Mechanical mechanisms of morphogenesis as potential substrates for evolutionary change.

The first quarter of this century has seen a resurgence of interest in the mechanical and physical mechanisms that drive cellular behaviors in the context of morphogenesis. Far from being a new discovery, the fact that the material properties of cells and the physical forces that they exert and experience must play decisive roles in development, was an important part of the field of experimental embryology well over a century ago. Following the birth of molecular biology, and the development of live imaging approaches that can capture the dynamics of both cellular properties and materials, and the activity of genes and gene products, the current manifestation of this field promises to link mechanical and molecular genetic mechanisms.

Protein sequence evolution underlies interspecies incompatibility of a cell fate determinant.

Novel and rapidly evolving genes can integrate into conserved gene networks and play critical roles in development. Understanding how sequence variation across the orthologs of such genes influences functional interactions with the molecular products of older, more conserved genes requires investigation at the level of protein function. Here, we elucidate how protein-coding sequence evolution in a gene required for primordial germ cell specification and embryonic patterning in fruit flies, has led to functional incompatibility between orthologs from and .

The LOTUS domain of Oskar promotes localisation of both protein and mRNA components of germ plasm.

Germ cells transmit genetic information to the next generation in multicellular organisms. In , germ cells are determined by germ plasm, a specialised cytoplasm assembled by the Oskar protein. The current view of the molecular mechanism of germ plasm assembly attributes recruitment of protein and mRNA germ plasm components to distinct domains of the Oskar protein, called the LOTUS and OSK domains respectively.

Chinmo is a novel regulator of differential Hippo signaling response within a single developing organ.

Orchestrated control of proliferation of multiple cell types is essential for building a healthy organ. Here we use larval ovary development in as a model to understand the homeostasis of somatic and germ line cells in the formation of the female adult reproductive organ. We previously showed that the highly conserved Hippo signaling pathway regulates proliferation of both germ line and somatic cells in the larval ovary.

Duplex PCR assay to determine sex and mating status of Ixodes scapularis (Acari: Ixodidae), vector of the Lyme disease pathogen.

Ticks are a major health threat to humans and other animals, through direct damage, toxicoses, and transmission of pathogens. An estimated half a million people are treated annually in the United States for Lyme disease, a disease caused by the bite of a black-legged tick (Ixodes scapularis Say, 1821) infected with the bacterial pathogen Borrelia burgdorferi. This tick species also transmits another 6 human-disease causing pathogens, for which vaccines are currently unavailable.

Divergence of germ cell-less roles in germ line development across insect species.

During development, sexually reproducing animals must specify and maintain the germ line, the lineage of cells that gives rise to the next generation of animals. In the fruit fly Drosophila melanogaster, germ cell-less (gcl) is required for the formation of primordial germ cells in the form of cells that cellularize at the posterior pole of the embryo, called pole cells. Forming pole cells is a mechanism of germ cell formation unique to a subset of insects.

Establishment of CRISPR/Cas9-based knock-in in a hemimetabolous insect: targeted gene tagging in the cricket Gryllus bimaculatus.

Studies of traditional model organisms such as the fruit fly Drosophila melanogaster have contributed immensely to our understanding of the genetic basis of developmental processes. However, the generalizability of these findings cannot be confirmed without functional genetic analyses in additional organisms. Direct genome editing using targeted nucleases has the potential to transform hitherto poorly understood organisms into viable laboratory organisms for functional genetic study.

Gene Protein Sequence Evolution Can Predict the Rapid Divergence of Ovariole Numbers in the Drosophila melanogaster Subgroup.

Ovaries play key roles in fitness and evolution: they are essential female reproductive structures that develop and house the eggs in sexually reproducing animals. In Drosophila, the mature ovary contains multiple tubular egg-producing structures known as ovarioles. Ovarioles arise from somatic cellular structures in the larval ovary called terminal filaments (TFs), formed by TF cells and subsequently enclosed by sheath (SH) cells.

acts with the transcription factor Creb to regulate long-term memory in crickets.

Novel genes have the potential to drive the evolution of new biological mechanisms, or to integrate into preexisting regulatory circuits and contribute to the regulation of older, conserved biological functions. One such gene, the novel insect-specific gene was first identified based on its role in establishing the germ line. We previously showed that this gene likely arose through an unusual domain transfer event involving bacterial endosymbionts and played a somatic role before evolving its well-known germ line function.

The evolution of ovary-biased gene expression in Hawaiian Drosophila.

With detailed data on gene expression accessible from an increasingly broad array of species, we can test the extent to which our developmental genetic knowledge from model organisms predicts expression patterns and variation across species. But to know when differences in gene expression across species are significant, we first need to know how much evolutionary variation in gene expression we expect to observe. Here we provide an answer by analyzing RNAseq data across twelve species of Hawaiian Drosophilidae flies, focusing on gene expression differences between the ovary and other tissues.

Nuclear speed and cycle length co-vary with local density during syncytial blastoderm formation in a cricket.

The blastoderm is a broadly conserved stage of early animal development, wherein cells form a layer at the embryo's periphery. The cellular behaviors underlying blastoderm formation are varied and poorly understood. In most insects, the pre-blastoderm embryo is a syncytium: nuclei divide and move throughout the shared cytoplasm, ultimately reaching the cortex.

Cricket: The third domesticated insect.

Many researchers are using crickets to conduct research on various topics related to development and regeneration in addition to brain function, behavior, and biological clocks, using advanced functional and perturbational technologies such as genome editing. Recently, crickets have also been attracting attention as a food source for the next generation of humans. In addition, crickets are increasingly being used as disease models and biological factories for pharmaceuticals.

Genomics and genome editing techniques of crickets, an emerging model insect for biology and food science.

Most tools available for manipulating gene function in insects have been developed for holometabolous species. In contrast, functional genetics tools for the Hemimetabola are highly underdeveloped. This is a barrier both to understanding ancestral insect biology, and to optimizing contemporary study and manipulation of particular large hemimetabolous orders of crucial economic and agricultural importance like the Orthoptera.

Phylotranscriptomics Reveals Discordance in the Phylogeny of Hawaiian Drosophila and Scaptomyza (Diptera: Drosophilidae).

Island radiations present natural laboratories for studying the evolutionary process. The Hawaiian Drosophilidae are one such radiation, with nearly 600 described species and substantial morphological and ecological diversification. These species are largely divided into a few major clades, but the relationship between clades remains uncertain.

Distinct gene expression dynamics in germ line and somatic tissue during ovariole morphogenesis in Drosophila melanogaster.

The survival and evolution of a species is a function of the number of offspring it can produce. In insects, the number of eggs that an ovary can produce is a major determinant of reproductive capacity. Insect ovaries are made up of tubular egg-producing subunits called ovarioles, whose number largely determines the number of eggs that can be potentially laid.

Evolution of a Cytoplasmic Determinant: Evidence for the Biochemical Basis of Functional Evolution of the Novel Germ Line Regulator Oskar.

Germ line specification is essential in sexually reproducing organisms. Despite their critical role, the evolutionary history of the genes that specify animal germ cells is heterogeneous and dynamic. In many insects, the gene oskar is required for the specification of the germ line.

Insights into the genomic evolution of insects from cricket genomes.

Most of our knowledge of insect genomes comes from Holometabolous species, which undergo complete metamorphosis and have genomes typically under 2 Gb with little signs of DNA methylation. In contrast, Hemimetabolous insects undergo the presumed ancestral process of incomplete metamorphosis, and have larger genomes with high levels of DNA methylation. Hemimetabolous species from the Orthopteran order (grasshoppers and crickets) have some of the largest known insect genomes.

Evolutionary dynamics of sex-biased genes expressed in cricket brains and gonads.

Sex-biased gene expression, particularly sex-biased expression in the gonad, has been linked to rates of protein sequence evolution (nonsynonymous to synonymous substitutions, dN/dS) in animals. However, in insects, sex-biased expression studies remain centred on a few holometabolous species. Moreover, other major tissue types such as the brain remain underexplored.

Repeated loss of variation in insect ovary morphology highlights the role of development in life-history evolution.

The number of offspring an organism can produce is a key component of its evolutionary fitness and life history. Here we perform a test of the hypothesized trade-off between the number and size of offspring using thousands of descriptions of the number of egg-producing compartments in the insect ovary (ovarioles), a common proxy for potential offspring number in insects. We find evidence of a negative relationship between egg size and ovariole number when accounting for adult body size.

Adaptation of codon and amino acid use for translational functions in highly expressed cricket genes.

Background: For multicellular organisms, much remains unknown about the dynamics of synonymous codon and amino acid use in highly expressed genes, including whether their use varies with expression in different tissue types and sexes. Moreover, specific codons and amino acids may have translational functions in highly transcribed genes, that largely depend on their relationships to tRNA gene copies in the genome. However, these relationships and putative functions are poorly understood, particularly in multicellular systems.

Topology-driven protein-protein interaction network analysis detects genetic sub-networks regulating reproductive capacity.

Understanding the genetic regulation of organ structure is a fundamental problem in developmental biology. Here, we use egg-producing structures of insect ovaries, called ovarioles, to deduce systems-level gene regulatory relationships from quantitative functional genetic analysis. We previously showed that Hippo signalling, a conserved regulator of animal organ size, regulates ovariole number in .

Null hypotheses for developmental evolution.

How much evolutionary change in development do we expect? In this Spotlight, we argue that, as developmental biologists, we are in a prime position to contribute to the definition of a null hypothesis for developmental evolution: in other words, a hypothesis for how much developmental evolution we expect to observe over time. Today, we have access to an unprecedented array of developmental data from across the tree of life. Using these data, we can now consider development in the light of evolution, and vice versa, more deeply than ever before.