SDF-1/CXCR4 signal is involved in the induction of Primordial Germ Cell migration in a model marine fish, Japanese anchovy (Engraulis japonicus)

Primordial germ cells (PGCs) are pivotal for gonadal development and reproductive success. Though artificial induction of sterility by targeting PGCs are gaining popularity due to its advantages in fish surrogacy and biodiversity management, it is often skill and time intensive. In this study, we have focused on understanding the role of PGCs and the chemotactic SDF-1/CXCR4 signaling on gonad development of Japanese anchovy (JA, Engraulis japonicus), an upcoming marine model organism with eco-commercial values, with an aim to develop a novel, easy, and versatile gonad sterilization method. Our data showed that PGC migration related genes, i.e., sdf-1a, sdf-1b, cxcr4a, cxcr4b and vasa, are phylogenetically closer relatives of respective herring (Clupea harengus) and zebrafish (Danio rerio) homolog. Subsequently, PGC marking and live tracing experiments confirmed that PGC migration in JA initiates from 16 hours post fertilization (hpf) followed by PGC settlement in the gonadal ridge at 44 hpf. We found that overexpression of zebrafish sdf-1a mRNA in the germ cell suppresses cxcr4a and increases cxcr4b transcription at 8 hpf, dose dependently disrupts PGC migration at 24-48 hpf, induces PGC death and upregulates sdf-1b at 5 days post hatching. 48 h of immersion treatment with CXCR4 antagonist (AMD3100, Abcam) also accelerated PGC mismigration and pushed the PGC away from gonadal ridge in a dose responsive manner, and further when grown to adulthood caused germ cell less gonad formation in some individuals. Cumulatively, our data, for the first time, suggests that JA PGC migration is largely regulated by SDF1/CXCR4 signaling, and modulation of this signaling has strong potential for sterile, germ cell less gonad preparation at a mass scale. However, further in-depth analysis is pertinent to apply this methodology in marine fish species to successfully catapult Japanese anchovy into a true marine fish model.

Modeling the SDF-1/CXCR4 protein using advanced artificial intelligence and antagonist screening for Japanese anchovy

SDF-1/CXCR4 chemokine signaling are indispensable for cell migration, especially the Primordial Germ Cell (PGC) migration towards the gonadal ridge during early development. We earlier found that this signaling is largely conserved in the Japanese anchovy (Engraulis japonicus, EJ), and a mere treatment of CXCR4 antagonist, AMD3100, leads to germ cell depletion and thereafter gonad sterilization. However, the effect of AMD3100 was limited. So, in this research, we scouted for CXCR4 antagonist with higher potency by employing advanced artificial intelligence deep learning-based computer simulations. Three potential candidates, AMD3465, WZ811, and LY2510924, were selected and in vivo validation was conducted using Japanese anchovy embryos. We found that seven transmembrane motif of EJ CXCR4a and EJ CXCR4b were extremely similar with human homolog while the CXCR4 chemokine receptor N terminal (PF12109, essential for SDF-1 binding) was missing in EJ CXCR4b. 3D protein analysis and cavity search predicted the cavity in EJ CXCR4a to be five times larger (6,307 Å³) than that in EJ CXCR4b (1,241 Å³). Docking analysis demonstrated lower binding energy of AMD3100 and AMD3465 to EJ CXCR4a (Vina score -9.6) and EJ CXCR4b (Vina score -8.8), respectively. Furthermore, we observed significant PGC mismigration in microinjected AMD3465 treated groups at 10, 100 and 1 × 105 nM concentration in 48 h post fertilized embryos. The other three antagonists showed various degrees of PGC dispersion, but no significant effect compared to their solvent control at tested concentrations was observed. Cumulatively, our results suggests that AMD3645 might be a better candidate for abnormal PGC migration in Japanese anchovy and warrants further investigation.