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I found this paragraph in my study materials about implantation

Original

Simplest trophoblast excretes trypsin related substances and embedding consists of 3 stages:

  1. The blastocyst (composed of cytotrophoblast and embryoblast) stick to the uterine wall
  2. Enzymes digest nische (little hole in the endometrium) to the functional layer and the blastocyst deepens in it. The nische is a closed and destroyed functional layer, in it tissue and blood is used for trophic (called a nischtrophic way of feeding)
  3. Implantation ends in 13½ day when the functional layer covers the blastocyst. Implantation normally takes place in anterior and posterior wall of uterus, sometimes in superior or fundus wall.

My suggestion for corrections

Syncitiotrophoblast excretes Digestive Enzymes and embedding consists of 3 stages:

  1. The blastocyst (composed of cytotrophoblast and embryoblast) stick to the uterine wall
  2. Syncytiotrophoblast expresses digestive enzymes which dig a little hole (nische) into endometrium. The hole is usually filled with maternal tissue (so closed) and blood used by the conceptus for histotrophic feeding (nischtrophic way of feeding)
  3. Implantation should end in 13½ day when the endometrium covers the blastocyst. Implantation normally takes place in anterior and posterior wall of uterus between glands of the hypertrophic endometrium, sometimes in superior or fundus wall.

I cannot accept the phrase simplest trophoblast and the use of the words trypsin related substances. Really, how can you get trypsin without pancreas? I would not use the word trypsin although the enzymes may have some structural similarities.

How would you reformulate the paragraph?

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    $\begingroup$ If you think about what the trophoblast (particularly syncytiotrophoblast) is doing during implantation, then secreting trypsin related substances makes sense. $\endgroup$ – kmm Feb 1 '14 at 23:43
  • $\begingroup$ @kmm Can you call this trophoblast also simplest trophoblast? Where does the name come from? $\endgroup$ – Léo Léopold Hertz 준영 Feb 2 '14 at 7:07
  • $\begingroup$ Maybe it's just referring to the undifferentiated trophobast (before cytotriphoblast and syncytiotrophoblast can be identified as such). $\endgroup$ – kmm Feb 2 '14 at 15:05
  • $\begingroup$ @kmm I made big changes to the paragraph after getting the opinion of another group of students. I tried to fix it so well as I could in the my suggestion. $\endgroup$ – Léo Léopold Hertz 준영 Feb 2 '14 at 17:50
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I have no idea what is meant by 'the simplest trophoblast'. I did, however, find this review, pointing to a role of proteases in the implantation process:

Salamonsen L.A. Salamonsen and Nie, G. (2002) Proteases at the Endometrial–Trophoblast Interface: Their Role in Implantation. Reviews in Endocrine and Metabolic Disorders, 3:133-143

which discusses the roles in implantation of three classes of proteases : matrix metalloproteinases, serine proteinases and cystein proteinases. The reference to 'trypsin-like' presumably relates to the serine proteases. The review reports the results of a number of gene knockout experiments in mice in which genes for individual proteases have been disrupted which indicate that no single enzyme is identified as being essential.

Referring to

Afonso S et al (1997) The expression and function of cystatin C and cathepsin B and cathepsin L during mouse embryo implantation and placentation. Development 124:3415-3425.

the authors of the review state that:

[they] demonstrated that cysteine proteases play a critical role in implantation. Cathepsin B mRNA was expressed by mouse trophoblast throughout the invasive period (days 5.5±10.5) while the proteins for cathepsins B and L were localized to the mature invasive trophoblast giant cells; activity of these enzymes was also demonstrated. Cathepsin L was also present within the stroma particularly in the lateral decidualizing zone. Cystatin C, the major inhibitor of cathepsins, was shown to be a major product of the adjacent decidualizing stroma close to the embryo, suggesting a restraining role. After the completion of placental trophoblast invasion (day 11.5) the trophoblast cells express high levels of cystatin C, probably in association with a switch from an invasive cell type to one providing nutrients to the conceptus [35]. In addition, treatment of pregnant mice with E-64, a synthetic cysteine protease inhibitor, resulted in failure of implantation and normal uterine decidualization.

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  • $\begingroup$ You are completely right. I think the simplest trophoblast is mistake and the original author meant syncytiotrophoblast. Those enzymes secreted are structurally trypsin related. However, I would never call them such only. The best way to start would be to say digestive enzymes such as trypsinase digging a hole into the endometrium. $\endgroup$ – Léo Léopold Hertz 준영 Feb 2 '14 at 17:52
  • $\begingroup$ Perona and Wassarman (ncbi.nlm.nih.gov/pubmed/3514318) showed that a 'trypsin-like proteinase' (strypsin) is required to hatch the blastocyst and that it is concentrated on the wall-side cells of the blastocyst. $\endgroup$ – kmm Feb 2 '14 at 17:58

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