The photo shows the spots I'm asking about. It is uterine horn cut along and laid flat; what you see is inside of the horn. I do surgical embryo transfer of genetically modified (microinjected) mouse embryos (at 1 or 2 cell stage). As most of the constructs are new, we expect that it may affect birth rate. In case there are no or very low number of pups born we try to investigate at what stage the problem occurs. I dissect the embryo recipients on day 21(+48 hrs to make sure that we don't sacrifice a mouse that is late to litter down). Sometimes I find dark, gelly, regularly interspaced structures on the mesenterial side of the uterus. Initially, I thought them to be implantation sites of the embryos that have been subsequently resorbed for some reason. Until I found similar structures in mice that haven't been mated with male. My question is: are there anatomically predefined sites in an uterus that embryos can invade? Are my dissections just a waste of time and yield no valuable data?

  • $\begingroup$ I haven't been able to verify this, but if the gelly on the outside of the uterus looks at all like endometrial tissue, might you be seeing mice with endometriosis? In humans, there are no special implanttation sites, just highly probable to low probability. The embryo can implant anywhere it "touches down". Where it implants does influence the probability of carrying to term, though. $\endgroup$ – anongoodnurse Sep 1 '17 at 22:38
  • $\begingroup$ Hi, It is inside the uterine horn's wall, where placentas are formed. It seems to be connected to the blood vessel branches. Basically it looks very structured and be there for the purpose. I dissected one of this thinghs and it looks (100x magnification) like very dense capillary network. $\endgroup$ – Fosfo Di Estraza Sep 2 '17 at 10:41
  • $\begingroup$ Ah, thanks. I know of no similar anatomical structures in humans. It's strange, though, that you find them only on some female mice (is that correct?) I, too, in your place would have thought them influenced by the embryo(s), since the embryo has the ability to alter the architecture of it's implantation site, especially with regard to vascularization. Odd to find them on non-mated mice. I wish I could help. $\endgroup$ – anongoodnurse Sep 2 '17 at 15:43
  • $\begingroup$ Just had a thought; when you find them in unmated mice, look at the ovaries for visible corpus lutea. It may be anatomically normal but cyclical. $\endgroup$ – anongoodnurse Sep 2 '17 at 23:40
  • $\begingroup$ I started to believe that it is anatomical feature. The problem is that I talked to many people including vet surgeon, people doing research on embryology etc and nobody gave me the clear answer. $\endgroup$ – Fosfo Di Estraza Sep 3 '17 at 12:59

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