Turritopsis dohrnii (Cnidaria, Hydrozoa, Hydroidolina, Anthoathecata) is the only known metazoan that is capable of reversing its life cycle via morph rejuvenation from the adult medusa stage to the juvenile polyp stage. Here, we present a complete mitochondrial (mt) genome sequence of T. dohrnii, which harbors genes for 13 proteins, two transfer RNAs, and two ribosomal RNAs. The T. dohrnii mt genome is characterized by typical features of species in the Hydroidolina subclass, such as a high A+T content (71.5%), reversed transcriptional orientation for the large rRNA subunit gene, and paucity of CGN codons. An incomplete complementary duplicate of the cox1 gene was found at the 5' end of the T. dohrnii mt chromosome, as were variable repeat regions flanking the chromosome. We identified species-specific variations (nad5, nad6, cob, and cox1 genes) and putative selective constraints (atp8, nad1, nad2, and nad5 genes) in the mt genes of T. dohrnii, and predicted alterations in tertiary structures of respiratory chain proteins (NADH4, NADH5, and COX1 proteins) of T. dohrnii. Based on comparative analyses of available hydrozoan mt genomes, we also determined the taxonomic relationships of T. dohrnii, recovering Filifera IV as a paraphyletic taxon, and assessed intraspecific diversity of various Hydrozoa species.
The prospects for application of metagenomic technologies in environmental studies are discussed. The advantages in investigating the taxonomic composition of aquatic and terrestrial ecosystems, as well as examples of trophic and phoric relationships found in ecosystems using the metagenomic approach, are described. The capabilities of metagenomics to study prokaryotic communities in complicated environments such as soils or animal intestines are shown. The role of relic DNA in the metagenome and the possibilities to study ancient organisms are highlighted. Particular attention is paid to the criticism of metagenomic technologies related to the low reproducibility of the sequencing data. Common methodological mistakes in bioinformatics processing of metagenomic data leading to misleading results are considered.
Bipedalism, speech, and intellect are the most prominent traits that emerged in the evolution of Homo sapiens. Here, we describe a novel genetic cause of an “involution” phenotype in four patients, who are characterized by quadrupedal locomotion, intellectual impairment, the absence of speech, small stature, and hirsutism, observed in a consanguineous Brazilian family. Using whole-genome sequencing analysis and homozygous genetic mapping, we identified genes bearing homozygous genetic variants and found a homozygous 36.2 kb deletion in the gene of glutamate receptor delta 2 (GRID2) in the patients, resulting in the lack of a coding region from the fifth to the seventh exons. The GRID2 gene is highly expressed in the cerebellum cortex from prenatal development to adulthood, specifically in Purkinje neurons. Deletion in this gene leads to the loss of the alpha chain in the extracellular amino-terminal protein domain (ATD), essential in protein folding and transport from the endoplasmic reticulum (ER) to the cell surface. Then, we studied the evolutionary trajectories of the GRID2 gene. There was no sign of strong selection of the highly conservative GRID2 gene in ancient hominids (Neanderthals and Denisovans) or modern humans; however, according to in silico tests using the Mfold tool, the GRID2 gene possibly gained human-specific mutations that increased the stability of GRID2 mRNA.
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