ERK1/2 is an ancestral organising signal in spiral cleavage

Animal development is classified as conditional or autonomous based on whether cell fates are specified through inductive signals or maternal determinants, respectively. Yet how these two major developmental modes evolved remains unclear. During spiral cleavage—a stereotypic embryogenesis ancestral to 15 invertebrate groups, including molluscs and annelids—most lineages specify cell fates conditionally, while some define the primary axial fates autonomously. To identify the mechanisms driving this change, we studied Owenia fusiformis, an early-branching, conditional cleaving annelid. In Owenia, ERK1/2-mediated FGF receptor signalling specifies the endomesodermal progenitor. This cell acts as an embryonic organiser, inducing mesodermal and posterodorsal fates in neighbouring cells and repressing anteriorising signals. The organising role of ERK1/2 in Owenia is shared with molluscs, but not with autonomous cleaving annelids. Together, these findings indicate that conditional specification of an ERK1/2+ organiser is ancestral in spiral cleavage, repeatedly lost in annelid lineages as they evolved autonomous development.

Maternal Determinants Mediating the Impact of Household Poverty on the Nutritional Status of Children Under 5 Years of Age in Bangladesh

Objectives: We explored the maternal determinants that mediate the effect of household poverty on childhood undernutrition. Methods: We used the population-based Bangladesh Demographic Health Survey data from 2014 for demographic characteristics, child and maternal factors. Results: Of the 7173 under-5 children, 3456 (48.2%) had undernutrition. The prevalence of undernutrition was less common in wealthy households (poorest vs richest: adjusted prevalence ratio [aPR] = 1.37), mothers having history of antenatal care (ANC) visits (no visit vs ≥4 visits: aPR = 1.22), maternal higher education (no education vs higher education: aPR = 1.54), and mothers with good nutritional status (underweight vs healthy: aPR = 1.13). The risk of undernutrition (37.1%) was attributed to household wealth, mediated 55% by maternal factors; of which 20% by maternal education, 21% by ANC visits, and 14% by maternal nutritional status. Conclusions: Our study findings outlined higher maternal education, ≥4 ANC visits and maternal good nutritional status in mediating the impact of household wealth on childhood nutrition.

Pescoids and Chimeras to Probe Early Evo-Devo in the Fish Astyanax mexicanus

The fish species Astyanax mexicanus with its sighted and blind eco-morphotypes has become an original model to challenge vertebrate developmental evolution. Recently, we demonstrated that phenotypic evolution can be impacted by early developmental events starting from the production of oocytes in the fish ovaries. A. mexicanus offers an amenable model to test the influence of maternal determinants on cell fate decisions during early development, yet the mechanisms by which the information contained in the eggs is translated into specific developmental programs remain obscure due to the lack of specific tools in this emergent model. Here we describe methods for the generation of pescoids from yolkless-blastoderm explants to test the influence of embryonic and extraembryonic tissues on cell fate decisions, as well as the production of chimeric embryos obtained by intermorph cell transplantations to probe cell autonomous or non-autonomous processes. We show that Astyanax pescoids have the potential to recapitulate the main ontogenetic events observed in intact embryos, including the internalization of mesodermal progenitors and eye development, as followed with zic:GFP reporter lines. In addition, intermorph cell grafts resulted in proper integration of exogenous cells into the embryonic tissues, with lineages becoming more restricted from mid-blastula to gastrula. The implementation of these approaches in A. mexicanus will bring new light on the cascades of events, from the maternal pre-patterning of the early embryo to the evolution of brain regionalization.

Dynamic organization of cortical actin filaments during the ooplasmic segregation of ascidian Ciona eggs

Spatial reorganization of cytoplasm in zygotic cells is critically important for establishing the body plans of many animal species. In ascidian zygotes, maternal determinants (mRNAs) are first transported to the vegetal pole a few minutes after the fertilization, and then to the future posterior side of the zygotes in later phase of the cytoplasmic reorganization, before the first cell division. Here, by using a novel fluorescence polarization microscope that reports the position and the orientation of fluorescently labeled proteins in living cells, we mapped the local alignments and the time-dependent changes of cortical actin networks in Ciona eggs. The initial cytoplasmic reorganization started with the contraction of vegetal hemisphere approximately 20 s after the fertilization induced [Ca2+] increase. Timing of the vegetal contraction was consistent with the emergence of highly aligned actin filaments at the cell cortex of vegetal hemisphere which ran perpendicular to the animal-vegetal axis. We propose that the cytoplasmic reorganization is initiated by the local contraction of laterally aligned cortical actomyosin in the vegetal hemisphere, which in turn generates the directional movement of cytoplasm within whole egg. [Media: see text] [Media: see text] [Media: see text] [Media: see text] [Media: see text] [Media: see text] [Media: see text] [Media: see text]