Dataset Information

Attenuated Fgf Signaling Underlies the Forelimb Heterochrony in the Emu Dromaius novaehollandiae.

ABSTRACT: Powered flight was fundamental to the establishment and radiation of birds. However, flight has been lost multiple times throughout avian evolution. Convergent losses of flight within the ratites (flightless paleognaths, including the emu and ostrich) often coincide with reduced wings. Although there is a wealth of anatomical knowledge for several ratites, the genetic mechanisms causing these changes remain debated. Here, we use a multidisciplinary approach employing embryological, genetic, and genomic techniques to interrogate the mechanisms underlying forelimb heterochrony in emu embryos. We show that the initiation of limb formation, an epithelial to mesenchymal transition (EMT) in the lateral plate mesoderm (LPM) and myoblast migration into the LPM, occur at equivalent stages in the emu and chick. However, the emu forelimb fails to subsequently proliferate. The unique emu forelimb expression of Nkx2.5, previously associated with diminished wing development, initiates after this stage (concomitant with myoblast migration into the LPM) and is therefore unlikely to cause this developmental delay. In contrast, RNA sequencing of limb tissue reveals significantly lower Fgf10 expression in the emu forelimb. Artificially increasing Fgf10 expression in the emu LPM induces ectodermal Fgf8 expression and a limb bud. Analyzing open chromatin reveals differentially active regulatory elements near Fgf10 and Sall-1 in the emu wing, and the Sall-1 enhancer activity is dependent on a likely Fgf-mediated Ets transcription factor-binding site. Taken together, our results suggest that regulatory changes result in lower expression of Fgf10 and a concomitant failure to express genes required for limb proliferation in the early emu wing bud.

SUBMITTER: Young JJ

PROVIDER: S-EPMC6834345 | biostudies-literature | 2019 Nov

REPOSITORIES: biostudies-literature

ACCESS DATA

Publications

Attenuated Fgf Signaling Underlies the Forelimb Heterochrony in the Emu Dromaius novaehollandiae.

Young John J JJ Grayson Phil P Edwards Scott V SV Tabin Clifford J CJ

Current biology : CB 20191024 21

Powered flight was fundamental to the establishment and radiation of birds. However, flight has been lost multiple times throughout avian evolution. Convergent losses of flight within the ratites (flightless paleognaths, including the emu and ostrich) often coincide with reduced wings. Although there is a wealth of anatomical knowledge for several ratites, the genetic mechanisms causing these changes remain debated. Here, we use a multidisciplinary approach employing embryological, genetic, and ...[more]

PMID: 31668620

Similar Datasets

Project description:The evolutionary origin of powered flight was fundamental to the establishment and radiation of the avian clade, and it remains a salient feature of modern birds. However, flight has been lost multiple times throughout the evolution of the avian lineage. Ratites (flightless palaeognaths, including the emu, ostrich and other well-known groups) are perhaps the most notable flightless birds, and their convergent losses of flight often coincide with adaptations to a cursorial lifestyle, including robust legs, digit loss, and reduced wings. Although there is a wealth of comparative anatomical knowledge for several ratites, the underlying genetic mechanisms producing these changes remain debated. Here we use a multidisciplinary approach employing embryological, genetic, and genomic techniques to interrogate the mechanisms underlying the delay in forelimb development contributing to the diminution of the forelimb in emu embryos. We show that the epithelial to mesenchymal transition (EMT) in the lateral plate mesoderm (LPM) and muscle precursor migration, the initiating events of limb formation, occur at equivalent stages in the emu and chick. However, the early emu forelimb fails to proliferate at HH18. The unique emu forelimb expression of Nkx2.5, previously associated with diminished wing development, does not initiate until after this stage, concomitant with migration of myoblasts into the limb bud, and hence would not appear to be the proximal cause of limb reduction in this species. In contrast, RNA-sequencing of HH18 limb tissues reveals significantly lower Fgf10 expression in the emu forelimb. Artificially increasing mesenchymal Fgf10 expression to the nascent emu wing induces ectodermal Fgf8 expression and results in a proliferative limb bud. Analyzing open chromatin reveals differentially active regulatory elements near Fgf10 and Sall-1 in the emu wing compared to emu hindlimb and both chicken limbs. Additionally, we show that the Sall-1 enhancer activity is dependent on an Ets transcription factor-binding site likely mediated by Fgf-signaling. Taken together, our results support a model where regulatory changes result in lower expression of Fgf10 and a concomitant failure to induce the genes required for limb proliferation in the early emu wing bud at HH18.

Project description:Emus (Dromaius novaehollandiae), a large flightless omnivorous ratite, are farmed for their fat and meat. Emu fat can be rendered into oil for therapeutic and cosmetic use. They are capable of gaining a significant portion of its daily energy requirement from the digestion of plant fibre. Despite of its large body size and low metabolic rate, emus have a relatively simple gastroinstetinal (GI) tract with a short mean digesta retention time. However, little is known about the GI microbial diversity of emus. The objective of this study was to characterize the intraluminal intestinal bacterial community in the different segments of small intestine (duodenum, jejunum, and ileum) using pyrotag sequencing and compare that with the ceca. Gut content samples were collected from each of four adult emus (2 males, 2 females; 5-6 years old) that were free ranged but supplemented with a barley-alfalfa-canola based diet. We amplified the V3-V5 region of 16S rRNA gene to identify the bacterial community using Roche 454 Junior system. After quality trimming, a total of 165,585 sequence reads were obtained from different segments of the small intestine (SI). A total of 701 operational taxonomic units (OTUs) were identified in the different segments of small intestine. Firmicutes (14-99%) and Proteobacteria (0.5-76%) were the most predominant bacterial phyla in the small intestine. Based on species richness estimation (Chao1 index), the average number of estimated OTUs in the small intestinal compartments were 148 in Duodenum, 167 in Jejunum, and 85 in Ileum, respectively. Low number of core OTUs identified in each compartment of small intestine across individual birds (Duodenum: 13 OTUs, Jejunum: 2 OTUs, Ileum: 14 OTUs) indicated unique bacterial community in each bird. Moreover, only 2 OTUs (Escherichia and Sinobacteraceae) were identified as core bacteria along the whole small intestine. PICRUSt analysis has indicated that the detoxification of plant material and environmental chemicals seem to be performed by SI microbiota, especially those in the jejunum. The emu cecal microbiome has more genes than SI segments involving in protective or immune response to enteric pathogens. Microbial digestion and fermentation is mostly in the jejunum and ceca. This is the first study to characterize the microbiota of different compartments of the emu intestines via gut samples and not fecal samples. Results from this study allow us to further investigate the influence of the seasonal and physiological changes of intestinal microbiota on the nutrition of emus and indirectly influence the fatty acid composition of emu fat.

Dataset Information

Attenuated Fgf Signaling Underlies the Forelimb Heterochrony in the Emu Dromaius novaehollandiae.

Publications

Attenuated Fgf Signaling Underlies the Forelimb Heterochrony in the Emu Dromaius novaehollandiae.

Similar Datasets

OmicsDI is part of the ELIXIR infrastructure

Tweets