We investigate with Robert J. Asher (University of Cambridge) on heterochrony of skeletal ossification in Afrotheria and we collaborate with Denis Duboule (University of Geneva) on a study of transcriptional regulation of Hoxd genes during caecum budding in mammals.
Consensus on placental mammal phylogeny enables investigation into the possibility that placental clades differ from one another in terms of their development. We focus on the sequence of skeletal ossification as a possible source of developmental distinctiveness between the two major clades. We contribute data on cranial and postcranial ossification events during growth in Afrotheria, including elephants, hyraxes, golden moles, tenrecs, sengis, and aardvarks. We show that afrotherians significantly differ from other placentals by an early ossification of some skeletal elements. Our analysis also suggests that southern placental groups show a greater degree of developmental variability.
Hox genes are required for the development of the intestinal cecum, a major organ of plant-eating species. We have analyzed the transcriptional regulation of Hoxd genes in cecal buds and show that they are controlled by a series of enhancers located in a gene desert flanking the HoxD cluster. The start site of two opposite long noncoding RNAs (lncRNAs), Hotdog and Twin of Hotdog, selectively contacts the expressed Hoxd genes in the framework of a topological domain, coinciding with robust transcription of these genes during cecum budding. Both lncRNAs are specifically transcribed in the cecum, albeit bearing no detectable function in trans. Hedgehogs have kept this regulatory potential despite the absence of the cecum, suggesting that these mechanisms are used in other developmental situations. In this context, we discuss the implementation of a common ‘‘budding toolkit’’ between the cecum and the limbs.