Placental Histology

Another experiment that I'm pursuing in collaboration with L~ (an undergraduate here at UM) is to analyze placental histology of hybrid hamsters. She found that there seems to be some striking abnormalities in the layering of the hybrids' placentas. Placentas are very complex and formed from three main embryonic tissue layers (labyrinthine trophoblast, spongiotrophoblast, and trophoblast giant cells) as well as a maternal layer (decidua).

***This figure is taken from Wagschal and Feil (2006) - a great paper on imprinting and the placenta***

So far L~ has found that there seems to be a sex-specific placental abnormalities in the hybrids - only the female hybrids show major disruptions of the boundaries between the layers, especially between the labyrinthine trophoblast and spongiotrophoblast. This is quite exciting as I can find nowhere in the published literature that reports sex-specific hybrid phenotypes. It also complicates the over/under-growth story because overgrowth assorts by cross type, not sex while undergrowth is only found in males, not females. If we assume that abnormal layering of the placenta results in abnormal nutrient transfer, then L~'s defects do not explain the patterns of over/under-growth.

However, the issue we have is that the sample size is quite low - 7 males and 2 females total from both hybrid types. We are now curious if the pattern that both females show abnormal morphology is true or only an artifact of small sample size. To address this, I have just set up 10 more crosses (expectation is ~50 offspring/placentas) that L~ and I will be dissecting and doing histology to next week.

I hope to be able to present the findings at the Evolution Conference in Salt Lake in a couple months.

6-4-13 update: So far I have dissected 5 Sun x Cam (overgrown) crosses and 1 Cam x Sun (undergrown) cross resulting in 10 placentas (7 Sun x Cam and 3 Cam x Sun). I fixed these in 4%PFA overnight and used the histology lab's tissue processer to embed them in parafin. Yesterday I sectioned them and put them on slides. Now I need to stain them and then measure them.  I had forgotten how difficult and touchy sectioning is. Major props to L~ for all the sectioning she did on the earlier samples.

6-18-13 update: I have dissected everything, embedded them, sectioned them, stained them, and imaged them. I'm going to present the results at Evolution this weekend and I'll type up a post afterwards.

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Wagschal, A. and R. Feil. 2006. Genomic imprinting in the placenta. Cytogenetic Genome Research 113:90–98.