The presence and expression of the HIF-1α in the respiratory intestine of the bronze Corydoras Corydoras aeneus (Callichthyidae Teleostei)

Quest for breathing: proliferation of alveolar type 1 cells

There is much evidence that the vertebrate lung originated from a progenitor structure which was present in bony fish. However, critical basic elements for the evolution of breathing in tetrapods, such as the central rhythm generator sensitive to CO₂/pH and the pulmonary surfactant, were present in the lungless primitive vertebrate. This suggests that the evolution of air breathing in all vertebrates may have evolved through exaptations. It appears that the capability for proliferation of alveolar type 1 (AT1) cells is the "critical factor" which rendered possible the most radical subsequent innovation-the possibility of air breathing. "Epithelial remodeling," which consists in proliferation of alveolar cells-the structural basis for gas diffusion-observed in the alimentary tract of the gut-breathing fishes (GBF) has great potential for application in biomedical research. Such a process probably led to the gradual evolutionary development of lungs in terrestrial vertebrates. Research on the cellular and molecular mechanisms controlling proliferation of squamous epithelial cells in the GBF should contribute to explaining the regeneration-associated phenomena that occur in mammal lungs, and especially to the understanding of signal pathways which govern the process.

Elevating EGFR-MAPK program by a nonconventional Cdc42 enhances intestinal epithelial survival and regeneration

The regulatory mechanisms enabling the intestinal epithelium to maintain a high degree of regenerative capacity during mucosal injury remain unclear. Ex vivo survival and clonogenicity of intestinal stem cells (ISCs) strictly required growth response mediated by cell division control 42 (Cdc42) and Cdc42-deficient enteroids to undergo rapid apoptosis. Mechanistically, Cdc42 engaging with EGFR was required for EGF-stimulated, receptor-mediated endocytosis and sufficient to promote MAPK signaling. Proteomics and kinase analysis revealed that a physiologically, but nonconventionally, spliced Cdc42 variant 2 (V2) exhibited stronger MAPK-activating capability. Human CDC42-V2 is transcriptionally elevated in some colon tumor tissues. Accordingly, mice engineered to overexpress Cdc42-V2 in intestinal epithelium showed elevated MAPK signaling, enhanced regeneration, and reduced mucosal damage in response to irradiation. Overproducing Cdc42-V2 specifically in mouse ISCs enhanced intestinal regeneration following injury. Thus, the intrinsic Cdc42-MAPK program is required for intestinal epithelial regeneration, and elevating this signaling cascade is capable of initiating protection from genotoxic injury.

Chemoreceptors as a key to understanding carcinogenesis process

The tissue organization field theory (TOFT) presented completely new, different from the previous one, perspective of research on neoplasm processes. It implicates that secretory neuroepithelial-like cells (NECs), putative chemoreceptors are probably responsible for the control of squamous epithelial cells proliferation in the digestive tract during hypoxia in gut breathing fish (GBF). On the other hand, chemoreceptors dysfunction can lead to uncontrolled proliferation and risk of cancer development in mammals, including humans. The studies on NECs like cells (signal capturing and transduction) may be crucial for understanding the processes of controlling the proliferation of squamous epithelial cells in the digestive tract of GBF fish during hypoxia states. This knowledge can contribute to the explanation of cancer processes.

From epithelial remodelling to carcinogenesis

The novel cancer theory named 'the tissue organization field theory' (TOFT) suggests that carcinogenesis is a process analogous to embryonic development, whereby organs are formed through interactions among different cell types. The suggested 'morphological remodelling' of the epithelium under hypoxia in gut breathing fish (GBF) has many common features with carcinogenesis. It appears that research into the relationship among epidermal growth factor receptor (EGFR), hypoxia inducible factor (HIF) as well as hypoxia and normoxia states in GBF fishes can be crucial in learning about the steering mechanisms of squamous epithelium proliferation, leading to a better understanding of carcinogenesis.