No, the haploid hydatidiform mole, isn’t an grotesque species (like the star-nosed mole pictured abover), or a bizarre mammalian model with asexual reproduction (like parthenogenesis in whip-tail lizards).

Rather haploid hydatidiform mole is the tissue that develops when a sperm fertilizes an egg that has lost it’s DNA, and the sperm duplicates its own genome. Tragically, due to epigenetic differences between male and female DNA, it results in a growing mass of tissue, with vesicular chorionic villi, and no discernable fetal or embryonic development. On ultrasound it resembles a cluster of grapes, and it almost always ends in spontaneous abortion. In some cases, these moles can cause choriocarcinoma (cancer of the placenta), so if detected it is treated immediately by evacuating the uterus.

Haploid Hydatidiform Mole Research to Discover New Genes

From this human tragedy, we can learn a lot about the genome, specifically about families of duplicated genes that share most of their sequence. Using conventional methods, it can be difficult to distinguish very similar genes from separate alleles at the same loci. Sequencing the moles is advantageous since they are haploid and therefore contain only one allele at each loci. Discovering recently duplicated genes that separate us from apes is of huge importance as they are a primary source of evolutionary advances and human-specific duplications may help explain the evolution of the brain and higher cognition.

A new study in Cell investigating the gene SRGAP2 (SLIT-ROBO Rho GTPase activating protein 2) resequenced ∼0.4% of the euchromatin of chromosome 1 in haploid hydatidiform moles and discovered 3 novel genes–duplicates of SRGAP2 that are not found in Chimpanzee or Gorilla. Often times these recent duplicates are not important pseudogenes, as can be shown by high diversity in copy number with no selection for or against them, but one of the 3 new genes SRGAP2C is extremely fixed at two copies (one/chromosome), indicating that it is evolutionarily important. Indeed, concurrent studies show that SRGAP2C influences the development of synaptic spines, and increases the density of connections in the human brain and increase the speed of neural migration.

Evan Eichler, the first study’s author noted, “Ten years after the human genome was sequenced and declared done, we’re still finding new genes in new places that are really important to human brain function and evolution.” These findings also highlight a weakness in current sequencing techniques and the possibility of their application to disease gene discovery and diagnoses–especially if the genes were are miss in sequencing are some of the most important in what make us human.