Russian Journal of Developmental Biology

Placozoa (Trichoplax) — highly simplified free-living metazoans originating during the peak of marine biodiversity diversification. Placozoans are morphologically and functionally asymmetric organisms lacking muscles, a nervous system, and clear body symmetry. Despite their structural simplicity, they exhibit complex behaviors, including social interactions. Research on Placozoa and the establishment of this phylum has a long history, whichwe present here as a chronological timeline spanning from early studies of their biology and morphology to modern genomic and transcriptomic analyses. This review synthesizes recent advances in Placozoan biology and critically evaluates accumulated data. Based on this analysis, weidentify the most promising future research directions for this enigmatic group.

Transcriptional activity in cells has traditionally been viewed solely in the context of protein biogenesis, serving as a step in the expression of genetic information. However, the discovery of diverse non-coding and regulatory RNAs — many of which function in the nucleus — calls for a reevaluation of transcription’sbroader role in cellular processes. In gametogenesis, transcription has primarily been studied in relation to mRNA stockpiling, particularly in species exhibiting hypertranscriptional oogenesis, where lampbrush chromosomes persist in the oocyte nucleus over an extended period. This review reassesses the significance of transcription in meiosis, integrating data on its dynamic regulation during oogenesis and spermatogenesis across different organisms. Special focus is given to evolutionary conserved mechanisms underlying meiotic recombination of chromosomes. Using heteromorphic and unpaired sex chromosomes as a model, weexplore the peculiarities of inheritance of epigenetic information in the absence of meiotic pairing influence. Additionally, wehighlight features of the of the RNA polymerase II complex, which create the necessary conditions for proper alignment and synapsing of homologous chromosomes during meiotic recombination. These insights advance our understanding of transcription as a critical player in ensuring accurate chromosomal segregation and correct reparation of double breaks during meiotic recombination.

Endoplasmic reticulum (ER) stress and the resulting unfolded protein response (UPR) play an important role in functioning and progression of many types of tumors. In particular, ER stress can both stimulate and suppress cell motility, invasiveness, and metastasis. Contribution of ER stress induced by varying mechanisms to changes of cell motility parameters of normal and tumor cells is poorly understood. In this study, weinvestigated the different effects of ER stress inducers bortezomib, tunicamycin, and dithiothreitol (DTT) on cell motility, area, and shape of normal and tumor cells of epidermal origin, HaCaT and A431, respectively, in the presence of the agent and after its removal from the culture medium. We showed that HaCaT cell motility was suppressed by bortezomib, tunicamycin, and DTT and was restored after removal of the agent. Effects of bortezomib and DTT are accompanied by a reversible decrease in area and an increase in the form factor: HaCaT cells become rounded, with fewer protrusions. The effect of bortezomib on A431 cells leads to an irreversible decrease in motility without significant changes in area or shape; the decrease in motility after incubation of cells with tunicamycin and DTT, on the contrary, is reversible. In conclusion, ER stress inducers suppress cell motility of immortalized HaCaT keratinocytes and A431 epidermoid carcinoma cells regardless of the induction mechanism. Observed changes in cell area and shape, as well as the reversibility of these phenomena, depend on the cell type and the induction mechanism.