Question

Refer to “Chromatin dynamics in the regulation of cell fate allocation during early embryogenesis” paper (found by googling), and answer the following questions.

1. At what specific stage do blastocysts start to exhibit asymmetry? Are cells at this stage still totipotent?  Why or why not?

2. Which transcription factors does trophoectoderm express?  

3. Which transcription factors do the inner cell mass express?  

4. Of the inner cell mass transcription factors, which of these is a “maternal effect gene”?  

5. When examining the organization of chromatin, what does the notation H4K20me3 mean?

6. Is DNA more or less tightly packed by H3K9me3 in heterchromatin?

7. At what stage are chromocenters formed?  What are chromocenters?  What specific types of structures do the authors think they are involved in forming?

8. What is somatic cell nuclear transfer?

Definite thumbs up for answers to these questions! Thank you!

Answer 1

Answer:             This question i have to pointswise,because of it's easy to understand you........

1) :

• Blastocyst asymmetry can be seen in the morula stage (16-cell stage), whereby the inner blastomeres arise that will later be enveloped by outer blastomeres.
• Totipotency is diminished at this stage and pluripotency starts. At 16 cell stage cells generate inner and outer cells.
• Inner cells tend to become the pluripotent inner cell mass (ICM) cells in the early blastocyst, and outer cells become the trophectoderm. You can see this in figure 1 in the above mentioned article.

2) :

• The trophectoderm expresses transcription factors, such as CDX2 (caudal type homeobox 2) and TEA domain family member 4 (TEAD4; also known as TEF3), that are restricted to, and required for, its formation or differentiation.

3) :

• Inner cell mass (ICM) expresses transcription factors such as OCT4 and NANOG.
• The transcription factors NANOG and OCT4 are not required for the initial lineage establishment between inner and outer cells of the early blastocyst and undergo complete restriction only after the subsequent lineage segregation into epiblast and primitive endoderm.

4) :

• OCT4 is the maternal effect gene in the transcription factors expressed by ICM and is important for zygotic genome activation.
• It has a very good role in the pluripotency induction and totipotency development.

5) :

• H4K20me3 (‘me’ means ‘methylation’) is a heterochromatin which represses the histone modification present in the two cell stage.
• They removed during embryonic development because of the chromatin reprogramming.

6) :

• DNA is tightly packed in H3K9me3 heterochromatin.

7) :

• Chromocenters are bundle of heterochromatin contains tightly packed protein and DNA. They are formed during interphase of cell cycle and are formed pericentromeric heterochromatin and cenpA which contains repetitive DNA.

8) :

• Somatic cell nuclear transfer (SCNT) consists of transferring a nucleus from a differentiated cell into a de differentiated cell to induce cellular reprogramming of the donor nucleus to a more plastic state.
• SCNT enables the creation of an embryo from the nucleus of an adult cell, demonstrating that the potential for totipotency is not lost in most adult cell types.

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