2023-09-20 15:11:40
An evolutionary trait of humans and most animals is that they inherit the mitochondrial DNA exclusively from the mother, even though the father’s sperm have mitochondria. Why then do they not transmit mitochondrial DNA?
The answer is that they don’t have it, according to the study published in Nature Genetics researchers from the Barcelona Biomedical Research Institute (IIBB-CSIC-IDIBAPS) and various centers in the United States.
The results show that sperm do not have a single complete molecule of mitochondrial DNA, nor the transcription factor TFAM necessary for their replication.
After several years of research, the authors have been able to demonstrate that sperm lack this type of DNA and, furthermore, their mitochondria do not present a mitochondrial transcription factor A (o TFAMof English Transcription Factor A mitocondrial) which is essential for human mitochondrial DNA to replicate.
“In many species, including humans, the mitochondria of the sperm are introduced into the egg during fertilization, so one of the existing hypotheses was that the mitochondrial DNA did reach the oocyte but was eliminated in the fertilization process,” he explains. the co-author Ramon Trullasresearcher at the IIBB and the Network Biomedical Research Center for Neurodegenerative Diseases (CIBERNED).
Spanish technique and Oregon samples
To find out if sperm have mitochondrial DNA, scientists at the Barcelona Biomedical Research Institute have developed a technique of PCR digital, more precise than conventional PCR and which allows the absolute number of DNA in different types of cells to be quantified in the same sample. The analyzes have been carried out with samples from clinics in Oregon (USA).
The results show that the sperm do not have a single complete molecule of mitochondrial DNA, and that the ADN mitocondrial residual found is probably not even sperm.
“Each sperm contains between 50 and 70 mitochondria, which correspond to less than 0.01 molecules of mitochondrial DNA. Although extremely low, this figure would probably be explained by a few cells that contaminated the samples (specifically leukocytes),” the authors explain in the work.
The team has discovered that what explains the absence of DNA in the mitochondria of the sperm is a process of relocalization of the transcription factor TFAM, a molecule that penetrates the mitochondria for the replication of mitochondrial DNA.
During spermatogenesis, the sperm directs the TFAM factor to the nucleus, not to the mitochondria, thus preventing mitochondrial DNA replication.
During the spermatogenesisthe sperm modifies the TFAM localization signal and does not allow it to penetrate the mitochondria but directs it to the nucleus of the sperm, which prevents the replication of mitochondrial DNA.
“Our work demonstrates that the modification of TFAM during spermatogenesis results in the elimination of mitochondrial DNA and explains its maternal inheritance. A fascinating process, a product of evolution, that prevents the inheritance of paternal DNA,” he adds. Trulling.
Our work demonstrates that the modification of TFAM during spermatogenesis results in the elimination of mitochondrial DNA and explains its maternal inheritance
Ramón Trullás (IIBB-CSIC)
This discovery of TFAm relocalization has important implications for the fields of human fertility and the germ cell therapysince it could explain some cases of oligospermia and oligoasthenospermia, an alteration in which there is a low count and low mobility of sperm.
In fact, high levels of mitochondrial DNA have been found in the sperm of infertile men with severe oligoasthenospermia, recall the authors, mostly from Thomas Jefferson University and Oregon Health & Science University in the United States.
Reference:
William Lee et al. “Molecular basis for maternal inheritance of human mitochondrial DNA”. Nature Genetics2023.
Rights: Creative Commons.
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