Dynamics of maternal gene expression in Rhodnius prolixus

The study of the developmental processes in Rhodnius prolixus has recently advanced with the sequencing of the genome. In this work, we study maternal gene expression driving oogenesis and early embryogenesis in R. prolixus. We analyze the transcriptional profile of mRNAs to establish the genes expressed across the ovary, unfertilized eggs and different embryonic stages of R. prolixus until the formation of the germ band anlage (0, 12, 24, and 48 hours post egg laying). We identified 81 putative maternal and ovary-related genes and validated their expression by qRT-PCR. Consistent with a role in oogenesis and early development of R. prolixus, we show that parental RNAi against Rp-BicD results in embryos that did not show any distinguishable embryonic structure. In this framework we propose three hierarchies of maternal genes that affect early and late oogenesis, and embryonic patterning.

Instrumentalizing and Visualizing the Cosmic First Light

What material and visual means have astrophysicists and cosmologists developed to explain the composition and history of our universe? The emergence of high-precision, big-data, born-digital cosmology in the late-20th century depended upon detecting, interrogating, and making visible the universe’s very first light—the cosmic microwave background (CMB) radiation. This article analyses how, between 1974 and 2013, physicists and space scientists grappled with building interlinked instruments that could engage with the material effects of light to visualize, map, and interpret these invisible primordial messages. Astrophysicists, instrument-builders, and engineers used data collected from instruments on NASA’s COBE and WMAP and ESA’s Planck space probes to produce iconic images mapping the universe’s embryonic structure, theoretically-anchored precision visualizations modeling the evolution of cosmic structure from the big bang to today. This paper argues that creative aesthetic concerns appeared at all stages in these missions, from instrument design to image production to public outreach.

Brassinosteroids repress the seed maturation program during the seed-to-seedling transition

In flowering plants, repression of the seed maturation program is essential for the transition from the seed to the vegetative phase, but the underlying mechanisms remain poorly understood. The B3-domain protein VIVIPAROUS1/ABSCISIC ACID-INSENSITIVE3-LIKE 1 (VAL1) is involved in repressing the seed maturation program. Here we uncovered a molecular network triggered by the plant hormone brassinosteroid (BR) that inhibits the seed maturation program during the seed-to-seedling transition in Arabidopsis (Arabidopsis thaliana). val1-2 mutant seedlings treated with a BR biosynthesis inhibitor form embryonic structures, whereas BR signaling gain-of-function mutations rescue the embryonic structure trait. Furthermore, the BR-activated transcription factors BRI1-EMS-SUPPRESSOR 1 and BRASSINAZOLE-RESISTANT 1 bind directly to the promoter of AGAMOUS-LIKE15 (AGL15), which encodes a transcription factor involved in activating the seed maturation program, and suppress its expression. Genetic analysis indicated that BR signaling is epistatic to AGL15 and represses the seed maturation program by downregulating AGL15. Finally, we showed that the BR-mediated pathway functions synergistically with the VAL1/2-mediated pathway to ensure the full repression of the seed maturation program. Together, our work uncovered a mechanism underlying the suppression of the seed maturation program, shedding light on how BR promotes seedling growth.

Quail-chick grafting experiments corroborate that Tbr1-positive eminential prethalamic neurons migrate along three streams into hypothalamus, subpallium and septocommissural areas

The prethalamic eminence (PThE), a diencephalic caudal neighbor of the telencephalon and alar hypothalamus, is frequently described in mammals and birds as a transient embryonic structure, undetectable in the adult brain. Based on descriptive developmental analysis of Tbr1 gene brain expression in chick embryos, we previously reported that three migratory cellular streams exit the PThE rostralward, targeting multiple sites in the hypothalamus, subpallium and septocommissural area, where eminential cells form distinct nuclei or disperse populations. These conclusions needed experimental corroboration. In this work, we used the homotopic quail-chick chimeric grafting procedure at stages HH10/HH11 to demonstrate by fate-mapping the three predicted tangential migration streams. Some chimeric brains were processed for Tbr1 in situ hybridization, for correlation with our previous approach. Evidence supporting all three postulated migration streams is presented. The results suggested a slight heterochrony among the juxtapeduncular (first), the peripeduncular (next), and the eminentio-septal (last) streams, each of which followed differential routes. A possible effect of such heterochrony on the differential selection of medial to lateral habenular hodologic targets by the migrated neurons is discussed.

Development of Embryo Suspensors for Five Genera of Crassulaceae with Special Emphasis on Plasmodesmata Distribution and Ultrastructure

The suspensor in the majority of angiosperms is an evolutionally conserved embryonic structure functioning as a conduit that connects ovule tissues with the embryo proper for nutrients and growth factors flux. This is the first study serving the purpose of investigating the correlation between suspensor types and plasmodesmata (PD), by the ultrastructure of this organ in respect of its full development. The special attention is paid to PD in representatives of Crassulaceae genera: Sedum, Aeonium, Monanthes, Aichryson and Echeveria. The contribution of the suspensor in transporting nutrients to the embryo was confirmed by the basal cell structure of the suspensor which produced, on the micropylar side of all genera investigated, a branched haustorium protruding into the surrounding ovular tissue and with wall ingrowths typically associated with cell transfer. The cytoplasm of the basal cell was rich in endoplasmic reticulum, mitochondria, dictyosomes, specialized plastids, microtubules, microbodies and lipid droplets. The basal cell sustained a symplasmic connection with endosperm and neighboring suspensor cells. Our results indicated the dependence of PD ultrastructure on the type of suspensor development: (i) simple PD are assigned to an uniseriate filamentous suspensor and (ii) PD with an electron-dense material are formed in a multiseriate suspensor. The occurrence of only one or both types of PD seems to be specific for the species but not for the genus. Indeed, in the two tested species of Sedum (with the distinct uniseriate/multiseriate suspensors), a diversity in the structure of PD depends on the developmental pattern of the suspensor. In all other genera (with the multiseriate type of development of the suspensor), the one type of electron-dense PD was observed.

Building Principles for Constructing a Mammalian Blastocyst Embryo

The self-organisation of a fertilised egg into an embryo of three distinct cell lineages (trophoblast, epiblast and hypoblast) arranged around an off-centre cavity typifies the blastocyst, an embryonic structure that is unique to mammals. While the starting point (the zygote) and endpoint (the blastocyst) are similar in all mammals, the intervening events have diverged. This review examines and compares the descriptive and functional data surrounding embryonic gene activation, symmetry-breaking, first and second lineage establishment and fate commitment in a wide range of mammalian orders. The exquisite detail known from mouse embryogenesis, embryonic stem cell studies and the wealth of recent single cell transcriptomic experiments are used to highlight the building principles underlying early mammalian embryonic development.

Neurobiology of Monotremes

Neurobiology of Monotremes brings together current information on the development, structure, function and behavioural ecology of the monotremes. The monotremes are an unusual and evolutionarily important group of mammals showing striking behavioural and physiological adaptations to their niches. They are the only mammals exhibiting electroreception (in the trigeminal sensory pathways) and the echidna shows distinctive olfactory specialisations. The authors aim to close the current gap in knowledge between the genes and developmental biology of monotremes on the one hand, and the adult structure, function and ecology of monotremes on the other. They explore how the sequence 'embryonic structure › adult structure › behaviour' is achieved in monotremes and how this differs from other mammals. The work also combines a detailed review of the neurobiology of monotremes with photographic and diagrammatic atlases of the sectioned adult brains and peripheral nervous system of the short-beaked echidna and platypus. Pairing of a detailed review of the field with the first published brain atlases of two of the three living monotremes will allow the reader to immediately relate key points in the text to features in the atlases and will extend a universal system of brain nomenclature developed in eutherian brain atlases by G Paxinos and colleagues to monotremes.