Phenotypic cross-species conservation and cross-generation directionality switching in epigenetic inheritance.

Evidence supporting non-DNA sequence-based inheritance in animals has increasingly been described in recent years, often under intergenerational inheritance or transgenerational epigenetic inheritance (TEI). Existence of the latter, a stronger indicator of germline transmission, has been demonstrated in invertebrates and mammals alike. The mechanisms and physiological implications of TEI, however, remain unclear. Here, in an unbiased approach, we compared existing transcriptomic data associated with so far available Drosophila models of inter- and trans-, and rodent models of inter-generational inheritance; observed phenotypic cross-species conservation and cross-generation directionality shift therein; and confirmed these observations experimentally in flies. Specifically, previous models of cold and diet-induced inheritance in both flies and mice were commonly associated with altered regulation of proteolysis genes. Besides, fly TEI models were in general characterized by opposite phenotypic regulation in transgenerational offsprings, compared to the ancestors. As insulin-producing cell (IPC) ablation was also associated with proteolysis gene dysregulation in one of the mouse models, we opted to use genetic ablation of IPCs in flies for the experimental validation. Remarkably, the ablation led to transcriptomic alterations across multiple generations, with dysregulated genes showing proteolysis enrichment. Similarly, phenotypic directionality changed in the opposite direction in transgenerational offsprings, in comparison of the ancestors. These results support evolutionary conservation, and both physiologically adaptive and maladaptive consequences of germline mediated epigenetic inheritance.

Paternal inheritance of diet induced metabolic traits correlates with germline regulation of diet induced coding gene expression.

Inheritance of induced traits through the germline is poorly understood and controversial. The ideal evidence correlating induced and inherited traits with germline gene expression remains largely obscure. Using a Drosophila coding transcriptome level model of paternal high sugar diet induced alterations in triglyceride levels across generations, in conjunction with pre-existing data, we show here highly significant overlap of differentially expressed genes between the ancestral generation, the resulting sperm and embryos, and the future generation individuals. Further, gene ontology and literature-wide overrepresentation analysis reveal association of lipid and carbohydrate metabolism, and immune response, besides others, with differentially expressed genes in the above samples. Analysis of available mouse data on inheritance of diet induced metabolic traits also revealed a similar correlation. Our results support a causal role of sperm borne mRNAs in inheritance of acquired characteristics, consistent with the evidence that these mRNAs are delivered to the oocyte and influence embryonic development.

Transgenerational inheritance of cold temperature response in Drosophila.

Intergenerational inheritance of transcriptional responses induced by low temperature rearing has recently been shown in Drosophila. Besides germline inheritance, fecal transfer experiments indirectly suggested that the acquired microbiome may also have contributed to the transcriptional responses in offspring. Here, we analyze expression data on inheritance of the cold-induced effects in conjunction with previously reported transcriptomic differences between flies with a microbiota or axenic flies and provide support for a contribution of the acquired microbiome to the offspring phenotype. Also, based on a similar analysis in conjunction with diet- and metabolism-related fly transcriptome data, we predicted and, then, experimentally confirmed that cold regulates triglyceride levels both inter- as well as trans-generationally.