Lateral cell polarization drives organization of epithelia in sea anemone embryos and embryonic cell aggregates.

One of the first organizing processes during animal development is the assembly of embryonic cells into epithelia. In certain animals, including Hydra and sea anemones, epithelia also emerge when cells from dissociated tissues are aggregated back together. Although cell adhesion is required to keep cells together, it is not clear whether cell polarization plays a role as epithelia emerge from disordered aggregates. Here, we demonstrate that lateral cell polarization is essential for epithelial organization in both embryos and aggregates of the sea anemone Nematostella vectensis. Specifically, knock down of the lateral polarity protein Lgl disrupts epithelia in developing embryos and impairs the capacity of dissociated cells to epithelialize from aggregates. Cells in lgl mutant epithelia lose their columnar shape and have mispositioned mitotic spindles and ciliary basal bodies. Together, our data suggest that in Nematostella, Lgl is required to establish lateral cell polarity and position cytoskeletal organelles in cells of embryos and aggregates during de novo epithelial organization.

Draft genome assemblies of four manakins.

Manakins are a family of small suboscine passerine birds characterized by their elaborate courtship displays, non-monogamous mating system, and sexual dimorphism. This family has served as a good model for the study of sexual selection. Here we present genome assemblies of four manakin species, including Cryptopipo holochlora, Dixiphia pipra (also known as Pseudopipra pipra), Machaeropterus deliciosus and Masius chrysopterus, generated by Single-tube Long Fragment Read (stLFR) technology. The assembled genome sizes ranged from 1.10 Gb to 1.19 Gb, with average scaffold N50 of 29 Mb and contig N50 of 169 Kb. On average, 12,055 protein-coding genes were annotated in the genomes, and 9.79% of the genomes were annotated as repetitive elements. We further identified 75 Mb of Z-linked sequences in manakins, containing 585 to 751 genes and an ~600 Kb pseudoautosomal region (PAR). One notable finding from these Z-linked sequences is that a possible Z-to-autosome/PAR reversal could have occurred in M. chrysopterus. These de novo genomes will contribute to a deeper understanding of evolutionary history and sexual selection in manakins.

Canalized gene expression during development mediates caste differentiation in ants.

Ant colonies are higher-level organisms consisting of specialized reproductive and non-reproductive individuals that differentiate early in development, similar to germ-soma segregation in bilateral Metazoa. Analogous to diverging cell lines, developmental differentiation of individual ants has often been considered in epigenetic terms but the sets of genes that determine caste phenotypes throughout larval and pupal development remain unknown. Here, we reconstruct the individual developmental trajectories of two ant species, Monomorium pharaonis and Acromyrmex echinatior, after obtaining >1,400 whole-genome transcriptomes. Using a new backward prediction algorithm, we show that caste phenotypes can be accurately predicted by genome-wide transcriptome profiling. We find that caste differentiation is increasingly canalized from early development onwards, particularly in germline individuals (gynes/queens) and that the juvenile hormone signalling pathway plays a key role in this process by regulating body mass divergence between castes. We quantified gene-specific canalization levels and found that canalized genes with gyne/queen-biased expression were enriched for ovary and wing functions while canalized genes with worker-biased expression were enriched in brain and behavioural functions. Suppression in gyne larvae of Freja, a highly canalized gyne-biased ovary gene, disturbed pupal development by inducing non-adaptive intermediate phenotypes between gynes and workers. Our results are consistent with natural selection actively maintaining canalized caste phenotypes while securing robustness in the life cycle ontogeny of ant colonies.

The Mutationathon highlights the importance of reaching standardization in estimates of pedigree-based germline mutation rates.

In the past decade, several studies have estimated the human per-generation germline mutation rate using large pedigrees. More recently, estimates for various nonhuman species have been published. However, methodological differences among studies in detecting germline mutations and estimating mutation rates make direct comparisons difficult. Here, we describe the many different steps involved in estimating pedigree-based mutation rates, including sampling, sequencing, mapping, variant calling, filtering, and appropriately accounting for false-positive and false-negative rates. For each step, we review the different methods and parameter choices that have been used in the recent literature. Additionally, we present the results from a 'Mutationathon,' a competition organized among five research labs to compare germline mutation rate estimates for a single pedigree of rhesus macaques. We report almost a twofold variation in the final estimated rate among groups using different post-alignment processing, calling, and filtering criteria, and provide details into the sources of variation across studies. Though the difference among estimates is not statistically significant, this discrepancy emphasizes the need for standardized methods in mutation rate estimations and the difficulty in comparing rates from different studies. Finally, this work aims to provide guidelines for computational and statistical benchmarks for future studies interested in identifying germline mutations from pedigrees.