July 2, 2021 | Jerry Bergman

Cilia ‘Magic Carpet’ Required for Life

Small Details Can Be Critical for Life:
Another Example of Irreducible Complexity
Is Vital for Fertilization

 

 

by Jerry Bergman, PhD

Looking for evidence of  intelligent design requires looking at, not only the big picture, but also the smallest details, such as the tiny motile cilia in the female reproductive system. While denying the concept of irreducible complexity (IC), scientists continue to provide a steady flow of well documented new examples of IC. The design of the tiny motile cilia explained in this review is just one of the latest of many examples.

Motile Cilia and Fertilization

The first step in fertilization is when an egg is released from the ovary, a process called ovulation. Fertilization in eutherian mammals (all placentals excluding marsupials and monotremes) cannot occur unless the oocytes (the mother’s eggs) released by the ovary are able to enter the oviduct (or uterine tube, formally called the fallopian tube).[1] Two steps are involved in oocyte transport from the ovary to the oviduct. The first is the oocyte is picked up by the oviduct fingers called fimbria. The second is transport of the oocyte through the oviductal ampulla, as shown in the illustration below.

Figure 1. Fertilization.  Note the finger-like projections at the beginning of the oviduct called fimbria where the egg travels toward the uterus.

Figure 1. Fertilization. Note the finger-like projections at the beginning of the oviduct called fimbria where the egg travels toward the uterus.

We are alive because of a “magic carpet of fully motile cilia” that move the eggs into the oviduct toward the uterus.[2] Furthermore, as Yuan et al. demonstrate, “the carpet of tiny motile cilia that coats the lining of the infundibulum is crucial to successful oocyte pickup and transport into the oviduct.”[3] It was once thought, in contrast to this new finding, that “Although the cilia lining the tubal mucosa may also play a role in egg transport, their action is not obligatory because women with immotile cilia syndrome are often fertile.”[4]

The space between the oocyte and the oviduct at the extremity of the oviduct is a funnel-shaped cavity called the infundibulum. It is this portion of the oviduct that is responsible for capturing the oocyte when it is expelled from the ovary. The tiny motile cilia that coats the lining of the infundibulum is now recognized as far more complex and important than previous believed.

The research that determined these factors was critical was done by Yuan et al. They produced a modified strain of female mice whose oviducts were largely devoid of motile cilia. Called knockout mice because the miRNA that produce the cilia were removed, knocking out the motile cilia. The results of this study showed the cilia were essential because all “Knockout females were infertile, even though they produced normal amounts of oocytes and reproductive hormones. Their infertility resulted, instead, from a failure of oocyte pickup”[5] Yuan et al. observed that, after they had been released from the ovary, oocytes did not enter the oviducts of the knockout mice but rather accumulated in the bursal cavity outside of the oviduct.[6] Furthermore, they found in

addition to their critical role in oocyte pickup, oviductal cilia have two additional fertility-promoting functions in female mice: controlling sperm migration to the site of fertilization and transporting the embryo from the site of fertilization in the oviductal ampulla to the uterus for implantation…. both of these functions were reduced, but not eliminated, in the miR-knockout female mice.[7]

The latter was also experimentally demonstrated in hamsters. The study concluded, in

the ovary, each oocyte matures within a follicle, in which it is surrounded by supportive granulosa cells. As the time of ovulation nears, the granulosa cells close to the oocyte transform into cumulus cells, which begin secreting a hydrated elastic extracellular matrix. At ovulation, the oocyte plus its cumulus cells and their matrix—the cumulus–oocyte complex (COC)— is released from the ovary and must be pulled into the oviduct, vaulting over a gap between the surface of the ovary and the open end of the oviduct, the infundibulum. Failure of COC pickup can lead to [the] failure of sperm to fertilize the oocyte or, worse, to ectopic implantation of an embryo outside of the uterus. … Yuan et al. demonstrate that the carpet of tiny motile cilia that coats the lining of the infundibulum is crucial to successful oocyte pickup and [its] transport into the oviduct.[8]

A few knockout female mice retained some motile cilia in their oviduct, but these cilia were insufficient to support the cumulus–oocyte complex pickup and its transport. Many cilia, working in concert, were required to transport the relativity large cumulus–oocyte complex. They also concluded that specific molecules directly mediate oocyte adhesion to cilia.

The Yuan et al. findings are very relevant to human reproduction, but a significant difference in rodent and human reproduction design is the rodent ovary is encapsulated by a thin membrane (called the bursa) that was fused with the oviductal infundibulum. This membrane enabled Yuan et al. to locate and examine in the knockout mice oocytes that did not enter into the oviducts. Since women lacked the encapsulating ovarian bursa, they likely had a lowered probability of oocyte pickup, thus movement into the oviduct.

Conversely, the large fimbria surrounding the human infundibulum opening largely compensated for the bursa absence. Its’ cilia-lined fimbria effectively facilitated the movement of the oocytes closer to the oviduct. If the fimbria fail to catch the cumulus–oocyte complex, it could end up in the peritoneal cavity. If fertilized by sperm that leak out of the infundibular end of the oviduct, a life-threatening abdominal ectopic (outside-the-uterus) implantation can occur, another reason for the importance of the motile cilia.[9]

Figure 2. Another picture of Fertilization. Note the finger-like projections at the beginning of the oviduct called fimbria where the egg (oocyte) travels toward the uterus. From Wiki Commons

Evolution

The evolution of the “magic carpet of fully motile cilia” and the many other parts of the female reproduction system, is usually ignored because even just-so stories of its possible evolution have eluded Darwinists.[10] Even simple problems are a challenge to explain by evolution, not to mention how they evolved. One example: it is not clear how the two different gametes can move in opposite directions in the oviduct by cilia. The sperm move(s) in one direction by cilia towards the ovum, and the egg moves in the other direction away from the ovum by cilia.[11] Another example is the problem of how the rejection of the fetus is prevented. The embryo, which becomes the fetus, is a combination of the mother’s and father’s genes, thus is considered foreign tissue. As to this problem, “a number of explanations have been offered, none of which is [are] fully satisfactory.”[12]

Summary

The previous conclusion that “the cilia lining the tubal mucosa may also play a role in egg transport” and their action is not required for fertilization is, according to this research, not only misguided, but the opposite is true. The motile cilia are critical for fertilization and their design greatly reduces the likelihood of a dangerous, possibly lethal to the mother, ectopic pregnancy. This research indicates that most mammals require a carpet of morphologically normal ciliated cells with fully motile cilia for pickup of the cumulus–oocyte complex and its transport into the oviduct. In short, without the “tiny motile cilia,” humans, and many other animals, cannot reproduce, spelling their extinction.

References

We owe our lives to numerous programmed systems that all must work at the right time and place. (Corel Pro Photos)

[1] Suarez, Susan S., and Wolfner, Mariana F.  2021. “Cilia take the egg on a magic carpet ride.” Proceedings of the National Academy of Science U.S.A. (PNAS), July 6.

[2] Suarez and Wolfner, 2021.

[3] Yuan, Shuiqiao, et al. 2021. Oviductal motile cilia are essential for oocyte pickup but dispensable for sperm and embryo transport. Proceedings of the National Academy of Science U.S.A., June 1, 118 (22) e2102940118.

[4] Suarez, Susan. 2015. Gamete Transport. Science Direct.

[5] Suareza and Wolfner, 2021, p. 1.

[6] Suareza and Wolfner, 2021, p. 1.

[7] Suareza and Wolfner, 2021, p. 2.

[8] Suareza and Wolfner, 2021.p. 2.

[9] Trevathan, Wenda R. 2015. Human Birth: An Evolutionary Perspective. New Brunswick, NJ: Aldine Transaction.

[10] Smith, F. LaGard. 2018. Darwin’s Secret Sex Problem. Bloomington, IN: Westbow Press.

[11] Suareza and Wolfner, 2021, p. 2.

[12] Trevathan, 2015, p. 10.


Dr. Jerry Bergman has taught biology, genetics, chemistry, biochemistry, anthropology, geology, and microbiology for over 40 years at several colleges and universities including Bowling Green State University, Medical College of Ohio where he was a research associate in experimental pathology, and The University of Toledo. He is a graduate of the Medical College of Ohio, Wayne State University in Detroit, the University of Toledo, and Bowling Green State University. He has over 1,300 publications in 12 languages and 40 books and monographs. His books and textbooks that include chapters that he authored are in over 1,500 college libraries in 27 countries. So far over 80,000 copies of the 40 books and monographs that he has authored or co-authored are in print. For more articles by Dr Bergman, see his Author Profile.

(Visited 407 times, 1 visits today)

Leave a Reply