatching] at what point does blastocyst hatch from zona pellucida

Answer 15

~6-7 days after fertilisation in vivo

Question 16

[5. blastocyst hatching] describe how blastocyst is able to hatch from zona pellucida

Answer 16

• active process
• likely involves both: mechanical pressure from expanding blastocyst & secretion of enzymes to weaken glycoprotein structure of zona pellucida