Ernest Everett Just (1883-1941)--an early ecological developmental biologist

Increasing Diversity in Developmental Biology

The demographic profile of the scientific and biomedical workforce in the United States does not reflect the population at large (https://ncses.nsf.gov/pubs/nsf21321/data-tables; www.census.gov), raising concerns that there will be too few trained researchers in the future, the scope of research interests will not be broad enough, gaps in equity and social justice will continue to increase, and the safeguards to the integrity of the scientific enterprise could be jeopardized. To diversify the pool of scientists, the Society for Developmental Biology (SDB) developed the Choose Development! Program-a two-summer immersion for undergraduate students belonging to underrepresented (UR) populations in STEM to join the research laboratory of an established SDB member. This research-intensive experience was augmented by a multi-tier mentoring plan for each student, society-wide recognition, professional development activities and networking at national meetings. The strengths of the Choose Development! Program were leveraged to expand inclusion and outreach at the Society's leadership level, the Board of Directors (BOD), which then led to significant changes that impacted the SDB community. The cumulative outcomes of the Choose Development! Program provides evidence that community-based, long-term advocacy, and mentoring of young UR scientists is successful in retaining UR students in scientific career paths and making a scientific society more inclusive.

Developmental plasticity: re-conceiving the genotype

In recent decades, the phenotype of an organism (i.e. its traits and behaviour) has been studied as the outcome of a developmental 'programme' coded in its genotype. This deterministic view is implicit in the Modern Synthesis approach to adaptive evolution as a sorting process among genetic variants. Studies of developmental pathways have revealed that genotypes are in fact differently expressed depending on environmental conditions. Accordingly, the genotype can be understood as a repertoire of potential developmental outcomes or norm of reaction. Reconceiving the genotype as an environmental response repertoire rather than a fixed developmental programme leads to three critical evolutionary insights. First, plastic responses to specific conditions often comprise functionally appropriate trait adjustments, resulting in an individual-level, developmental mode of adaptive variation. Second, because genotypes are differently expressed depending on the environment, the genetic diversity available to natural selection is itself environmentally contingent. Finally, environmental influences on development can extend across multiple generations via cytoplasmic and epigenetic factors transmitted to progeny individuals, altering their responses to their own, immediate environmental conditions and, in some cases, leading to inherited but non-genetic adaptations. Together, these insights suggest a more nuanced understanding of the genotype and its evolutionary role, as well as a shift in research focus to investigating the complex developmental interactions among genotypes, environments and previous environments.

E. E. Just and Creativity in Science. The Importance of Diversity

Renowned biologist Ernest Everett Just (1883-1941) was an outspoken advocate for the classical embryologist's view of the cell; he believed that all the parts of the cell, but especially the cytoplasm, have important roles to play in the process of development, whereby a one-celled zygote becomes a many-celled animal. In opposition to geneticist Thomas Hunt Morgan, Just formulated a hypothesis for how the cell works in development, one that gave a more dominant role to cytoplasmic (instead of nuclear) factors. This paper argues that, in creating his hypothesis, Just applied insights from the African American intellectual community in which he was immersed, much as Charles Darwin applied insights from British political economist Thomas R. Malthus in formulating his theory of evolution by natural selection. This in no way diminishes the scientific validity of Just's (or Darwin's) hypothesis. Rather, it highlights Just's creativity and, as such, points to the importance of having diversity in science.

Ernest Everett Just: Egg and embryo as excitable systems

Ernest Everett Just (1883-1941) was an African American embryologist of international standing whose research interests lay in the area of fertilization and early development in marine invertebrates. Perhaps best known for his discovery of the dynamical and structural blocks to polyspermy that sweep over the egg upon fertilization, E. E. Just also was the first to associate cell surface changes with stages of embryonic development. He was deeply familiar with the natural history of the animals whose eggs he studied, and his knowledge of natural settings led him to emphasize the importance of using laboratory conditions that closely match those in nature. Based on more than 30 years of work, he came to believe that it was the cell surface that played the most critical role in development, heredity, and evolution. He promoted a holistic view of cells and organisms in opposition to the gene-centric view that was becoming more prevalent with the rise of genetics, but rejected the vitalism espoused by some biologists of his era, calling instead for "a physics and chemistry in a new dimension …superimposed upon the now known physics and chemistry" to account for biological phenomena. Just's incisive critique of genetic reductionism finds echoes in contemporary multiscale, systems approaches in biology. His speculations on the relationship between developmental and evolutionary mechanisms resonate with today's evolutionary developmental biology. After a brief biographical sketch, this paper outlines and discusses some of Just's scientific contributions, and shows how his ideas remain relevant today.

A century of cell adhesion: from the blastomere to the clinic part 1: conceptual and experimental foundations and the pre-molecular era

The historical roots of cell adhesion research stretch back over a hundred years, commencing with fundamental questions from the advent of experimental embryology in the late nineteenth century. The transition of embryology from a descriptive to an experimentally driven and mechanistic branch of the biological sciences included investigations focused on the interactions of the first cells of the newly developing embryo, the blastomeres, and followed the movement, interactions and fate of these cells as the tissues and organs of the growing embryo took form. Of special interest to early investigators were cell-cell contacts, which were obviously dynamic but of an obscure nature. This historical review, the first of a series, explores the early years of the cell adhesion field, including the work of Roux, Wilson, Galtsoff, Just and Holtfreter, and discusses the classical experiments, observations and conceptual developments that formed the cornerstone of cell adhesion research during its premolecular era.

In vitro follicle growth under non-attachment conditions and decreased FSH levels reduces Lhcgr expression in cumulus cells and promotes oocyte developmental competence

PURPOSE

The in-vitro environment influences oocyte competence and gene expression in cumulus cells and oocytes. Effects of culturing under non-attachment conditions and varying follicle exposure to FSH were investigated at the mRNA level and on oocyte developmental capacity.

METHODS

Quantitative PCR analysis of Gdf9, Mater, Nmp2 (in oocytes), Lhcgr and Amh (in cumulus cells), and oocyte developmental competence after in vitro follicle culture were evaluated.

RESULTS

Follicle survival (98.7%) and polar body rate (94%) were similar for all conditions. Estradiol and progesterone production were significantly lower in non-attachment follicles (10-fold and 3-fold, respectively). Under non-attachment conditions, a higher two-cell rate (69.9%) and total blastocyst yield (48.5%) were obtained and, by decreasing FSH levels during culture, Lhcgr transcripts were significantly reduced to levels similar to in-vivo. Levels of oocyte-specific transcripts were not significantly influenced by in-vitro conditions.

CONCLUSION

Non-attachment conditions influence follicle steroid secretory capacity and, together with dynamic FSH doses, positively influence cumulus cell gene expression and oocyte developmental competence.

Understanding the effects of low salinity on fertilization success and early development in the sand dollar Echinarachnius parma

Free-spawning marine invertebrates that live near shore or in estuaries may experience reduced fertilization success during low-salinity events. Although several studies have documented reproductive failure at reduced salinity in estuarine animals, few have looked at whether developmental failure is due to a failure of fertilization or to a failure of fertilized eggs to cleave. In this study, we examined the effects of salinities ranging from 18 to 32 psu on fertilization success and early development in the sand dollar Echinarachnius parma. In addition to decoupling the effects of low salinity on fertilization from its effects on early cleavage, we also assessed whether eggs or sperm were the weak link in accounting for reproductive failure. We found that both fertilization and cleavage failed at salinities below about 22 psu but that development could be partially rescued by returning zygotes to full-strength seawater. We also found that sperm remained active and capable of fertilizing eggs even after being exposed to low salinities for 30 min.. Taken together, these results suggest that reproductive failure at low salinities in E. parma is due more to an inability of the fertilized eggs to cleave than to an inability of sperm to fertilize eggs.

Ernest Everett Just, Johannes Holtfreter, and the origin of certain concepts in embryo morphogenesis

Ernest E. Just (1883-1941) is best known for his discovery of the "wave of negativity" that sweeps of the sea urchin egg during fertilization, and his elucidation of what are known as the fast and slow blocks to polyspermy. Just's contemporary Johannes Holtfreter (1901-1992) is known for his pioneering work in amphibian morphogenesis, which helped to lay the foundation for modern vertebrate developmental biology. This paper, after briefly describing the life and scientific contributions of Just, argues that his work and ideas strongly influenced two of the concepts for which Holtfreter is best known: tissue affinity and autoneuralization (or autoinduction). Specifically, this paper argues that, first, Just's experiments demonstrating developmental stage-specific changes in the adhesiveness of the blastomeres of cleavage embryos helped lay the foundation for Holtfreter's concept of tissue affinity and, second, Just's notion of the intrinsic irritability of the egg cell, which is evident in experimental parthenogenesis, strongly informed Holtfreter's concept of the nonspecific induction of neural tissue formation in amphibian gastrula ectoderm explants, a phenomenon known as autoinduction. Acknowledgment of these contributions by Just in no way diminishes the importance of Holtfreter's groundbreaking work. It does, however, extend the impact of Just's work into the area of embryo morphogenesis. It connects Just to Holtfreter and positions his work as an antecedent to embryo research that continues to this day.