Brachyury controls Ciona notochord fate as part of a feed-forward network.

The notochord is a defining feature of the chordates. The transcription factor Brachyury (Bra) is a key regulator of notochord fate but here we show that it is not a unitary master regulator in the model chordate Ciona Ectopic Bra expression only partially reprograms other cell types to a notochord-like transcriptional profile and a subset of notochord-enriched genes is unaffected by CRISPR Bra disruption. We identify Foxa.a and Mnx as potential co-regulators, and find that combinatorial cocktails are more effective at reprogramming other cell types than Bra alone. We reassess the network relationships between Bra, Foxa.a and other components of the notochord gene regulatory network, and find that Foxa.a expression in the notochord is regulated by vegetal FGF signaling. It is a direct activator of Bra expression and has a binding motif that is significantly enriched in the regulatory regions of notochord-enriched genes. These and other results indicate that Bra and Foxa.a act together in a regulatory network dominated by positive feed-forward interactions, with neither being a classically defined master regulator.

Single-cell analysis of cell fate bifurcation in the chordate Ciona.

BACKGROUND: Inductive signaling interactions between different cell types are a major mechanism for the further diversification of embryonic cell fates. Most blastomeres in the model chordate Ciona robusta become restricted to a single predominant fate between the 64-cell and mid-gastrula stages. The deeply stereotyped and well-characterized Ciona embryonic cell lineages allow the transcriptomic analysis of newly established cell types very early in their divergence from sibling cell states without the pseudotime inference needed in the analysis of less synchronized cell populations. This is the first ascidian study to use droplet scRNAseq with large numbers of analyzed cells as early as the 64-cell stage when major lineages such as primary notochord first become fate restricted. RESULTS AND CONCLUSIONS: We identify 59 distinct cell states, including new subregions of the b-line neural lineage and the early induction of the tail tip epidermis. We find that 34 of these cell states are directly or indirectly dependent on MAPK-mediated signaling critical to early Ciona patterning. Most of the MAPK-dependent bifurcations are canalized with the signal-induced cell fate lost upon MAPK inhibition, but the posterior endoderm is unique in being transformed into a novel state expressing some but not all markers of both endoderm and muscle. Divergent gene expression between newly bifurcated sibling cell types is dominated by upregulation in the induced cell type. The Ets family transcription factor Elk1/3/4 is uniquely upregulated in nearly all the putatively direct inductions. Elk1/3/4 upregulation together with Ets transcription factor binding site enrichment analysis enables inferences about which bifurcations are directly versus indirectly controlled by MAPK signaling. We examine notochord induction in detail and find that the transition between a Zic/Ets-mediated regulatory state and a Brachyury/FoxA-mediated regulatory state is unexpectedly late. This supports a "broad-hourglass" model of cell fate specification in which many early tissue-specific genes are induced in parallel to key tissue-specific transcriptional regulators via the same set of transcriptional inputs.

Development of a Fission Neutron Spectrum from a D-T Neutron Generator by Spectrum Subtraction Technique.

ABSTRACT: Californium-252 (252Cf) is considered essential by the National Institute of Standards and Technology for the calibration of neutron instrumentation and dosimetry. Californium-252 has a relatively short half-life of 2.645 y; consequently, it must be replaced frequently to produce an adequate neutron flux for calibration. The user community is currently looking for a replacement for 252Cf. The patented technology described herein has a high probability of being that replacement. A preferred method to replace 252Cf would use an affordable and easily maintained neutron source that generates neutrons in an energy spectrum as close to that of 252Cf as possible. Deuterium-tritium (D-T) neutron generators are both affordable and easily maintained, which makes them highly attractive for replacing 252Cf. The patented technology discussed in this paper simulates the 252Cf fission spectrum through a D-T neutron generator by using spectral subtraction. The primary spectrum is built using principally (n,xn) and (n,n') reactions in a variety of materials. In conjunction with the primary spectrum, an engineered background spectrum is generated using a second set of materials. This engineered background spectrum corrects for differences between the primary and desired spectra. This subtraction technique generates a spectrum very similar to 252Cf while maintaining a reasonable flux. Further, by choosing different scattering materials, any fission spectrum can be matched, including the thermal and epithermal components. This flexibility expands the potential use of this technology beyond simulating 252Cf to any desired neutron spectrum below 14 MeV.

Tunicate gastrulation.

Tunicates are a diverse group of invertebrate marine chordates that includes the larvaceans, thaliaceans, and ascidians. Because of their unique evolutionary position as the sister group of the vertebrates, tunicates are invaluable as a comparative model and hold the promise of revealing both conserved and derived features of chordate gastrulation. Descriptive studies in a broad range of tunicates have revealed several important unifying traits that make them unique among the chordates, including invariant cell lineages through gastrula stages and an overall morphological simplicity. Gastrulation has only been studied in detail in ascidians such as Ciona and Phallusia, where it involves a simple cup-shaped gastrula driven primarily by endoderm invagination. This appears to differ significantly from vertebrate models, such as Xenopus, in which mesoderm convergent extension and epidermal epiboly are major contributors to involution. These differences may reflect the cellular simplicity of the ascidian embryo.

Nursing frequency, gonadal function, and birth spacing among !Kung hunter-gatherers.

Mothers among !Kung hunter-gatherers nurse briefly and frequently, with brief intervals between nursing bouts (mean +/- standard error, 13.19 +/- 1.28 minutes). The low levels of 17 beta-estradiol and progesterone in the serum of the mother are correlated with infant's age and with interbout interval, but not with total nursing time. Maternal gonadal function is apparently suppressed by a timing-dependent, prolactin-mediated effect of breast stimulation. Interbout interval may be a key variable in lactation infertility. If so, it solves the puzzle of !Kung birth spacing.

Stone agers in the fast lane: chronic degenerative diseases in evolutionary perspective.

From a genetic standpoint, humans living today are Stone Age hunter-gatherers displaced through time to a world that differs from that for which our genetic constitution was selected. Unlike evolutionary maladaptation, our current discordance has little effect on reproductive success; rather it acts as a potent promoter of chronic illnesses: atherosclerosis, essential hypertension, many cancers, diabetes mellitus, and obesity among others. These diseases are the results of interaction between genetically controlled biochemical processes and a myriad of biocultural influences--lifestyle factors--that include nutrition, exercise, and exposure to noxious substances. Although our genes have hardly changed, our culture has been transformed almost beyond recognition during the past 10,000 years, especially since the Industrial Revolution. There is increasing evidence that the resulting mismatch fosters "diseases of civilization" that together cause 75 percent of all deaths in Western nations, but that are rare among persons whose lifeways reflect those of our preagricultural ancestors.

Testosterone levels change with subsistence hunting effort in !Kung San men.

Although little is known empirically of the physiology of human hunting, arguments for innate biological bases of gender-dimorphic behaviors such as aggression frequently point to the role of hunting in human evolution. Study of !Kung San hunter-gatherer men demonstrated that the diurnal pattern in serum testosterone was altered during a six-day hunt, compared to pre- and post-hunt levels, due mainly to elevation of evening values. Hunting success did not correlate with any testosterone measures. The pattern of changes observed is most consistent with the known concomitants of moderate prolonged exercise.

An anthropological perspective on obesity.

An anthropological perspective on obesity considers both its evolutionary background and cross-cultural variation. It must explain three basic facts about obesity: gender dimorphism (women greater than men), an increase with modernization, and a positive association with socioeconomic status. Preindustrial diets varied in quality but shared a tendency to periodic shortages. Such shortages, particularly disadvantageous to women in their reproductive years, favored individuals who, for biological and cultural reasons, stored fat. Not surprisingly, the majority of the world's cultures had or have ideals of feminine beauty that include plumpness. This is consistent with the hypothesis that fat stores functioned as a cushion against food shortages during pregnancy and lactation. As obesity has increased, the traditional gap between males and females in its prevalence has narrowed. Under Western conditions of abundance, our biological tendency to regulate body weight at levels above our ideal cannot be easily controlled even with a complete reversal of the widespread cultural ideal of plumpness.

Nursing frequency and birth spacing in Kung hunter-gatherers.

PIP: In a study on infant growth and development among the ]Kung San, hunter-gatherers of northwestern Botswana in 1969-71, a pattern of nursing was observed that was striking. Age at weaning was typically later than 3 years; all infants under a year of age in the population were nursing, as were 90% of those in the second year, and 75% of those in the third year. Child under 3 awoke to nurse 1 or more times in the night. Nursing in the day was frequent and brief. At all ages under 2 years, fewer than 25% of 15 minute observations of the mother-infant pair elapsed without a nursing session. The ]Kung population has unusually long birth spacing, as high as 44 months in traditional bands, resulting in an overall low natural fertility of 4.7 live births per woman. Extensive experimental and clinical literature shows that prolactin is promptly secreted in response to nipple stimulation in human females, increasing 2 to 20 fold in plasma during 5 to 15 minutes of mechanical stimulation, with a half-life in plasma of 10 to 30 minutes. Prolactin suppresses gonadal function, either directly at the ovary or indirectly through gonadotropin antagonism at the anterior pituitary. When the child is between 2 and 3 years old, the level of prolactin, which presumably had been tonically high previously, is allowed to fall low enough for a long enough time so that its antigonadal or antigonadotrophic effects are impaired, and ovarian cycling is reinstated.^ieng

Stone age nutrition: implications for today.

The nutritional elements appropriate for contemporary humans reflect genetically determined biochemical and physiological factors, which have evolved over hundreds of millions of years. Stone Age humans, however, derived nearly all of their nutrients from just two of the four major food groups we select from today.

Crying in !Kung San infants: a test of the cultural specificity hypothesis.

The pattern of crying and fretting behavior during the first two years is described for 46 !Kung San infants from a hunter-gatherer society in northwestern Botswana. Despite markedly different caretaking practices predisposing to quieter infants, crying and fretting were significantly greater during the first three months, and a peak pattern was present. Measurement of crying 'intensity' indicated that it was predominantly short and fretful. The results support the concept that the early peak pattern is not specific to infants in western industrialized societies, and may represent a behavior universal to the human species. The caretaking differences between societies primarily appear to affect crying duration rather than its frequency and pattern in early infancy.

Kung infancy: the social context of object exploration.

The present study consists of new analyses of systematic observations of Kung infants made by Konner during the late 1960s and early 1970s. Our intent was to examine claims about the role of object sharing in development by describing how Kung infants develop interest in objects and how their caregivers act toward them when they are engaged in object-related acts. Results indicated that infants first displayed sustained interest in objects beginning at 4 months of age and that, beginning at about 8 months, they also began to engage in relational play and to give objects to others. Others tended to ignore infants during episodes of object manipulation and play, but moments of object offering were often socially embedded. These findings provide support for claims that there are universal changes in infants' involvement with objects and that their involvement is channeled in a culturally relevant manner by their caregivers.

Nursing behaviour, prolactin and postpartum amenorrhoea during prolonged lactation in American and !Kung mothers.

In order to determine the effects of protracted nursing in American women, blood was collected hourly for 24 h and nursing periods recorded in 20 mothers, 10 amenorrhoeic, 3 3/4 to 17 1/4 months postpartum (PP), and 10 menstruating, 5 1/4 to 46 months PP. These data were compared to the daytime nursing behaviour and 1000-1100 h PRL of women among !Kung hunter-gatherers of Botswana, a non-contraceptive using population with a birth space interval of greater than 3 years. Intense nursing behaviour maintained amenorrhoea and hyperprolactinaemia for 1 to nearly 2 years PP in both American and !Kung mothers. Among Americans, 80 min of nursing per day, in conjunction with a minimum of six nursing episodes, was highly predictive of remaining amenorrhoeic up to 18 months PP. Amenorrhoea was always accompanied by hyperprolactinaemia, but delay in the onset of menses was related more to nursing behaviour than to a particular 24 h PRL level. The 1000-1100 h sample is equivalent to and about half of the 24 h mean in high and low intensity nursers, respectively. The !Kung women were similar to the high intensity nursing American women in 1000-1100 h PRL, percent amenorrhoeic, and the number of minutes of daytime nursing.