The mechanisms of occurrence of a huge variety of cell types and morphological forms in the process of development of higher organisms have always been of interest to biologists of different specialties. In early experiments of the last millennium on tissue transplantation from one embryo to another in multicellular organisms, it was shown that intercellular interactions play a leading role in the regulation of animal development. It has been suggested that the pathways of cell development are regulated by secreted signal molecules, and the interaction of embryonic bookmarks through determination and differentiation leads to a form-forming effect. In the last two decades, geneticists and biochemists have made significant progress in the study of information dissemination in ontogenesis (Gilbert, 1995; Korochkin, 1999; Jonhston and Gallant, 2002).
The role of signaling systems in the development of organisms and their properties
It is well established that in developing embryos of various representatives of vertebrates and invertebrates, intercellular interactions are coordinated by a set of signaling pathways. Most of the intercellular signals are transmitted by a small number of differently studied major signaling gene cascades associated with the activity of certain signal molecules (ligands, receptors, etc.) and designated (Mumm, Kopan, 2000; Tarchevsky, 2002; Serov, 2003; Pires-daSilva, 2003). These include Hh (Hedgehog) signaling pathways (Ingham and McMahon, 2001); Wnt (wingless) (Cadigan and Nusse, 1997); Notch (Mumm and Kopan, 2000); growth factors: TGF-? (Massague, Chen, 2000), EGFR (Freeman, 2002), RTK (Shemarova, 2003), JAK/STAT (Luo and Dearolf, 2001); nuclear hormone receptors (Glass and Rosenfeld, 2002). Prototypes of various multi-component signaling systems with a high degree of molecular signaling homology can be found in prokaryotes and lower eukaryotes. In the transition to multicellular eukaryotes, signal proteins undergo structural changes and form protein complexes; the efficiency of signal transduction increases (Shemarova, 2003; Shpakov et al., 2003).
Despite different final results of determination and differentiation in the ontogenesis of invertebrates and vertebrates, conservatism is observed in the development of the same signal cascade in different living organisms. In genomes of different types of genes that control development, they are evolutionarily conservative and have similar functions. For example, the Hh signaling system, in which the Hedgehog family proteins are secret ligands, has been detected in humans, mice, chickens, frogs, fish, sea urchins, leeches and insects (Ingham and McMahon, 2001). The Wnt pathway is also common among animals. Wnt proteins constitute one of the largest families of signal molecules in humans, mice, frogs, Caenorhabditis elegans, and drosophila (Cadigan and Nusse, 1997; Baonza and Freeman, 2002).
Along with strict conservatism, gene signaling systems have a high degree of flexibility in responding to intercellular signals. Each of them is repeatedly included in different tissues during the development of individuals, regulating the spatial and temporal separation of the expression of genes that determine different cell destinies. Thus, proteins of the Hh family are considered to be participants in cellular determination and differentiation, cell division, and mediators of many basic processes of embryonic growth and development. Invertebrates, only a small number of morphological parts of the body are not affected by the Hh-signal (Ingham and McMahon, 2001). In H-protein flies, the hh-proteins are expressed in the cells of the posterior region of each imaging disc. They play a central role in the embryonic development of the wing, eye, limbs, gonads, abdomen, intestines, and tracheas (Mohler, Vani, 1992; Zhang, Kalderon, 2000; Glazer, Shilo, 2001). At the same time, members of the Wnt family of proteins participate in different development processes. In drosophila, they are necessary for the organization of the central nervous system, determination of the region of the wing and eye primordial areas, limitation of the size of the eye area in the disk, initiation of the boundary between the eye and adjacent head structures, specialization of eye cells and head cuticles (Ng et al., 1996).
To be continued...