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Project titlePatterns of recovery and the role of the nervous system in the regeneration of Annelida

AffiliationFederal State Budgetary Educational Institution of Higher Education "Saint-Petersburg State University",

Keywordsneurogenesis, nervous system, innervation, neurotransmitters, growth factors, signaling, regulation, homeostasis, regeneration, experimental embryology, morphogenesis, patterning, invertebrates, Spiralia, Annelida

Annotation
The integrating role of the nervous system (NS) in physiological and behavioral responses has been well studied; however, in the context of a developing organism, its influence on morphogenesis and differentiation is no less important, but still poorly understood, especially in invertebrates. The interdependence of the formation of the nervous system and effector organs provides a key to understanding the most complex improvements of the whole body, organs and tissues in the course of evolutionary changes. Annelids are the most interesting organismic model with phenomenal abilities of the nervous system to control positional information, tissue homeostasis, reproduction and regeneration. Experiments on denervation, transplantation, transection and abduction of the ventral nerve cord (VNC) justified the opinion about the necessity and sufficiency of the damaged end of the VNC for the induction of the development of a regenerative bud. At present, annelids nervous system are given not only trophic and organizing functions, but also of great importance in creating an axial pattern that controls the specificity of morphogenesis. Despite the vivid experimental evidence of the necessity of NS for the regeneration of annelids, the specific mechanisms of its influence remain a mystery. First of all, by analogy with vertebrates, nerves can be a local source of signaling molecules, the identification of which is the most urgent task. The second possible way of regulation on the part of the NS is an auxiliary role for other cellular types of the regenerative response. The migratory elements temporarily associated with NS are phagocytes, neoblasts, and germline cells. What are the subtle interactions between NS and regenerate precursors remains to be seen. Thirdly, for annelids a vivid and unique in many respects role of the systemic regulation of regeneration and puberty through neuroendocrine secretion has been described. In many annelids, after removal of the brain (the source of the hormone), gamete maturation is activated, and the regeneration of the segments becomes impossible. To decipher the described phenomena, we have proposed this project. Taking into account the modern level of scientific technologies, the implementation of the project will undoubtedly open up new facets of regenerative biology. Within the framework of the project, it is planned to consider a model of normal post-traumatic regeneration and experimental heteromorphosis after the elimination of nerve elements in Annelida representatives. The solution to the problem ranges from molecular and subcellular scales to organismal ones. As a starting point, a comparative descriptive analysis of the dynamics of nerve recovery, their mediator tropism and transcriptome profile will be carried out. On the experimental material (after denervation and decapitation), the corresponding deviations of the recovery process will be traced.

Expected results
As a result of the project, new fundamental scientific data will be obtained on the outstanding role of the nervous system in the regeneration of annelids. We plan to describe in detail the morpho-functional regularities of the restoration of nerve elements, as well as their participation in the control of the surrounding tissues. Such results are of fundamental importance for understanding the functioning and stability of living systems, since they open up new facets of regulatory mechanisms. How variable and with what the specific mechanisms of regeneration are correlated will be clarified for the models we have chosen, which will significantly increase the resolution of the comparative analysis of the phenomena of maintaining integrity. The evolution of regenerative abilities and its explanation is one of the most pressing problems of world science. The expected results of the project are comprehensive and functional, which meets international standards. Since we plan to identify both the systemic and molecular factors of the regenerative response, the prerequisites will be created for translating the knowledge gained at a wide range of objects into the practice of medical development. The involvement of our experimental developments in the educational process will be carried out in the implementation of practical and theoretical university courses. The results of the project will be included in the diploma theses of the performers.

Annotation of the results obtained in 2022
At the 2022/2023 stage, a detailed characterization of the recovery of the nervous system of A. virens was given both at the level of processes and in the volume of the cell mass. The stages of growth and differentiation of serotonergic elements of the nervous system were traced. Using TEM and studying the dynamics of cell proliferation in A. virens, the recovery of BNC cell mass was described. The neural elements of the regenerate develop from two sources - from the preexisting nerve elements of the segment adjacent to the wound, as well as from the ventral epithelium of the regenerating kidney. The influence of the nervous system on the regeneration of segments was studied in experiments on the removal of the ventral nerve cord from the site of amputation and after removal of the head ganglion as part of the prostomium. These effects influenced the growth and development of the regenerate. In both cases, we noted compensatory innervation from the peripheral nervous system, but it is not sufficient for a complete and normal restoration of the lost part of the animal's body. Apparently, in addition to the presence of innervation of the regenerate, the correct organization of the vascular bundles of the BNC neuropil growing on the ventral side of the body is of key importance. Based on the results of transcriptome assembly and analysis, and with the help of inhibitory analysis, candidate genes specific for the damaged nervous system involved in the early regeneration processes of A. virens were identified.

Publications

1. Kairov A., Kozin V. ЭКСПРЕССИЯ ГОМОЛОГА ENGRAILED У ЛИЧИНОК И ЮВЕНИЛЕЙ АННЕЛИДЫ ALITTA VIRENS РАСКРЫВАЕТ ОСОБЕННОСТИ ФОРМИРОВАНИЯ СЕГМЕНТОВ ИЗ ЗОНЫ РОСТА Онтогенез, - (year - 2023)

2. Shalaeva A.Y., Kozin V.V. Cell proliferation indices in regenerating Alitta virens (Annelida, Errantia) Cells, Cells 2023, V. 12, P. 1354. (year - 2023) https://doi.org/10.3390/cells12101354

3. Kozin V.V. Аннелиды как объекты EvoDevo Юбилейная научная конференция «Николай Константинович Кольцов и биология XXI века», с. 52-53 (year - 2022)

4. Kozin V.V., Borisenko I.E. Участие нервной системы в регуляции ранних этапов регенерации у полихеты Alitta virens Юбилейная научная конференция «Николай Константинович Кольцов и биология XXI века», с. 52 (year - 2022)

5. Shalaeva A., Belyaeva M., Tarasov M., Kozin V. Экспериментальные исследования роли нервной системы при регенерации Alitta virens Беломорская студенческая научная сессия СПбГУ — 2023, С. 101 (year - 2023)

6. Shalaeva A.Y., Kozin V.V. Регенеративный ответ нервной системы после ампутации задних сегментов у ювенильных Alitta virens Цитология, том 64, № 7, с. 762. (year - 2022) https://doi.org/10.31857/S004137712207001X

7. Shalaeva A.Y., Kozin V.V. Качественный и количественный анализ пролиферации в ходе регенерации у Alitta virens (Annelida, Errantia) Юбилейная научная конференция «Николай Константинович Кольцов и биология XXI века», с. 90-91 (year - 2022)

Annotation of the results obtained in 2021
The nervous system is a well–known regulator of regeneration in many animals (vertebrates and invertebrates), which plays a key role in initiating the entire complex of processes. During the development of methodological approaches, an approximate protocol of experimental effects on denervation and decapitation was developed. The most successful experiments were conducted on decapitation of objects aimed at removing the head part of the nervous system in order to assess its effect on the course of posterior regeneration. We found that during decapitation, the recovery of the lost segments slows down greatly, and the regenerative kidney itself changes greatly in size, although morphological signs such as parapodia with chetes, pygidium and cirrus are still present in the objects. With the longest time interval between operations (7 days) we observed the strongest morphological changes, in which only severely deformed pygidium and cirri were formed, and signs of segmentation were not detected at all. Significant deviations were also noted at the tissue level: the nervous system in regenerates turns out to be differently differentiated than in control samples, and some of its elements are completely absent. The data obtained allow us to assume an important role of the anterior part of the nervous system in the regeneration of annelids. The regulation of reparative processes on the part of the nervous system can be associated not only with their initiation, but also with further stages of the entire process, including controlling the segmentation of the regenerative kidney, differentiation of its segmented parts and the speed of the process as a whole.

Publications

1. Kairov A., Kostyuchenko R., Kozin V. Определение вовлеченности Wnt-сигналинга в процессы формирования ларвальных и постларвальных сегментов у Alitta virens Беломорская студенческая научная сессия СПбГУ – 2022. Тезисы докладов., С. 54 (year - 2022)

2. Shalaeva A., Denisova S., Kozin V. Towards deciphering signaling interactions, cellular populations, and ultrastructural changes at the early stages of Alitta virens regeneration Беломорская студенческая научная сессия СПбГУ – 2022. Тезисы докладов., C. 53 (year - 2022)

3. Shalaeva A., Kozin V. Experimental model to test the influence of cerebral ganglion on the posterior regeneration of the annelid Alitta virens Developmental Biology New York (3rd Annual Free Undergraduate-Focused Developmental Biology Conference), P. 13 (year - 2021)