Wednesday, 13 September 2017

Marsupial and eutherian placentation

Placenta of the tammar wallaby showing the bilaminar (BOM)
and trilaminar (TOM) omphalopleure. From Guernsey et al.
eLife 2017 CC The Authors

A brand new paper compares the transcriptomes of marsupial (tammar) and eutherian (mouse and human) placentas and mammary glands (here). It confirms that marsupials have fully functional placentas expressing many of the same genes as eutherian ones.

There is evidence for a division of function between the two parts of the yolk sac placenta, with the nonvascular part (BOM) being responsible for uptake and metabolism of nutrients and the vascular part (TOM) for respiration. I am not sure how much oxygen the tiny marsupial embryo needs. Perhaps the TOM is more important for removing CO2 and regulating the acid-base balance of the embryo. The tammar has an embryonic-type hemoglobin more capable of sequestering oxygen (protecting the embryo from reactive oxygen species) than transporting it to tissues.

A fascinating detail is that the yolk sac endoderm of the tammar has assumed functions, especially to do with trafficking of nutrients, that in eutherians are served by trophoblast.

Genes expressed in mammary gland and placenta
of marsupials and eutherians. From Guernsey et al.
eLife 2017 CC The Authors
Because much of development in the wallaby is supported by lactation, it is interesting to find considerable overlap in the transcriptomes of marsupial mammary gland and eutherian placenta.

My only criticism of this paper would be: the mouse has a yolk sac that supports early embryonic development and continues to function alongside the placenta right up to term. Perhaps the authors could not identify a data set on mouse yolk sac transcriptome, but they should have referenced the eutherian yolk sac in their discussion. An interesting theory by Claudia Freyer et al. (here) is that the stem species of therians (marsupials and eutherians) had both types of placentation.
For additional remarks on this paper see Nature News and Comments (here).

Monday, 4 September 2017

Hermann von Ihering and polyembryony in armadillos

Uterus of the mulita (Dasypus hybridus) with 9 identical
embryos. From Fernandez Morph Jahrb 1909; 39:302-333
In 1886 Hermann von Ihering opened the uteri of two pregnant armadillos. Both contained 9 fetuses of the same sex. Each fetus had its own amnion but all were enclosed in a common chorion (placenta). He was the first to propose that the embryos were derived from a single fertilized egg with splitting into separate embryos occurring early in development.
Arrangement of fetal membranes in the mulita (Dasypus hybridus).
From Fernandez Morph Jahrb 1909; 39:302-333
Ihering had studied the mulita or Southern Long-Nosed Armadillo (Dasypus hybridus). Later Fern├índez demonstrated that splitting occurred at the embryonic shield stage in the mulita. Newman & Patterson, working with the nine-banded armadillo (D. novemcinctus), came to a similar conclusion. Fern├índez, however, was the first to obtain early stages before splitting occurred. More recently, the nine-banded armadillo was the object of elegant studies by Allen Enders (summarized here). Specific polyembryony is known only from Dasypodinae and is thought not to occur in the two other subfamilies of armadillo.
Hermann von Ihering (1850-1930)
CC BY-SA 3.0 Wikimedia Commons
Hermann von Ihering was a German zoologist who relocated to Brazil in reaction to his family's disapproval of his marriage to a widow with a child. This was in 1880. His first years were spent as a collector in the southern state of Rio Grande do Sul, based on an Island known as Ilha do Doutor (Doctor's Island). In 1893 he became the first director of Museu Paulista (State Museum of Sao Paulo) and held this post for 23 years.

Hermann von Ihering´s principal area of expertise was mollusks. He also became an expert on the birds of the State of Sao Paulo, of which he observed 695 species and subspecies. For my Brazilian readers there is an excellent recent biography by Hitoshi Nomura (open access here). It lists 338 of his publications.

His son Rodolpho von Ihering (1883-1939) was also a zoologist. He was appointed vice director of Museu Paulista, which led to the accusation of nepotism that was to force Hermann's resignation. Rodolpho was an expert on fish and is credited with founding Brazilian pisciculture with stations at Porto Alegre in Rio Grande do Sul and Pirassununga, S.P.

References: Biol Zentralblatt 1886; 6:532-9 and Arch Physiol 1886; pp. 443-50