Biology subjects

Bravo, P.

Publications and source records attributed to Bravo, P..

4 recordsLinked to original sources

bioRxiv2023

Examining the role of oxygen-binding proteins on the early evolution of multicellularity

Oxygen availability is a key factor in the evolution of multicellularity, as larger and more sophisticated organisms often require mechanisms allowing efficient oxygen delivery to their tissues. One such mechanism is the presence of oxygen-binding proteins, such as globins and hemerythrins, which arose in the ancestor of bilaterian animals. Despite their importance, the precise mechanisms by which oxygen-binding proteins influenced the early stages of multicellular evolution under varying environmental oxygen levels are not yet clear. We addressed this knowledge gap by heterologously expressing the oxygen binding proteins myoglobin and myohemerythrin in snowflake yeast, a model system of simple, undifferentiated multicellularity. These proteins increased the depth and rate of oxygen diffusion, increasing the fitness of snowflake yeast growing aerobically. Experiments show that, paradoxically, oxygen-binding proteins confer a greater fitness benefit for larger organisms under high, not low, O2 conditions. We show via biophysical modeling that this is because facilitated diffusion is more efficient when oxygen is abundant, transporting a greater quantity of O2 which can be used for metabolism. By alleviating anatomical diffusion limitations to oxygen consumption, the evolution of O2-binding proteins in the oxygen-rich Neoproterozoic may have been a key breakthrough enabling the evolution of increasingly large, complex multicellular metazoan lineages.

evolutionary biology↗

bioRxiv2023

Emergence and maintenance of stable coexistence during a long-term multicellular evolution experiment

The evolution of multicellular life spurred evolutionary radiations, fundamentally changing many of Earths ecosystems. Yet little is known about how early steps in the evolution of multicellularity transform eco-evolutionary dynamics, e.g., via niche expansion processes that may facilitate coexistence. Using long-term experimental evolution in the snowflake yeast model system, we show that the evolution of multicellularity drove niche partitioning and the adaptive divergence of two distinct, specialized lineages from a single multicellular ancestor. Over 715 daily transfers, snowflake yeast were subject to selection for rapid growth in rich media, followed by selection favoring larger group size. Both small and large cluster-forming lineages evolved from a monomorphic ancestor, coexisting for over ~4,300 generations. These small and large sized snowflake yeast lineages specialized on divergent aspects of a trade-off between growth rate and survival, mirroring predictions from ecological theory. Through modeling and experimentation, we demonstrate that coexistence is maintained by a trade-off between organismal size and competitiveness for dissolved oxygen. Taken together, this work shows how the evolution of a new level of biological individuality can rapidly drive adaptive diversification and the expansion of a nascent multicellular niche, one of the most historically-impactful emergent properties of this evolutionary transition.

evolutionary biology↗

bioRxiv2023

Macrophage activation drives ovarian failure and masculization

In humans, premature ovarian insufficiency (POI) is caused by autoimmunity and genetic factors, such as mutation of BMP15, a key ovarian determining gene. The cellular mechanisms associated with ovarian failure caused by BMP15 mutation and immune contributions to the disorder are not understood. BMP15s role in ovarian follicle development is conserved in vertebrates, including zebrafish. Using zebrafish, we established a causal link between macrophage activation and ovarian failure. We identified a germline-somatic gonadal cell-macrophage axis underlying ovarian atresia. Germline loss of Bmp15 triggers this axis that single-cell RNA sequencing and genetic analyses indicate involves activation of ovarian somatic cells that express conserved macrophage-activating ligands. Genetic ablation of macrophages blocks premature oocyte loss. Thus, the axis identified here represents potential therapeutic targets to preserve female fertility. One-Sentence SummarySex reversal due to Bmp15 deficiency requires macrophage activation by Csf1a, which is expressed by specialized pre-follicle cells in zebrafish.

developmental biology↗

bioRxiv2022

Vertical growth dynamics of biofilms

During the biofilm life cycle, bacteria attach to a surface then reproduce, forming crowded, growing communities. Many theoretical models of biofilm growth dynamics have been proposed; however, difficulties in measuring biofilm height accurately across relevant time and length scales have prevented testing these models or their biophysical underpinnings empirically. Using white light interferometry, we measure the heights of microbial colonies with nanometer precision from inoculation to their final equilibrium height, producing a novel and detailed empirical characterization of vertical growth dynamics. We show that models relying on logistic growth or nutrient depletion fail to capture biofilm height dynamics on short and long time scales. Our empirical results support a simple model inspired by the fact that biofilms only interact with the environment through their interfaces. This interface model captures the growth dynamics from short to long time scales (10 minutes to 14 days) of diverse microorganisms, including prokaryotes like gram-negative and gram-positive bacteria and eukaryotes like aerobic and anaerobic yeast. This model provides heuristic value, highlighting the biophysical constraints that limit vertical growth as well as establishing a quantitative model for biofilm development.

biophysics↗