Earthworm coelomocytes (e.g. amoebocytes and eleocytes) participate in diverse physiological processes from nutrition storage to immune defense. While the morphology and functional attributes of adult coelomocytes have been extensively studied, their origin and ontogeny are largely unexplored during earthworm development. To uncover this knowledge gap, we examined the emergence, distribution, and molecular characteristics of amoebocytes vs . eleocytes during embryogenesis (E1-E4 stages) of Eisenia andrei earthworms. Applying light-microscopy and flow cytometry, we observed a sequential manifestation of coelomocyte subsets: amoebocytes predominated in E3 stage, whereas eleocytes became more abundant in E4; although amoebocytes remain prevalent overall. In parallel, the expression dynamics of key earthworm immune-related genes evidenced characteristic differences. The transcripts of evolutionarily conserved TLR and MyD88 displayed constitutive expression throughout all embryonic stages (E1-E4). Conversely, LBP/BPI gene expression decreased, while CCF mRNA level increased during Eisenia embryogenesis. Moreover, antimicrobial effectors ( lysenin and lysozyme ) were progressively increased from E1 to E4 stages. Our novel experimental data shed more light at molecular and cellular levels into the development and maturation of immune cell populations during earthworm embryogenesis. • Embryonic coelomocytes appeared sequentially in E. andrei earthworms. • Amoebocytes are predominant in E3 and E4 stages, but eleocytes are more abundant in E4. • TLR and MyD88 transcripts displayed constitutive expression in all stages. • LBP/BPI mRNA level decreased, while CCF transcript increased during embryogenesis. • Lysenin and lysozyme mRNA levels are enhanced from E1 to E4 stages.
Bodó et al. (Sun,) studied this question.