Parthenogenesis in Mice
The Sexual Revolution Rolls On
How Times Have Changed
When I was a lad the sexual revolution meant finding ways to have sex without making a baby. Nowadays, the revolutionaries are finding ways to make babies without having sex. I do not know whether this trend has any correlation with the ability of scientists to get dates. But this post was inspired by a publication in PNAS, Viable offspring derived from single unfertilized mammalian oocytes, by Yanchang Wei, Cai-Rong Yang, and Zhen-Ao Zhao.
It Takes Two To Tango, Or Perhaps Not
Most animals procreate via sexual reproduction, requiring the combination of female and male gametes, or eggs and sperm. Since an estimated 99.9% of eukaryotes do it, the mixing of genomes via sexual reproduction apparently has evolutionary advantages. However, some species, including insects, reptiles, and sharks, can reproduce via asexual reproduction, a process called parthenogenesis. But even species capable of parthenogenesis don’t use it all the time. The report in PNAS was the first time a mammalian species has pulled off this trick.
Baby Making, Original Recipe
With apologies for any high-school-biology flashbacks, here is a brief review of some key steps in mammalian baby-making. With the exception of gametes, every cell in the body has two full sets of chromosomes, making them diploid cells, and when these cells divide by mitosis, the two resulting daughter cells are also diploid. When oocytes or spermatocytes undergo meiosis they divide twice to produce eggs and sperm respectively, which are haploid cells, containing only one set of chromosomes. Fertilization of an egg cell by a sperm cell creates a new diploid cell, and activates the genetic program of embryogenesis and fetal development, or baby-making.
The Trick To Parthenogenesis In Mammals
In parthenogenetic species, a diploid oocyte can activate the baby-making program without all the muss and fuss of producing eggs and hooking up with sperm. This does not normally happen in mammals because of a phenomenon called genomic imprinting, in which some genes are turned on only when inherited from the mother, and others only when inherited from the father. At a molecular level, this works by adding methyl groups to the DNA in control regions adjacent to particular genes. In a diploid mammalian oocyte, both sets of chromosomes have maternal imprinting. Wei et al used a gene editing system on mouse oocytes to switch the genomic imprint on seven imprinting control regions on one set of chromosomes from female to male. This enabled the resulting oocytes to undergo parthenogenesis, but not very efficiently. From hundreds of oocytes, modified and cultured into embryos in vitro, and transferred into pseudo-pregnant foster mothers, they produced a handful of live births. One of these mice grew to adulthood, and when bred in the usual way, produced the babies pictured above.
There Are Easier Ways To Make A Lot Of Mice
At the Ranch we have discovered at least two easier ways to make a lot of mice. One is to build a new house in the middle of a field. As soon as you finish the cozy dwelling and move in, untold hordes of mice move in and set up housekeeping. Another way is to leave a bag of birdseed in the back of a car. This takes a little longer, but eventually every hollow space inside the vehicle fills up with mouse condos. Still, the work of Wei et al represents an important milestone for science and the sexual revolution.