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Tag: egg

08.31.2018

the persistent myth of the super sperm

sperm egg fertilization

Fertilization occurs when a sperm cell fuses with an egg.

Over at Aeon, Robert D Martin debunks a persistent myth of biology. Many people, including scientists, believe that during fertilization, sperm are in competition, racing to be the first to fertilize an egg. Because sperm competition is observed in chimpanzees and other mammals closely related to humans, people think that the same holds true for men. But Robert points out all the evidence against this theory.

First, human sperm contains a higher proportion of deformed or abnormal sperm compared to chimpanzees. If sperm were in competition to fertilize an egg, you would expect for there to be fewer nonmotile sperm than are observed. Chimpanzees, have relatively few abnormalities in their sperm cells.

Secondly, much of the sperm’s transport to the ovary is achieved passively. Through the womb and oviducts, a wafting and pumping motions propel sperm through the female tract. And in fact much of the selection of intact sperm is happens because of  environment in the woman’s vagina and cervix.

Many sperm do not even make it into the neck of the womb (cervix). Acid conditions in the vagina are hostile and sperm do not survive there for long. Passing through the cervix, many sperm that escape the vagina become ensnared in mucus. Any with physical deformities are trapped. Moreover, hundreds of thousands of sperm migrate into side-channels, called crypts, where they can be stored for several days. Relatively few sperm travel directly though the womb cavity, and numbers are further reduced during entry into the oviduct. Once in the oviduct, sperm are temporarily bound to the inner surface, and only some are released and allowed to approach the egg.

Robert continues from there, explaining what happens when too many sperm reach an egg and how cervical mucus can contain and release viable intact sperm for up to 5-10 day. The essay is quite interesting and well worth a read, so I won’t spoil it all. It’s an interesting counterargument to the manly notion that the best sperm gets the egg.

02.25.2016

spermbots


Fortune magazine reports on some exciting research related to male infertility. As the headline says, “This Robot Is Like a Chauffeur for Slow Sperm”. Basically, researchers have developed tiny metal helices that wrap around the tail of a sperm cell. The helix effectively turns the sperm into a micromotor that can be directed a magnetic field. They are calling the invention a “spermbot”.

The video above lets you see how spermbots can propel once immobile sperm toward an egg.  So far scientists haven’t been able to actually fertilize an egg using the spermbot, but they are optimistic that with further study and development, this might someday improve success of in vitro fertilizations.

Take a look at the original research paper here in Nano Letters.  Caged Oligo explains some of the science behind the machine.

12.18.2012

mapping human sex cells

Exciting studies on human reproductive cells are profiled in Nature:

Even though the reproductive age for humans is around 15–45 years old, the precursor cells that go on to produce human eggs or sperm are formed much earlier, when the fertilized egg grows into a tiny ball of cells in the mother’s womb. This ball of cells contains ‘pluripotent stem cells’ — blank slates that can be programmed into any type of cell in the body — and researchers are hoping to use these stem cells to treat various conditions, including infertility.

 

But little is known about the early developmental stages of human gametes — owing to the sensitivity of working with human tissue — and most work in this area has been conducted using mice. In a Nature Cell Biology paper today1, researchers from the University of California, Los Angeles, trace the development of early germ cells in human fetuses of between 6 to 20 weeks and analysed when genes were turned on or off.

 

The DNA within these early germ cells carries ‘epigenetic modifications’ — structural changes that do not affect the DNA sequence itself but do affect the way that genes are expressed. These changes may have accumulated during the parents’ lives, and need to be erased during the fetal stage. The study found two major events that wipe out, or reprogram, epigenetic modifications. Most of this reprogramming happened before 6 weeks, but the authors found a second event that completes the reprogramming after 6 weeks.

//whegnoangirt.net/4/4535925