26 September 2016

Greetings to the descendants

About non-classical methods of inheritance that can pass for telegony

Oleg Lischuk, N+1

Dear readers, before we begin the narrative, let's agree right away: there is no telegony. Agreed? Then we will tell you three stories about how inheritance can actually occur that is not related to the direct transmission of the genes of their parents to the descendants.

The concept of telegony is that all former sexual partners of a woman, regardless of whether she gave birth to them or not, transmit a number of their key features (external features, physique and others) to her children from subsequent men. Moreover, the first sexual partner has the greatest influence in this sense. This concept has a centuries–old history - Aristotle wrote about it. The very term "telegony" was proposed by the German evolutionary biologist August Weissmann in the XIX century (from other Greek. τῆλε - "far away" and γόνος – "birth, origin"). At first, official biology considered telegony quite seriously, but subsequent genetic studies and numerous experiments demonstrated its inconsistency.

The first confirmed story

You can get DNA in your body, in addition to inheriting it from your parents, as a result of microchimerism. This is the name of a phenomenon in which a placental mammal, including a human, has a small number of cells or genetic material of another individual of the same species.

The most common type of microchimerism is the exchange of cells between mother and fetus during pregnancy. Although the placenta as a whole does not allow direct contact of maternal and fetal blood, a small number of cells still pass through it. In some cases, these cells can form stable lines that remain viable in someone else's body decades after birth, or even throughout life. Such fetal lines in the mother can be represented by immune, mesenchymal stem or placental cells, and maternal in the child – as a rule, only leukocytes. Due to the peculiarities of the structure of the placenta, a woman receives fetal cells more often and in greater numbers than vice versa. There is also evidence that the cells of the embryo can penetrate into the mother's body even before the formation of the placenta – at the stage of its implantation into the epithelium of the uterus.

In most cases, the search for male genetic material in women is used to diagnose microchimerism. Not because the male fetus often transfers its cells to the mother, it's just that it's much easier to detect a sexual Y chromosome that is not typical of a woman. At the same time, male cells or genetic material were found both in women who did not give birth to sons, and in women who never gave birth at all. Such a phenomenon can be a consequence of previous artificial or spontaneous abortion, as well as unrecognized miscarriage in the case of pregnancy with a male embryo in the early stages.

There are other mechanisms for the occurrence of microchimerism. So, a woman who has the cells of her mother or a child born earlier can "share" them with subsequent children. These children, in turn, can pass them on to their descendants. Another option is the receipt of microchimeric cells by a mother and child from an undeveloped twin (it happens that the development of one of the twins stops in the early stages and it remains unnoticed). Much less often, microchimerism can occur as a result of medical manipulations, such as blood transfusion.

The ingestion of cells of previous children into the body of subsequent ones. Amy M. Boddy et al., BioEssays, 2015

Microchimerism occurs in animals with all four types of placenta – it has been observed, for example, in primates, dogs, cows and mice. In cattle, most twins are microchimers, since their placentas tend to merge, which leads to an interchange of blood. If such twins are of separate sexes, the females, under the influence of the twin brother's sex hormones, lose the ability to reproduce and do not bring milk. Such animals are called freemartins.

Microchimeric cells can occur in almost any organs and tissues, including the brain (most often in the blood, skin, glands and internal organs). The physiological role of this phenomenon is still practically unknown – scientific studies of microchimerism have been conducted for only a few decades. It is believed that it can have both positive and negative effects.

According to available data, microchimerism can play a significant role in the development of the immunity of the unborn child and the receipt of nutrients through the placenta and with breast milk. There are indications that microchimerism can improve the regeneration (recovery) processes of various damaged tissues, as well as facilitate the course of rheumatoid arthritis during pregnancy and protect against certain types of cancer.

At the same time, observations show that the presence of foreign cells may underlie the development of systemic scleroderma and some other autoimmune diseases, such as autoimmune thyroiditis, systemic lupus erythematosus and others (this is supported by the high prevalence of these diseases in women over 40 years old, that is, those who gave birth). It is also most likely involved in the development of a number of malignant neoplasms and may affect the survival of organs during transplantation.

Current and future studies should accurately determine the role of microchimerism in maintaining health and the development of diseases. However, it is safe to say that he cannot influence the fundamental innate signs, such as appearance, physique and hereditary material of germ cells.

If microchimerism is widespread (according to available data, microchimers can be up to 75 percent of women who have given birth and a significant proportion of other people), then the other two stories relate only to isolated observations, and not in mammals.

The second story, mysterious

In 2015, the Sorbonne staff discovered that the urban pigeon (Columba livia) has a specific immunity that can be inherited through a generation. As is known, the mothers of all vertebrates "train" their immunity by transmitting their specific maternal antibodies (MatAb) to them. However, there was no data on the transfer of such information to grandchildren.

To find out the fundamental possibility of such a phenomenon, French scientists twice injected 60 female pigeons with KLH protein (keyhole limpet haemocyanin, fissurella hemocyanin) as an antigen, which serves as an oxygen carrier in the sea snail Megathura crenulata. This high-molecular metalloprotein is known for its high immunogenicity in vertebrates, which does not harm their health. Pigeons could not contact him in any way, which excluded the production of antibodies to KLH in a natural way.

The next two generations of female pigeons were injected with protein-antigen at the age of 21 and 35 days. Along the way, the researchers monitored the dynamics of the production of antibodies to it.

The level of antibodies against the KHL antigen in the blood of pigeons-"granddaughters" whose "grandmothers" 
were (black) or were not (white) immunized. 
A. Ismail et al., Biology Letters, 2015

It turned out that the introduction of KLH to female pigeons of the first generation did not affect the immune response of their "daughters" in any way. But in "granddaughters" the level of antibodies to this protein increased with age, which was not observed in birds with non-immunized "grandmothers". At the same time, no significant amount of anti-KLH antibodies was observed in the egg whites from which they appeared.

The mechanism of this phenomenon, as well as its presence in other animals, including humans, remains unclear, but it is clearly not related to the known mechanisms of inheritance.

The third story, dubious

And finally, the signs of "real" telegony were observed in flies of the species Telostylinus angusticollis by researchers from the University of New South Wales in Sydney. To find out the possibility of this phenomenon, they raised insect larvae on nutrient-poor and nutrient-rich environments. As a result, the flies hatched from these larvae had a significant difference in body size.

After that, the scientists twice crossed large females, whose larvae grew on an enriched nutrient medium, with males of different sizes. The first crossing was carried out before their puberty, and, as scientists write, the sperm of these males had to die, although they do not provide evidence of this. Three weeks later, the females were re-crossed with both types of males. As a result, there were four combinations of crosses according to the size of males: large-large, small-small, small-large and large-small.

Multivariate statistical analysis of the size of the offspring showed that it depends on the size of the male with whom the fly mated first, and the size of the second sexual partner practically does not affect it.

To exclude the possibility of behavioral regulation of the size of the offspring depending on the appearance of the first male (who knows what these flies are capable of), immature females were placed in the same container with males of a certain size, but they were not allowed to interbreed. Crossing with the second male was carried out in the same way as in the first experiment.

It turned out that the size of the first male affects the fatness of the offspring only if his sperm enters the female's body. From this, scientists concluded that the seminal fluid of flies may contain some kind of non-genetic factor that can affect the subsequent offspring of females, but they did not search for this factor.

In response to a request from N+1, a member of the research team, Angela Crean, said that the search for an unknown factor is underway and "several promising areas for study have already been identified, but no final results have been received yet." She refused to give more detailed information before the publication of the results.

Krin also mentioned that another team found the influence of non-breeding males on offspring in fruit flies of Drosophila (Drosophila melanogaster). However, these works are practically unrelated – in the aforementioned study with fruit flies, it was shown that crossing females with sterile males made their female offspring more fertile, that is, its influence was manifested only in the next generation. As the authors themselves note, this is most likely due to the receipt by first-generation females of additional seminal fluid proteins, the effect of which on the fertility of their "daughters" has been shown in previous studies.

The work of Australians has a number of weaknesses. Firstly, the sample under study was very small - only 24 females, which makes their influence on the results very strong. Secondly, the experiments were carried out not on pure insect lines, as is customary in genetic research, but on wild flies. And thirdly, the influence of the size of the first male on the size of the offspring did not exceed half the standard deviation, that is, if it exists, it cannot be called significant in any way. 

The effect of the body size of the first and second male on the body size of the offspring.
On the ordinate axis is the standard deviation from the mean.
Angela Crean et al., Ecology Letters, 2015

Let's see if we can reproduce the results obtained in a larger number of insects or in their other species, as well as find the same non-genetic factor in sperm. Until then, it is not possible to talk about reliable detection of telegony, even in flies.

However, it is obvious that non-classical methods of inheritance nevertheless exist and, perhaps, some of them remain unknown. But the degree of their significance will be very limited, since all the main signs of offspring are due to the genes of their biological parents, which has long been confirmed by qualitative scientific research.

Portal "Eternal youth" http://vechnayamolodost.ru 26.09.2016

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