Exception to genetic inheritance: a worm transmits a biological trait through memory, not genes

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For most organisms, genetic inheritance is the reason why offspring look like their parents. However, there is one exception to the rule – and two teams investigated a case where a biological trait was transferred not by genes but by a memory mechanism.

Two research groups from the University of Geneva (UNIGE) in Switzerland are studying the places of centromeres – DNA sequences specialized in a chromosome which plays an important role in cell division. They discovered that in species of worms Caenorhabidite elegans – a live freely, transparent nematode only 1 mm long on average – the location of the centromere is transmitted not by genetic inheritance but by something that researchers describe as “epigenetic memory mechanism. “

Their conclusions on this exception appear in the last PLOS Biology, in a report entitled “Transgenerational legacy of centromere identity requires CENP-A N-terminal tail in C. elegans maternal germ line. “

(Photo: Genome.gov Going through Wikimedia Communal room)

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Understand the transmission mechanisms of biological characters

The passage of a biological trait occurs in living organisms – from the largest mammals to the smallest microbes – and includes physical and even behavioral traits passed down from parents to offspring. This process is known as genetic inheritance, and The cell: a molecular approach (2nd Editing) explains it as the transmission of genetic information that specifies the structure and function of a parent organism. This is usually mediated by DNA, more specifically replication in each of the cell division processes which copies the gene containing a specific composition or predisposition.

However, there are cases where a biological trait is passed down to offspring without going through the processes of genetic inheritance, and these are called epigenetic phenomena. This particular case was observed by the UNIGE researchers examining the physical separation of chromosomes into two daughter cells during cell division. A team, led by the teacher Florian Steiner of the Department of Molecular Biology, who is also the latest author of the study, looks at centromeres in the nematode C. elegans. They noted how certain chromosomal structures act as “anchors” for the memory mechanism that leads to the correct distribution of chromosomes to daughter cells. More importantly, a failure in this distribution could lead to cell death and has been observed in the development of cancer cells.

“The study of these processes is greatly facilitated in C. elegans, because this little worm is transparent and allows direct observation of cell divisions and the fate of chromosomes from one generation to the next ”, explains Reinier Proseus, first author of the study and researcher of the Department of Molecular Biology, in a press article from the University of Geneva.

Memories help determine physiological development

The other group, led by UNIGE Faculty of Medicine professor Monica Gotta also analyzes the protein that defines the placement of the centromeres on C. elegans chromosome with Steiner’s team. Their collaborative effort led to the discovery of how the protein navigates to the right location – through a specific region that “guides” the protein.

The researchers then created a mutation in the nematode in which the DNA does not have the necessary codes to “guide” the protein. Steiner explains that they initially predicted that the mutant would not be viable since the position of the centromeres could not be located since the DNA region was deleted. However, the protein still managed to reposition itself and remain functional. This led the researchers to discover that once the centromeres are properly defined from the parent, it is passed down to the offspring through cells “remembering” that particular configuration, even without the DNA codes that are believed to guide the chromosomal structures.

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