No sperm is the same

Unique sperm: no sperm is the same

07/23/2012

All sperm are unique. This has been discovered by US researchers at Stanford University using a novel method for genome sequencing. Like Stephen Quake and colleagues in the trade magazine „Cell“ report, distinguish the sperm of a man - despite externally identical appearance - in their genes.

According to the scientists, the examined sperm showed different compositions of the genetic material. The combination of chromosomes was highly variable from sperm to sperm. In some cases, the sperm even showed new mutations, according to Quake and colleagues in the journal „Cell“. For the first time, researchers have succeeded in using their new method to study the complete genome of each sperm.

Special procedure allows sperm genome sequencing
To analyze the genome of sperm, the researchers constructed a so-called „Microfluidic system“, which is equipped with 48 miniature reaction chambers and numerous connecting lines with tiny diameter. By pumping the sperm are distributed in the apparatus so that at the end of exactly one sperm in each second chamber ends up. The researchers were then able to extract and duplicate this in order to sequence the genome. For this form of „High-density genotyping“ According to the researchers, they use 91 sperm from a 40-year-old European male whose genetic material has been previously sequenced and extensively studied. The offspring of the subject were healthy and his sperm showed in the medical analysis no unusual peculiarities.

Different combination of chromosomes
When investigating the sperm cell, Stanford University geneticists found spermatozoids to be distinctly different in their combination of chromosomes and the location of each DNA segment. In addition, there were mutations that caused significant differences between the genetic information of sperm. It was particularly noticeable that in some sperm some chromosomes were completely absent while in other combinations that were theoretically excluded. For example, some sperm cells simultaneously contained an X and a Y chromosome. In the analysis of the genetic information from the 91 sperm discovered the researchers numerous others „error“. For example, sperm number 60 did not have chromosome 8 and sperm number 64 lacked chromosomes 6, 11, 19 and 22. Also, two spermatozoa lacked larger portions of chromosome 13, which, according to the researchers, increased the risk of skulls Associated with malformations. For sperm number 63, however, the scientists were able to detect both an X and a Y chromosome simultaneously. Sperm number 59 shows the attachment for several Y chromosomes, according to Quake and colleagues.

Wrong number of chromosomes in some sperm cells
According to the US scientists, the male organism in sperm production is constantly putting together new combinations of hereditary factors in order to increase the adaptability of the offspring through the genetic variations. The fact that some sperm cells contain the wrong number of chromosomes is, according to the experts by no means unusual. This genetic peculiarity is referred to as aneuploidy and is found in about 20 to 30 percent of female eggs, Quake and colleagues report. One of the known disorders based on aneuploidy is, for example, trisomy 21 (Down syndrome). In terms of sperm, the percentage of aneuploidy detected is between two and ten percent according to the US researchers.

New method of genome sequencing also applicable to other cells?
The sperm genome sequencing method used by the scientists is also believed to be useful in the analysis of other cells. For example, the method would probably also be applicable to the genetic analysis of various cells from a tumor to study commonality in the mutations, write Stephen Quake and colleagues. (Fp)

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Image: Thommy Weiss