Novosibirsk Scientists Find Unusual Genetic Features in a Free-Living Marine Worm

Novosibirsk scientists led by Dr. Nikolai Rubtsov, Head of the NSU Department of Cytology and Genetics and Head of the Laboratory of Morphology and Functions of Cellular Structures at the Institute of Cytology and Genetics SB RAS, offered a new model for studying the early stages of genome evolution after full genomic duplication.


The genomes (a set of genes contained in one set of organism chromosomes) of most existing animal species and plants arose as a result of one or several rounds of complete genomic duplication. Complete genome duplication is a large-scale gene mutation that leads to the formation of a genome with an additional copy of the entire genome of the original individual.

Constant development and improvement of the methodological base makes it possible to receive and accumulate huge data sets of genomic sequences from various organisms from the simplest and ending with a human being. This makes it possible to compare genomes at the level of genomic sequences. Comparison of genomic sequences not only detects traces of full-genomic duplication events from long ago (for example, in bone fish 350 million years ago), but also allows us to study the stages of double genome reorganization in the early stages of evolution. However, the mechanisms for stabilizing the genome after its doubling are still poorly understood. The reason for this is an almost complete absence of model organisms whose genome has undergone genomic duplication relatively recently.

A free-living marine worm, Macrostomum lignano, can become a new potential model for studying the early stages of the evolution of the genome after full genomic duplication. This worm has a number of features that make it attractive for exploring a variety of research interests from studying regeneration and aging processes to studying hermaphroditism.

Kira Zadesynets, Ph.D., Laboratory of Morphology and Functions of Cellular Structures at the Institute of Cytology and Genetics SB RAS talked about this work,

"Recently, some features of the karyotype of M. lignano made it a subject for conducting a cycle of cytogenetic studies in our Laboratory. Karyotype M. lignano contains 8 chromosomes, two of them are very large chromosomes, and the remaining six are small. We demonstrated that the karyotype in this species is unstable and this instability is primarily due to the presence of one or two additional copies of a large chromosome. It is known that aneuploidy in most organisms (yeast, plants, invertebrates, mammals) leads to sterility, serious malformations and even death. However, we have shown that the aneuploid forms in the macrostoma are not only viable, but also fertile".  

Kira Zadesynets continues:

"We assume that the ancestral form of the karyotype in the macrostoma contained only 6 chromosomes. After full genome duplication, the karyotype increased to 2n = 12, while in M. lignano it decreased to 2n = 8 as a result of chromosomal fusions. In our study, we presented the first evidence that the genome of this worm probably occurred during the evolution of the ancestral genome, undergoing a round of full genomic duplication. This was accompanied by the fusion of all chromosomes from one chromosome set, to form one large metacentric chromosome (see figure). In this way the species-specific karyotype of macrostoma 2n = 8 is a latent tetraploid karyotype, in an anploid form of the macrostoma along a large chromosome - hidden polyploid forms"