A few genetic variants go a long way in differentiating <i>Penstemon</i> species
by Yaniv Brandvain, Shelley SiantaThe integrity of hybridizing species is usually maintained by genome-wide selection or by selection on a few genomic regions. A study published in PLOS Biology finds a different pattern—60 SNPs spread across the genome differentiate a Penstemon species pair. Hybridizing species are usually maintained by genome-wide selection against introgression or by selection on a few “genomic islands”. This Primer explores the implications of a study which finds a new pattern – 60 SNPs spread across the genome differentiate Penstemon species with different pollinators.
Opposing action of the FLR-2 glycoprotein hormone and DRL-1/FLR-4 MAP kinases balance p38-mediated growth and lipid homeostasis in <i>C</i>. <i>elegans</i>
by Sarah K. Torzone, Aaron Y. Park, Peter C. Breen, Natalie R. Cohen, Robert H. DowenAnimals integrate developmental and nutritional signals before committing crucial resources to growth and reproduction; however, the pathways that perceive and respond to these inputs remain poorly understood. Here, we demonstrate that DRL-1 and FLR-4, which share similarity with mammalian mitogen-activated protein kinases, maintain lipid homeostasis in the C. elegans intestine. DRL-1 and FLR-4 function in a protein complex at the plasma membrane to promote development, as mutations in drl-1 or flr-4 confer slow growth, small body size, and impaired lipid homeostasis. To identify factors that oppose DRL-1/FLR-4, we performed a forward genetic screen for suppressors of the drl-1 mutant phenotypes and identified mutations in flr-2 and fshr-1, which encode the orthologues of follicle stimulating hormone and its putative G protein–coupled receptor, respectively. In the absence of DRL-1/FLR-4, neuronal FLR-2 acts through intestinal FSHR-1 and protein kinase A signaling to restrict growth. Furthermore, we show that opposing signaling through DRL-1 and FLR-2 coordinates TIR-1 oligomerization, which modulates downstream p38/PMK-1 activity, lipid homeostasis, and development. Finally, we identify a surprising noncanonical role for the developmental transcription factor PHA-4/FOXA in the intestine where it restricts growth in response to impaired DRL-1 signaling. Our work uncovers a complex multi-tissue signaling network that converges on p38 signaling to maintain homeostasis during development.
A few essential genetic loci distinguish <i>Penstemon</i> species with flowers adapted to pollination by bees or hummingbirds
by Carolyn A. Wessinger, Amanda M. Katzer, Paul M. Hime, Mark D. Rausher, John K. Kelly, Lena C. HilemanIn the formation of species, adaptation by natural selection generates distinct combinations of traits that function well together. The maintenance of adaptive trait combinations in the face of gene flow depends on the strength and nature of selection acting on the underlying genetic loci. Floral pollination syndromes exemplify the evolution of trait combinations adaptive for particular pollinators. The North American wildflower genus Penstemon displays remarkable floral syndrome convergence, with at least 20 separate lineages that have evolved from ancestral bee pollination syndrome (wide blue-purple flowers that present a landing platform for bees and small amounts of nectar) to hummingbird pollination syndrome (bright red narrowly tubular flowers offering copious nectar). Related taxa that differ in floral syndrome offer an attractive opportunity to examine the genomic basis of complex trait divergence. In this study, we characterized genomic divergence among 229 individuals from a Penstemon species complex that includes both bee and hummingbird floral syndromes. Field plants are easily classified into species based on phenotypic differences and hybrids displaying intermediate floral syndromes are rare. Despite unambiguous phenotypic differences, genome-wide differentiation between species is minimal. Hummingbird-adapted populations are more genetically similar to nearby bee-adapted populations than to geographically distant hummingbird-adapted populations, in terms of genome-wide dXY. However, a small number of genetic loci are strongly differentiated between species. These approximately 20 “species-diagnostic loci,” which appear to have nearly fixed differences between pollination syndromes, are sprinkled throughout the genome in high recombination regions. Several map closely to previously established floral trait quantitative trait loci (QTLs). The striking difference between the diagnostic loci and the genome as whole suggests strong selection to maintain distinct combinations of traits, but with sufficient gene flow to homogenize the genomic background. A surprisingly small number of alleles confer phenotypic differences that form the basis of species identity in this species complex.
Computational and systems neuroscience: The next 20 years
by Christopher Summerfield, Kevin MillerOver the past 20 years, neuroscience has been propelled forward by theory-driven experimentation. We consider the future outlook for the field in the age of big neural data and powerful artificial intelligence models. What does the future of neuroscience look like in the age of big neural data and advanced AI models. In this Perspective, the authors advocate for new approaches that combine the merits of data-driven model discovery and hypothesis-driven model comparison.
Rapid mechanosensitive migration and dispersal of newly divided mesenchymal cells aid their recruitment into dermal condensates
by Jon Riddell, Shahzeb Raja Noureen, Luigi Sedda, James D. Glover, William K. W. Ho, Connor A. Bain, Arianna Berbeglia, Helen Brown, Calum Anderson, Yuhang Chen, Michael L. Crichton, Christian A. Yates, Richard L. Mort, Denis J. HeadonEmbryonic mesenchymal cells are dispersed within an extracellular matrix but can coalesce to form condensates with key developmental roles. Cells within condensates undergo fate and morphological changes and induce cell fate changes in nearby epithelia to produce structures including hair follicles, feathers, or intestinal villi. Here, by imaging mouse and chicken embryonic skin, we find that mesenchymal cells undergo much of their dispersal in early interphase, in a stereotyped process of displacement driven by 3 h of rapid and persistent migration followed by a long period of low motility. The cell division plane and the elevated migration speed and persistence of newly born mesenchymal cells are mechanosensitive, aligning with tissue tension, and are reliant on active WNT secretion. This behaviour disperses mesenchymal cells and allows daughters of recent divisions to travel long distances to enter dermal condensates, demonstrating an unanticipated effect of cell cycle subphase on core mesenchymal behaviour.