Functional divergence of the bag of marbles gene in the Drosophila melanogaster species group

The combination of recent advances in both genomic and gene editing technologies have opened up new possibilities for assessing the functional consequences and drivers of positive selection. In Drosophila melanogaster, a key germline stem cell differentiation factor, bag of marbles (bam) shows rapid bursts of amino acid fixations between its D. melanogaster and its sibling species D. simulans, but not in the outgroup species D. ananassae. We previously hypothesized that a genetic conflict with the maternally inherited, intracellular bacteria W. pipientis could be driving the adaptive evolution of bam as W. pipientis increases the fertility of a bam partial loss of function mutant. However, we have not been able to further test this hypothesis by assessing bam variation in other Drosophila lineages and their interactions with W. pipientis because bam function has not been examined in non-melanogaster Drosophila species. Since bam is rapidly evolving at the protein level, its function may not be conserved between species, and therefore different evolutionary pressures may be shaping bam in individual lineages. Here, we ask if bam is necessary for GSC daughter differentiation in five Drosophila species in the melanogaster species group that span approximately 15 million years of divergence and show different patterns of nucleotide sequence evolution at bam. We find that bam function is not fully conserved across these species, and that bam function may change on a relatively short time scale. Ultimately, we conclude that a simple gain in function as the germline stem cell differentiation factor alone does not explain our population genetic and functional genetic results we have observed. Our findings provide a foundation on which to explore the evolution of bam as a GSC differentiation factor and its interactions with W. pipientis in specific lineages.

12-O-Tetradecanoylphorbol-13-acetate increases cardiomyogenesis through PKC/ERK signaling

12-O-Tetradecanoylphorbol-13-acetate (TPA) is the most widely used diacylglycerol (DAG) mimetic agent and inducer of protein kinase C (PKC)-mediated cellular response in biomedical studies. TPA has been proposed as a pluripotent cell differentiation factor, but results obtained have been inconsistent. In the present study we show that TPA can be applied as a cardiomyogenesis-promoting factor for the differentiation of mouse embryonic stem (mES) cells in vitro. The mechanism of TPA action is mediated by the induction of extracellular signal-regulated kinase (ERK) activity and the subsequent phosphorylation of GATA4 transcription factor. Interestingly, general mitogens (FGF, EGF, VEGF and serum) or canonical WNT signalling did not mimic the effect of TPA. Moreover, on the basis of our results, we postulate that a TPA-sensitive population of cardiac progenitor cells exists at a certain time point (after days 6–8 of the differentiation protocol) and that the proposed treatment can be used to increase the multiplication of ES cell-derived cardiomyocytes.

The embryonic transcription factor Hlxb9 is a menin interacting partner that controls pancreatic β-cell proliferation and the expression of insulin regulators

The multiple endocrine neoplasia type 1 (MEN1) syndrome is caused by germline mutations in the MEN1 gene encoding menin, with tissue-specific tumors of the parathyroids, anterior pituitary, and enteropancreatic endocrine tissues. Also, 30–40% of sporadic pancreatic endocrine tumors show somatic MEN1 gene inactivation. Although menin is expressed in all cell types of the pancreas, mouse models with loss of menin in either pancreatic α-cells, or β-cells, or total pancreas develop β-cell-specific endocrine tumors (insulinomas). Loss of widely expressed tumor suppressor genes may produce tissue-specific tumors by reactivating one or more embryonic-specific differentiation factors. Therefore, we determined the effect of menin overexpression or knockdown on the expression of β-cell differentiation factors in a mouse β-cell line (MIN6). We show that the β-cell differentiation factor Hlxb9 is posttranscriptionally upregulated upon menin knockdown, and it interacts with menin. Hlxb9 reduces cell proliferation and causes apoptosis in the presence of menin, and it regulates genes that modulate insulin level. Thus, upon menin loss or from other causes, dysregulation of Hlxb9 predicts a possible combined mechanism for β-cell proliferation and insulin production in insulinomas. These observations help to understand how a ubiquitously expressed protein such as menin might control tissue-specific tumorigenesis. Also, our findings identify Hlxb9 as an important factor for β-cell proliferation and insulin regulation.