Transcriptomics Unravels Molecular Players Shaping Dorsal Lip Hypertrophy in the Vacuum Cleaner Cichlid, Gnathochromis Permaxillaris

Abstract

Background:Teleosts display a spectacular diversity of craniofacial adaptations that often mediate ecological specializations. A considerable amount of research has revealed molecular players underlying skeletal craniofacial morphologies, but less is known about soft craniofacial phenotypes. Here we focus on a bizarre example of lip hypertrophy in the Lake Tangnayika cichlid, Gnathochromis permaxillaris, that is considered to be a dietary adaptation to suck invertebrates out of narrow crevices. In this study, we investigate the molecular and regulatory basis of lip development G. permaxillaris, using a comparative transcriptomic approach.Results: We identified a gene regulatory network involved in tissue overgrowth and cellular hypertrophy, potentially associated with the formation of a locally restricted hypertrophic lip in a teleost fish species. Of particular interest were the increased expression level of apoda and fhl2, as well as reduced expression of cyp1a, gimap8, lama5 and rasal3, in the hypertrophic lip region which have been implicated in formation of lip structure in other vertebrates. Among the predicted upstream transcription factors, we found reduced expression foxp1 in the hypertrophic lip region, which is known to act as repressor of cell growth and proliferation and its function has been associated with hypertrophy of upper lip in human. Conclusion: Our results provide a genetic foundation for future studies of molecular players shaping soft and exaggerated, but locally restricted, craniofacial morphological changes in fish and perhaps across vertebrates.

Ecological speciation promoted by divergent regulation of functional genes within African cichlid fishes

“…Genes under divergent regulation from cis -sQTLs were enriched for a large number of GO terms, which were predominately related to immune system processes, as well as responses to bacteria and other biological stimuli (n = 97; FDR- corrected P < 0.05; Supplementary Table 10). Interestingly, we also found enrichment of terms involved in positive regulation of the ERK/MAPK (Extracellular signal-Regulated Kinase/Mitogen-Activated Protein Kinase) cascade, which is a known central regulator of tooth development in vertebrates 61–64 , as well as processes involved in regulation of cell adhesion and cell junction assembly which have been implicated in lip morphogenesis linked to foraging strategy in a Lake Tanganyika cichlid 65 .…”