Multiple feedback loops through cytokinin signaling control stem cell number within the Arabidopsis shoot meristem

A central unanswered question in stem cell biology, both in plants and in animals, is how the spatial organization of stem cell niches are maintained as cells move through them. We address this question for the shoot apical meristem (SAM) which harbors pluripotent stem cells responsible for growth of above-ground tissues in flowering plants. We find that localized perception of the plant hormone cytokinin establishes a spatial domain in which cell fate is respecified through induction of the master regulator WUSCHEL as cells are displaced during growth. Cytokinin-induced WUSCHEL expression occurs through both CLAVATA-dependent and CLAVATA-independent pathways. Computational analysis shows that feedback between cytokinin response and genetic regulators predicts their relative patterning, which we confirm experimentally. Our results also may explain how increasing cytokinin concentration leads to the first steps in reestablishing the shoot stem cell niche in vitro

Milk digestion in the young rabbit: methodology and first results

[EN] This study aims to determine the digestibility of milk by the young rabbit (21-25 d old), taking into account the increment of digesta content and urine excretion. Nineteen litters of 9 young rabbits 21 to 25 d old were used: 12 litters (S group) fed exclusively with milk using controlled suckling, and 7 litters (Control group) with free suckling and access to the pelleted feed of the doe. The faecal digestibility of milk dry matter (DM) was measured between 21 and 25 d of age, for S litters housed from 15 d of age in a metabolism cage separately from their mother. Between 21 and 25 d, the milk intake, faeces and urine excretion were controlled daily, and the mean increment in digesta content was measured by comparing digesta weight of the whole tract at 21 and 25 d of age (one kit per litter). The increment in digesta content from 21 to 25 d averaged 77% (+8.5 g), sourcing mainly from stomach and caecum contents increase (+57 and +120% respectively). The mean increase for the dry content of the gut (from 21 to 25 d) was 1.75 g DM/kit, and was considered as non-digested to calculate the digestibility coefficient of the milk. The milk intake averaged 30 g/d/kit (7.9 g DM/d kit). No faecal excretion was recorded between 21 and 25 d. From the milk intake and increment in digesta content, the corrected digestibility of the milk dry matter reached 94% (minimum=92.9%, maximum=95.6%). The daily urine excretion averaged 5.1 mL/kit, corresponding to 1.2 g DM/kit. Therefore, the corrected DM retention coefficient of the milk was 79.5%. The quantity of nitrogen excreted in urine was low (0.06 g/d kits), thus the corrected nitrogen retention coefficient for milk reached 82% and the nitrogen retained (corrected) reached 0.44 g/d kit. Accordingly, the amount in metabolisable protein for the milk was 90 g/kg (fresh). The corrected energy retention coefficient was estimated to 95.8%, for a crude energy concentration estimated at 28.14 MJ/kg DM for the milk. Thus, the energy retained (corrected) reached 223 kJ/d kit and the content in metabolisable energy for the milk was 26.94 MJ/kg DM.The authors thank INRA PHASE division for the financial support. The authors would also like to thank the technicians involved in the experiment at the INRA UE PECTOUL (Patrick Aymard, Jacques De Dapper & Jean De Dapper) and in the GenPhySE laboratory (Véronique Tartié).Gidenne, TN.; Bannelier, C.; Gallois, M.; Segura, M.; Lambrecht, V. (2018). Milk digestion in the young rabbit: methodology and first results. World Rabbit Science. 26(4):269-276. doi:10.4995/wrs.2018.10061SWORD269276264Alstin F., Nilsson M. 1990. The Soxtec®hydrolysis system improves the official methods for determining total fat content. Ind. Alim. Agric., 107: 1271-1274.Carabaño R., Piquer J., Menoyo D., Badiola I. 2010. The digestive system of the rabbit, In: De Blas C., Wiseman J. (Eds.), Nutrition of the rabbit, CABI; Wallingford; UK, pp. 1-18. https://doi.org/10.1079/9781845936693.0001EGRAN. 2001. Technical note: Attempts to harmonise chemical analyses of feeds and faeces, for rabbit feed evaluation. World Rabbit Sci., 9: 57-64. https://doi.org/10.4995/wrs.2001.446Gallois M., Gidenne T., Fortun-Lamote F., Le Hueron-Luron I., Lallès J.P. 2005. An early stimulation of solid feed intake slightly influences the morphological gut maturation in the rabbit. Reprod. Nutr. Develop., 45: 109-122. https://doi.org/10.1017/S1751731108001730Gallois M., Fortun-Lamothe L., Michelan A., Gidenne T. 2008. Adaptability of the digestive function according to age at weaning in the rabbit: II. Effect on nutrient digestion in the small intestine and in the whole digestive tract. Animal, 2: 536-547. https://doi.org/10.1017/S1751731108001730Gidenne T., Debray L., Fortun-Lamothe L., Le Huerou-Luron I. 2007. Maturation of the intestinal digestion and of microbial activity in the young rabbit: Impact of the dietary fibre:starch ratio. Comp. Bioch. Physiol. - Part A: Molecular & Integrative Physiology, 148: 834-844. https://doi.org/10.1016/j.cbpa.2007.08.025Gidenne T., Lebas F., Savietto D., Dorchies P., Duperray J., Davoust C., Fortun-Lamothe L. 2015. Nutrition et alimentation, In: Gidenne T. (Ed.), Le lapin. De la biologie à l'élevage, Quae éditions, pp. 152-196.Lebas, F. 1971. Composition chimique du lait de lapine évolution au cours de la traite et en fonction du stade de lactation. Ann. Zootech., 20: 185-191. https://doi.org/10.1051/animres:19710205Maertens L., Lebas F., Szendrő Zs. 2006. Rabbit milk: a review of quantity, quality and non-dietary affecting factors. World Rabbit Sci., 14: 205-203. https://doi.org/10.4995/wrs.2006.565Orengo J., Gidenne T. 2007. Feeding behaviour and caecotrophy in the young rabbit before weaning: An approach by analysing the digestive contents. App. Anim. Behav. Sci., 102: 106-118. https://doi.org/10.1016/j.applanim.2006.03.010Parigi Bini R., Cesselli P. 1976. Estimate of energy excreted in urine by growing rabbits. In: 1st World Rabbit Congress, Dijon, France, Comm. 20, 6.Parigi Bini R., Xiccato G., Cinetto M., Dalle Zotte A. 1991. Digestive efficiency and energy and protein retention in suckling and weanling rabbits. Zootec. Nutr. Anim., 17: 167-180.Savietto D., Cervera C., Blas E., Baselga M., Larsen T., Friggens N.C., Pascual J.J. 2014. Environmental sensitivity differs between rabbit lines selected for reproductive intensity and longevity. Animal, 7: 1969-1977. https://doi.org/10.1017/S175173111300178XUbilla E., Rebollar P.G., Pazo D., Esquifino A., Alvariño J.M.R. 2000. Effects of doe-litter separation on endocrinological and productivity variables in lactating rabbits. Livest. Prod. Sci., 67: 67-74. https://doi.org/10.1016/S0301-6226(00)00196-2Udert K.M., Larsen T.A., Biebow M., Gujer W.P. 2003. Urea hydrolysis and precipitation dynamics in a urinecollecting system. Water Res., 37: 2571-2582. https://doi.org/10.1016/S0043-1354(03)00065-4Zhang Y.K., Cui H.X., Sun D.F., Liu L.H., Xu X.R. 2018. Effects of doe-litter separation on intestinal bacteria, immune response and morphology of suckling rabbits. World Rabbit Sci., 26: 71-79. https://doi.org/10.4995/wrs.2018.591

Fatty liver and insulin resistance in obese Zucker rats: No role for mitochondrial dysfunction

The relationship between insulin resistance and mitochondrial function is of increasing interest. Studies looking for such interactions are usually made in muscle and only a few studies have been done in liver, which is known to be a crucial partner in whole body insulin action. Recent studies have revealed a similar mechanism to that of muscle for fat-induced insulin resistance in liver. However, the exact mechanism of lipid metabolites accumulation in liver leading to insulin resistance is far from being elucidated. One of the hypothetical mechanisms for liver steatosis development is an impairment of mitochondrial function. We examined mitochondrial function in fatty liver and insulin resistance state using isolated mitochondria from obese Zucker rats. We determined the relationship between ATP synthesis and oxygen consumption as well as the relationship between mitochondrial membrane potential and oxygen consumption. In order to evaluate the quantity of mitochondria and the oxidative capacity we measured citrate synthase and cytochrome c oxidase activities. Results showed that despite significant fatty liver and hyperinsulinemia, isolated liver mitochondria from obese Zucker rats display no difference in oxygen consumption, ATP synthesis, and membrane potential compared with lean Zucker rats. There was no difference in citrate synthase and cytochrome c oxidase activities between obese and lean Zucker rats in isolated mitochondria as well as in liver homogenate, indicating a similar relative amount of hepatic mitochondria and a similar oxidative capacity. Adiponectin, which is involved in bioenergetic homeostasis, was increased two-fold in obese Zucker rats despite insulin resistance. In conclusion, isolated liver mitochondria from lean and obese insulin-resistant Zucker rats showed strictly the same mitochondrial function. It remains to be elucidated whether adiponectin increase is involved in these results

An in vivo root hair assay for determining rates of apoptotic-like programmed cell death in plants

In Arabidopsis thaliana we demonstrate that dying root hairs provide an easy and rapid in vivo model for the morphological identification of apoptotic-like programmed cell death (AL-PCD) in plants. The model described here is transferable between species, can be used to investigate rates of AL-PCD in response to various treatments and to identify modulation of AL-PCD rates in mutant/transgenic plant lines facilitating rapid screening of mutant populations in order to identify genes involved in AL-PCD regulation

The food contaminant fumonisin B1 reduces the maturation of porcine CD11R1+ intestinal antigen presenting cells and antigen-specific immune responses, leading to a prolonged intestinal ETEC infection

Consumption of food or feed contaminated with fumonisin B1 (FB1), a mycotoxin produced by Fusarium verticillioides, can lead to disease in humans and animals. The present study was conducted to examine the effect of FB1 intake on the intestinal immune system. Piglets were used as a target and as a model species for humans since their gastro-intestinal tract is very similar. The animals were orally exposed to a low dose of FB1 (1 mg/kg body weight FB1) for 10 days which did not result in clinical signs. However, when compared to non-exposed animals, FB1-exposed animals showed a longer shedding of F4+ enterotoxigenic Escherichia coli (ETEC) following infection and a lower induction of the antigen-specific immune response following oral immunization. Further analyses to elucidate the mechanisms behind these observations revealed a reduced intestinal expression of IL-12p40, an impaired function of intestinal antigen presenting cells (APC), with decreased upregulation of Major Histocompatibility Complex Class II molecule (MHC-II) and reduced T cell stimulatory capacity upon stimulation. Taken together, these results indicate an FB1-mediated reduction of in vivo APC maturation

Charge gap in the one--dimensional dimerized Hubbard model at quarter-filling

We propose a quantitative estimate of the charge gap that opens in the one-dimensional dimerized Hubbard model at quarter-filling due to dimerization, which makes the system effectively half--filled, and to repulsion, which induces umklapp scattering processes. Our estimate is expected to be valid for any value of the repulsion and of the parameter describing the dimerization. It is based on analytical results obtained in various limits (weak coupling, strong coupling, large dimerization) and on numerical results obtained by exact diagonalization of small clusters. We consider two models of dimerization: alternating hopping integrals and alternating on--site energies. The former should be appropriate for the Bechgaard salts, the latter for compounds where the stacks are made of alternating $TMTSF$ and $TMTTF$ molecules. % $(TMTSF)_2 X$ and $(TMTTF)_2 X$ ($X$ denotes $ClO_4$, $PF_6$, $Br$...).Comment: 33 pages, RevTeX 3.0, figures on reques

Effect of different weaning age (21, 28 or 35 days) on production, growth and certain parameters of the digestive tract in rabbits

The effect of different weaning ages, that is, 21 (G21), 28 (G28) or 35 (G35) days, on growth and certain parameters of the digestive tract was examined in rabbits to assess the risk of early weaning attributable to the less-developed digestive system. On days 35 and 42, G35 rabbits had 10% to 14% and 10% higher BW, respectively ( P,0.05), than those weaned at days 21 and 28. In the 4th week of life, early weaned animals had 75% higher feed intake than G28 and G35 rabbits ( P,0.05). The relative weight of the liver increased by 62% between 21 and 28 days of age, and thereafter it decreased by 76% between 35 and 42 days of age ( P,0.05), with G21 rabbits having 29% higher weight compared with G35 animals on day 35 ( P,0.05). The relative weight of the whole gastrointestinal (GI) tract increased by 49% and 22% after weaning in G21 and G28 rabbits, respectively ( P,0.05). On day 28, the relative weight of the GI tract was 19% higher in G21 than in G28 rabbits, whereas on day 35 G21 and G28 animals had a 12% heavier GI tract compared with G35 rabbits ( P,0.05). Age influenced the ratio of stomach, small intestine and caecum within the GI tract; however, no effect of different weaning age was demonstrated. The pH value of the stomach and caecum decreased from 5.7 to 1.6 and from 7.1 to 6.3, respectively, whereas that of the small intestine increased from 6.8 to 8.4 ( P,0.05); the differences between groups were not statistically significant. Strictly anaerobic culturable bacteria were present in the caecum in high amounts (108), already at 14 days of age; no significant difference attributable to weaning age was demonstrable. The concentration of total volatile fatty acids (tVFA) was higher in G21 than in G28 and G35 throughout the experimental period ( P,0.05). The proportion of acetic and butyric acid within tVFA increased, whereas that of propionic acid decreased, resulting in a C3 : C4 ratio decreasing with age. Early weaning (G21) resulted in higher butyric acid and lower propionic acid proportions on day 28 ( P,0.05). No interaction between age and treatment was found, except in relative weight of the GI tract and caecal content. In conclusion, early weaning did not cause considerable changes in the digestive physiological parameters measured, but it resulted in 10% lower growth in rabbits