Abstract
Background: ETB-/- mutation is a major cause of HSCR, a neurocristopathy known for its enteric nervous system failure. Other than regulating ENCC migration, ETB mediates ET-1 clearance. Consequently, ETB may indirectly affect ET-1/ETA signaling, which controls CNCC migration and craniofacial development. Interestingly, it was hypothesized that “domestication syndrome” arise from changes in neural crest determining genes, including ETA and ETB. While ETA-/- animals are known to suffer severe dysmorphology resembling CATCH22 syndrome, we hypothesize that sl/sl rat, an ETB-/- HSCR model animal, may exhibit subtle craniofacial changes through indirect control. These features may share resemblance to those of domestication syndrome. Methods: Ten rat pups with an average age of 88 hours were anaesthetized with 5% isoflurane and culled via exsanguination. Tail tips were removed for genotyping. Head tissue were stained in 1.5% iodine for two weeks prior to micro-CT scanning. In vivo micro-CT scanning of cranial specimen was performed followed by ex vivo micro-CT scanning of 2 samples for image quality control. 3D visualization and analyses were performed using open-source program, Drishti. Cephalometric measurements were made based on selected craniofacial landmarks. Comparisons were made between sl/sl rats and the control group, which consisted of wild-type and heterozygotes. Results: Subtle reductions in facial measurements were seen in sl/sl rats when compared with the control group, ranging from 1.4% to 15%. These changes were observed in cranial, maxillary and mandibular parameters: total skull length, nasal length, nasal width, nasal cavity width, interorbital width, interlens distance, inner and outer canthal distance, maximal skull height, cranial length, intracranial length and width, interorbital width, and interzygomatic width. Consistently, craniofacial ratio indices showed sl/sl rat has a flatter cranium (skull height/skull length: 0.393 vs 0.413) and a shorter but broader nose (nasal-width/nasal-length: 0.794 vs 0.874). Additionally, subtle dystopia canthorum may be presented in sl/sl rat based on increased W index. While there was no discrepancy in dental number and morphology between the control and sl/sl groups, dimensional difference was detected. Conclusions: This study demonstrated subtle craniofacial changes are presented in ETB-/- HSCR model, supporting the idea that ETB regulates CNCC migration. The findings also implicate HSCR patient may have predisposing risks for conditions such as obstructive sleep apnea, cleft palate, or dental malocclusion. Lastly, these changes share resemblance with described domestication syndrome, supporting NCC-determining gene, ETB, may play a role in the formation of domestication.
An integrative approach to the anatomy of Syllis gracilis Grube, 1840 (Annelida) using micro-computed X-ray tomography