Ivashkin, E. G. | bioRxiv Science

bioRxiv2023

Spontaneous Intersibling Polymorphism in the Development of Dopaminergic Neuroendocrine Cells in Sea Urchin Larvae: Impacts on the Expansion of Marine Benthic Species

Plasticity of the nervous system enables the formation of the most adaptive neural circuits and the corresponding behavior of animals. The mechanism by which plasticity arises during development and its involvement in animal adaptation is one of the astonishing questions. Sea urchin larvae are known for their evolutionary and ecological diversity as well as their developmental forms and behavioral patterns. This research addresses the intricate neuroendocrine adaptations that govern larval development of sea urchins, focusing on the coordination between dopaminergic (DA) and serotonergic (5-HT) neurons. The study reveals a heterochronic polymorphism in the appearance of post oral DA neurons and confirms the stable differentiation pattern of apical 5-HT neurons in the larvae of Mesocentrotus nudus and Paracentrotus lividus. We demonstrate that an increased number of DA cells and DA application correlate with downward swimming of the larvae. In contrast, 5-HT cells and serotonin application unsure larval upward swimming. As a result, the 5-HT/DA ratio underlay stage-dependent vertical distribution of the larvae within the water column. In larvae of the same age, the precise balance of 5-HT and DA cells underlie the basis for the different potentials of individuals for upward and downward swimming. This coordination in humoral regulation underlies shifts in larval behavior within a single generation. Based on our findings on DA-cells polymorphism, we have proposed a model illustrating how the balance between the serotonin and dopamine systems, shaped by heterochrony in DA cell appearance, impacts larval behavior, reduces competition between siblings and ensures optimal population expansion. The study explores the evolutionary and ecological implications of these neuroendocrine adaptations in marine species.

developmental biology↗

bioRxiv2023

Expanded Expression of Pro-Neurogenic Factor SoxB1 during Larval Development of gastropod Lymnaea stagnalis Suggests Preadaptation to Prolonged Neurogenesis in Mollusca

The diversity in the organization of the nervous system in mollusks raises intriguing questions about its development and evolution. Our study aims to gain a deeper understanding of how the nervous system forms in Mollusca by examining the involvement of SoxB-family transcription factors in the early development of neurogenic zones. Specifically, we explore the expression patterns of two SoxB genes in the gastropod Lymnaea stagnalis, namely Ls-SoxB1 and Ls-SoxB2, across various developmental stages. Through a combination of in situ hybridization chain reaction, immunohistochemistry, and proliferation assays, we examine the dynamic spatial distribution of Ls- SoxB1 and Ls-SoxB2, with a particular emphasis on the formation of central ring ganglia and the identification of active proliferative zones. Our findings reveal that Ls-SoxB1 exhibits expanded ectodermal expression from the gastrula to the postmetamorphic stage, evident at both transcriptional and translational levels. Throughout larval development, Ls-SoxB1 is expressed in the ectoderm of the head, foot, and visceral complex, as well as in ganglia anlagen and sensory cells. In contrast, the expression of Ls-SoxB2 in the ectoderm is observed until the veliger stage, after which it persists in subepithelial layer cells and ganglia rudiments. Proliferation assay reveals a uniform distribution of dividing cells in the ectoderm at all developmental stages, indicating the absence of distinct neurogenic zones with increased proliferation in gastropods. Our findings highlight that Ls-SoxB1 exhibit widespread expression patterns in both location and time compared to other Lophotrochozoa species. This prolonged expression of SoxB genes in gastropods can be interpreted as a form of transcriptional neoteny, playing a crucial role in the diversification of nervous systems. Thus, it serves as a preadaptation to prolonged neurogenesis and an increase in the central nervous system complexity in Mollusca.

developmental biology↗