Evolution and development of monocot stomata.

PREMISE OF THE STUDY: Leaves of monocots are typically linear with parallel venation, though a few taxa have broad leaves. Studies of stomatal patterning and development in monocots required updating in the context of rapidly improving knowledge of both the phylogenetic and development-genetic context of monocots that facilitate studies of character evolution. METHODS: We used an existing microscope-slide collection to obtain data on stomatal structure across all the major monocot clades, including some species with relatively broad leaves. In addition, we used both light and electron microscopy to study stomatal development in 16 selected species. We evaluated these data in a phylogenetic context to assess stomatal character evolution. KEY RESULTS: Mature stomatal patterning in monocots can be broadly categorized as anomocytic, paracytic-nonoblique, and paracytic/tetracytic oblique, depending on the presence, development, and arrangement of lateral subsidiary cells. Stomatal meristemoids invariably result from an asymmetric mitosis in monocots. In species where lateral subsidiary cells are present, they are perigene cells. Among monocots with relatively broad leaves, stomatal orientation is linear-axial in most taxa, but transverse in Lapageria and Stemona, and random in Dioscorea and some Araceae. Amplifying divisions are apparently absent in monocots. CONCLUSIONS: Anomocytic stomata represent the likely ancestral (plesiomorphic) condition in monocots, though multiple evolutionary transitions and reversals have occurred. Paracytic-nonoblique stomata with highly modified perigene lateral neighbor cells characterize grasses and other Poales. The presence of anomocytic stomata in Japonolirion and Tofieldia reinforces the concept that these two genera have retained many ancestral monocot features and are critical in understanding character evolution in monocots.

Functional linkage of gene fusions to cancer cell fitness assessed by pharmacological and CRISPR-Cas9 screening.

Many gene fusions are reported in tumours and for most their role remains unknown. As fusions are used for diagnostic and prognostic purposes, and are targets for treatment, it is crucial to assess their function in cancer. To systematically investigate the role of fusions in tumour cell fitness, we utilized RNA-sequencing data from 1011 human cancer cell lines to functionally link 8354 fusion events with genomic data, sensitivity to >350 anti-cancer drugs and CRISPR-Cas9 loss-of-fitness effects. Established clinically-relevant fusions were identified. Overall, detection of functional fusions was rare, including those involving cancer driver genes, suggesting that many fusions are dispensable for tumour fitness. Therapeutically actionable fusions involving RAF1, BRD4 and ROS1 were verified in new histologies. In addition, recurrent YAP1-MAML2 fusions were identified as activators of Hippo-pathway signaling in multiple cancer types. Our approach discriminates functional fusions, identifying new drivers of carcinogenesis and fusions that could have clinical implications.