Tissue interactions govern pattern formation in the posterior lateral line of medaka

Abstract

1 Vertebrate organs are arranged in a stereotypic, species-specific position along the animal body 2 plan. Substantial morphological variation exists between related species, especially so in the vastly 3 diversified teleost clade. It is still unclear how tissues, organs and systems can accommodate such 4 diverse scaffolds. Here, we use the sequential formation of neuromasts in the posterior lateral line 5 (pLL) system of medaka fish to address tissue-interactions defining a pattern. We show that the 6 pLL pattern is established independently of its neuronal wiring, and demonstrate that the neuromast 7 precursors that constitute the pLL behave as autonomous units during pattern construction. We 8 uncover the necessity of epithelial integrity for correct pLL patterning by disrupting keratin 15 (krt15) 9 and creating epithelial lesions that lead to novel neuromast positioning. By using krt15/wt chimeras, 10 we determined that the new pLL pattern depends exclusively on the mutant epithelium, which 11 instructs wt neuromast to locate ectopically. Inducing epithelial lesions by 2-photon laser ablation 12 during pLL morphogenesis phenocopies krt15 genetic mutants and reveals that epithelial integrity 13 defines the final position of the embryonic pLL neuromasts. Our results show that a fine-balance 14 between primordium intrinsic properties and instructive interactions with the surrounding tissues is 15 necessary to achieve proper organ morphogenesis and patterning. We speculate that this logic 16 likely facilitates the accommodation of sensory modules to changing and diverse body plans.

Diversity of lateral line patterns and neuromast numbers in the genus Oryzias

“…Taken together, these data suggest that there are mechanisms that act specifically post-embryonically to shape pLL patterns and organ numbers, as has been previously suggested for other species (Nuñez et al, 2009;Pichon and Ghysen, 2004). But they also reveal that the origin of differences in patterning in certain cases can be traced back to differences during embryonic development (Seleit et al, 2017a(Seleit et al, , 2022. The genetic basis of those differences remains to be elucidated, but our results uncover a diversity of pLL patterns that is encoded at the level of developmental processes in Oryzias species and strains.…”

“…Intrigued by the differences observed in the adult pLL patterns among Oryzias species and strains, we decided to look at pLL patterns at the end of embryogenesis, using a number of representative species to gain a better understanding of the origin of those differences. We had previously reported that different embryonic pLL patterns exist in different teleost species (Seleit et al, 2017a(Seleit et al, , 2022, but whether they also differ within the Oryzias clade had not been addressed before. We analysed the final embryonic pLL pattern by looking at recently hatched larvae (N=10 for each species), within 24 h of exiting the chorion, and we noticed two different scenarios.…”

Organ-Founder Stem Cells Mediate Post-Embryonic Neuromast Formation In Medaka

“…To mimic the lack of cxcr4b in mature organs and in a cell-type specific manner, we used the K15 promoter to drive expression of the Cxcr7 receptor, a non-signaling (sinking) receptor that competes with Cxcr4b for the Cxcl12 ligand (Aman & Piotrowski, 2008;Dona et al, 2013;Naumann et al, 2010). Although specific for neural stem cells in the mature neuromast, the K15 promoter drives expression at earlier stages, after primary neuromasts were deposited by the primordium (Seleit et al, 2022). As expected for the over-expression of a functional Cxcr7, Tg(K15::Cxcr7) juveniles often lack secondary embryonic neuromasts, which depend on a proper chemokine signaling (Seleit et al, 2017) (Fig.…”

“…Animal experiments were conducted according to European Union animal welfare guidelines. The published transgenic lines used in this study are : Tg(Eya1:mCFP), Tg(Eya1:EGFP) (Seleit et al, 2017), Tg(K15:H2B-RFP), Tg(K15:H2B-EGFP) (Seleit, Krämer et al, 2017), Tg(K15:LifeAct-tagRFP) (Seleit et al, 2022). Tg(Kremen1:mYFP) was generously provided by J. Wittbrodt's lab.…”

“…Design of gRNAs was done using CCTop (Stemmer et al, 2015). Cloning of gRNAs was done as described before (Seleit et al, 2022;Seleit, Krämer et al, 2017;Stemmer et al, 2015) and used at a concentration of 15 ng/µl together with 150 ng/µl Cas9 mRNA. We injected 1-cell stage medaka embryos from Tg(Eya1:EGFP) or Tg(K15:lifeAct-tRFP), screened the resulting larvae for lateral line phenotypes and grew them to adulthood.…”