Human facial diversity is substantial, complex, and largely scientifically unexplained. We used spatially dense quasi-landmarks to measure face shape in population samples with mixed West African and European ancestry from three locations (United States, Brazil, and Cape Verde). Using bootstrapped response-based imputation modeling (BRIM), we uncover the relationships between facial variation and the effects of sex, genomic ancestry, and a subset of craniofacial candidate genes. The facial effects of these variables are summarized as response-based imputed predictor (RIP) variables, which are validated using self-reported sex, genomic ancestry, and observer-based facial ratings (femininity and proportional ancestry) and judgments (sex and population group). By jointly modeling sex, genomic ancestry, and genotype, the independent effects of particular alleles on facial features can be uncovered. Results on a set of 20 genes showing significant effects on facial features provide support for this approach as a novel means to identify genes affecting normal-range facial features and for approximating the appearance of a face from genetic markers.

Bacteria exist in a variety of morphologies, but the relationship between cellular forms and biological functions remains poorly understood. We show that stalks (prosthecae), cylindrical extensions of the Caulobacter crescentus cell envelope, can take up and hydrolyze organic phosphate molecules and contain the highaffinity phosphate-binding protein PstS, but not PstA, a protein that is required for transport of phosphate into the cytoplasm. Therefore, uptake, hydrolysis, and periplasmic binding of a phosphate source can take place in the stalk, but high-affinity import must take place in the cell body. Furthermore, by using analytical modeling, we illustrate the biophysical advantage of the stalk as a morphological adaptation to the diffusion-limited, oligotrophic environments where C. crescentus thrives. This advantage is due to the fact that a stalk is long and thin, a favorable shape for maximizing contact with diffusing nutrients while minimizing increases in both surface area and cell volume.acteria exhibit an amazing diversity of shapes and sizes. Bacterial cells can be round, cylindrical, curved, or coiled. Some are shaped like a flat square, others like a star; some are branched, and some have projections of the cell surface. Exactly how bacterial shapes are generated is not known, and the purposes of a specific cell shape are not always clear. Yet, in most cases, specific shapes are precisely reproduced at every generation. Cell shape changes can also occur during the life cycle of many bacterial species, such as the transformation of Sinorhizobium from rods to branched cells (Y forms) after colonization of legume root nodules. Although these morphological transformations are thought to play important roles in the life cycles of bacteria, the advantages of cell shape changes remain essentially speculative (1).Here, we investigate the function of prosthecae, cell envelope extensions that are present in a morphologically diverse group of Gram-negative bacteria (2). Unlike flagella or pili, prosthecae are true extensions of the cell proper, possessing both peptidoglycan and cell membranes. In the aquatic bacterium Caulobacter crescentus, prosthecae are referred to as stalks. The function of Caulobacter stalks is not known, but one common hypothesis is that they facilitate the acquisition of nutrients from the environment (3, 4). This hypothesis is consistent with the observation that stalks dramatically elongate under phosphate starvation conditions, with the capacity to reach lengths of Ͼ30 m (5, 6), a length that is approximately equivalent to that of 15 cell bodies. We show that the stalk of C. crescentus (Fig. 1A) can transport a nutrient molecule from the extracellular space into its periplasm and that the stalk constitutes a biophysically efficient morphological adaptation to environments where nutrient uptake is limited by diffusion. Results Stalks Can Take Up and Hydrolyze Fluorescein Diphosphate (FDP).To determine whether stalks are capable of nutrient uptake, we incubated cells with FDP, a fluor...

SummaryHow cells maintain their ploidy is relevant to cellular development and disease. Here, we investigate the mechanism by which the bacterium Bacillus subtilis enforces diploidy as it differentiates into a dormant spore. We demonstrate that a sporulation-induced protein SirA (originally annotated YneE) blocks new rounds of replication by targeting the highly conserved replication initiation factor DnaA. We show that SirA interacts with DnaA and displaces it from the replication origin. As a result, expression of SirA during growth rapidly blocks replication and causes cell death in a DnaA-dependent manner. Finally, cells lacking SirA over-replicate during sporulation. These results support a model in which induction of SirA enforces diploidy by inhibiting replication initiation as B. subtilis cells develop into spores.