Hox genes are the family of transcription factors that play a key role in the patterning of the anterior-posterior axis of all bilaterian animals. These genes display clustered organization and colinear expression. Expression boundaries of individual Hox genes usually correspond with morphological boundaries of the body. Previously, we studied Hox gene expression during larval development of the polychaete Alitta virens (formerly Nereis virens) and discovered that Hox genes are expressed in nereid larva according to the spatial colinearity principle. Adult Alitta virens consist of multiple morphologically similar segments, which are formed sequentially in the growth zone. Since the worm grows for most of its life, postlarval segments constantly change their position along the anterior-posterior axis.

Fibrosis is a major medical challenge, as it leads to irreversible tissue remodeling and organ dysfunction. Its progression contributes significantly to morbidity and mortality worldwide, with limited therapeutic options available. Extensive research on the molecular mechanisms of fibrosis has revealed numerous factors and signaling pathways involved. However, the interactions between these pathways remain unclear. A comprehensive understanding of the entire signaling network that drives fibrosis is still missing. The TGF-β and Notch signaling pathways play a key role in fibrogenesis, and this review focuses on their functional interplay and molecular mechanisms. Studies have shown synergy between TGF-β and Notch cascades in fibrosis, but antagonistic interactions can also occur, especially in cardiac fibrosis. The molecular mechanisms of these interactions vary depending on the cell context. Understanding these complex and context-dependent interactions is crucial for developing effective strategies for treating fibrosis.

Hox genes are the key determinants of different morphogenetic events in all bilaterian animals. These genes are probably responsible for the maintenance of regenerative capacities by providing positional information in the regenerating animal body. Polychaetes are well known for their ability to regenerate the posterior as well as the anterior part of the body. We have recently described the expression of 10 out of 11 Hox genes during postlarval growth of Alitta (Nereis) virens. Hox genes form gradient overlapping expression patterns, which probably do not contribute to the morphological diversity of segments along the anterior-posterior axis of the homonomously segmented worm. We suggest that this gradient expression of Hox genes establishes positional information along the body that can be used to maintain coordinated growth and regeneration.

Mesothelial cells line serosal cavities and internal organs, playing a vital role in maintaining serosal integrity and homeostasis. Their remarkable plasticity and ability to undergo mesothelial-to-mesenchymal transition (MMT) position them as key regulators of tissue repair. However, when normal repair processes fail, mesothelial cells can acquire a profibrotic phenotype. They actively contribute to all stages of fibrosis development, including inflammation, fibrin accumulation, myofibroblast differentiation, and extracellular matrix (ECM) remodeling. Fibrotic progression involves multiple cell types, and communication among them is essential for its perpetuation. Mesothelial cells are implicated in bidirectional crosstalk with fibroblasts, macrophages, lymphocytes, and endothelial cells of the serosal microenvironment through direct contact, paracrine signaling, and extracellular vesicle exchange. These interactions regulate immune cell recruitment, cytokine balance, endothelial permeability, and ECM deposition, while, in turn, immune and endothelial cells modulate mesothelial activation, proliferation, and transition. Understanding this complex network of intercellular communication provides new insights into fibrosis pathogenesis and reveals promising targets for antifibrotic therapies.

Retinoic acid (RA) plays an important role in vertebrate development and regeneration. RA signalling directly regulates the expression of Hox genes, being in this way involved in the patterning of the anterior-posterior (AP) axis of vertebrate embryos. So far the relationship between retinoic acid signalling and Hox genes has been shown only for chordates. In this study we incubated juvenile worms and regenerating worms of two polychaete species from the family Nereididae, Alitta virens and Platynereis dumerilii, with all-trans-retinal, the precursor of retinoic acid. Under the influence of all-trans-retinal the anterior expression boundary of Post2 Нох gene shifted towards the anterior end both in intact and in regenerating worms of both species. Our data indicate the existence of a relationship between RA signalling and Нох genes in Protostomia.