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BackgroundMethanogens that populate the gastrointestinal tract of livestock ruminants contribute significantly to methane emissions from the agriculture industry. There is a great need to analyze archaeal microbiomes from a broad range of host species in order to establish causal relationships between the structure of methanogen communities and their potential for methane emission. In this report, we present an investigation of methanogenic archaeal populations in the foregut of alpacas.ResultsWe constructed individual 16S rRNA gene clone libraries from five sampled animals and recovered a total of 947 sequences which were assigned to 51 species-level OTUs. Individuals were found to each have between 21 and 27 OTUs, of which two to six OTUs were unique. As reported in other host species, Methanobrevibacter was the dominant genus in the alpaca, representing 88.3% of clones. However, the alpaca archaeal microbiome was different from other reported host species, as clones showing species-level identity to Methanobrevibacter millerae were the most abundant.ConclusionFrom our analysis, we propose a model to describe the population structure of Methanobrevibacter-related methanogens in the alpaca and in previously reported host species, which may contribute in unraveling the complexity of symbiotic archaeal communities in herbivores.

The trophoblast cell lineage is an interesting model system because it is composed of a limited number of cell types that are spatially patterned. Trophoblast stem (TS) cells reside within a layer called the chorion and either remain as stem cells or differentiate into spongiotrophoblast (SpT), trophoblast giant (TG) cells or syncytiotrophoblast cells (SynT) of the labyrinth. Maintenance of the TS phenotype is dependent on stimulation by FGF4, whereas differentiation and/or maintenance of the differentiated derivatives are dependent on key transcription factors: Mash2 for SpT, Hand1 for TG cells and Gcm1 for SynT cells. TS cells proliferate and retain their stem cell phenotype in culture in response to FGF4 and an additional factor(s) that can be provided by conditioned medium from embryonic fibroblast feeder cells (CM). To understand the functions of Hand1, Mash2 and Gcm1 at a cellular level, we tested the effects of their ectopic and over-expression on the ability of TS cells to either continue to proliferate or differentiate into their alternative fates. Expression of Mash2 alone had no effects on TS cell differentiation. However, Mash2-transfected cells continued to divide longer after withdrawal of FGF/CM. Hand1 promoted TGC differentiation, even in the continued presence of FGF4/CM. Stra13, another bHLH factor gene that is expressed in TG cells, also induced TG differentiation. Gcm1 induced a rapid arrest of TS proliferation but, in contrast to Hand1 and Stra13, blocked TG cell differentiation. Although Gcm1 was not sufficient to promote SynT formation, expression of an antisense Gcm1 transcript blocked SynT differentiation. These data suggest that Mash2 functions to promote transient FGF4-independent amplification of trophoblast cells that are progressing towards the SpT and TG cell phenotype. By contrast, Hand1 and Stra13 promote cell cycle exit and restrict cells towards the TG fate, whereas Gcm1 promotes cell cycle exit and restriction towards the SynT fate.

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