University of Peradeniya

About: University of Peradeniya is a education organization based out in Kandy, Sri Lanka. It is known for research contribution in the topics: Population & Poison control. The organization has 5970 authors who have published 7388 publications receiving 197002 citations.

Barriers to tree seedling emergence on human-induced grasslands in Sri Lanka

Abstract: Summary 1. Colonization by woody plants is often very slow or absent on grasslands occupying degraded land in the tropics. Seed dispersal limitation is widely reported, but the constraints to forest succession imposed by barriers to seedling establishment are poorly understood. We tested the hypotheses that seedling emergence of woody plants is limited by interactions of anthropogenic fire, vertebrate herbivory and competition with the dominant grass sward in human-induced montane grasslands in Sri Lanka. 2. Seedling emergence was determined fortnightly for 18 months in response to experimental manipulation of fire regimes, access by vertebrate herbivores and competition from the dominant grass canopy at the forest/grassland edge and at 10, 20 and 40 m from the edge into four blocks of grassland. Seedling emergence was also monitored in the absence of any experimental manipulation at 10, 20 and 40 m into adjacent blocks of lower montane rainforest. 3. Emergence of seedlings of woody plants was much lower in the grassland (mean <0·1 seedlings m−2 year−1) than in natural forest patches (mean 6·0 seedlings m−2 year−1), but was maximal at the forest/grassland edge (mean 9·5 m−2 year−1). In the grassland, fire reduced seedling emergence by 36% in fenced vertebrate exclosures but increased seedling emergence by 68% in unfenced plots. Exclusion of vertebrate herbivores had no impact on seedling emergence at the forest/grassland edge. Removal of the grass canopy by clipping or tilling increased seedling emergence at the edge, but had no effect in the grassland. Seedlings of the woody pioneer species Macaranga indica dominated the community of emergents in the grassland and at the edge. 4. Synthesis and applications. Although dispersal limitation represents the primary constraint to forest succession on degraded montane grasslands in Sri Lanka, management of fire regimes, vertebrate herbivory and competition from the dominant grasses would influence the abundance and composition of tree seedling emergents. Tilling in narrow strips, 2–5 m wide and within 10 m of the forest edge, would facilitate the emergence and establishment of early successional trees in the grassland, but the strips would require protection from fire for at least 2 years. Within the interior of grassland patches, a combination of controlled burning and short-term access to vertebrate dispersers would promote tree seedling emergence, but the burned patches would then require long-term protection from fire and grazing subsequently to allow the emergents to establish and catalyse forest succession.

MicroRNA Let-7a and dicer are important in the activation and implantation of delayed implanting mouse embryos

Abstract: Study question Does Let-7a have a functional role in modulating dicer expression to activate dormant mouse blastocysts for implantation? Summary answer Let-7a post-transcriptionally regulates dicer expression altering microRNA expression to affect the implantation competency of the activated blastocysts. What is known already The Let-7a microRNA is up-regulated during blastocyst dormancy and its forced-expression suppresses embryo implantation in vitro and in vivo. Dicer is a Let-7 target, which processes pre-microRNA to mature microRNA. Study design, size, duration The effects on the expression of Let-7a and dicer in dormant blastocysts during the first 12 h after estradiol-induced activation, and the relationship between Let-7a and dicer in preimplantation embryos were determined. The effects on the microRNA expression and embryo implantation in vivo in dicer-knockdown mouse 5-8 cell embryos and dormant blastocysts at 1 h post estradiol activation were also studied. Participants/materials, setting, methods ICR female mice at 6 weeks of age were ovariectomized on Day 4 of pregnancy to generate the delayed implantation model. Mouse 5-8 cell embryos and/or dormant blastocysts at 1 h after estradiol injection were electroporated with dicer siRNA and Let-7a precursor or Let-7a inhibitor. At 48 h post electroporation, the Let-7a expression, dicer transcripts and proteins in the embryos were determined using qPCR and immunostaining/western blotting, respectively. All experiments were repeated at least three times. Main results and the role of chance Estradiol injection down-regulated Let-7a and up-regulated dicer in the dormant blastocysts during the first 12 h post-activation. Dicer knockdown at 1 h post-activation of blastocysts suppressed EGFR expression, attenuated EGF binding and compromised implantation of the transferred embryos. Let-7a transcriptionally regulated dicer by binding to the 3'-UTR of dicer in trophoblast cells. Dicer knockdown in blastocysts suppressed mature Let-7a expression and compromised implantation. Limitations, reasons for caution Gain- and loss-of-function approaches were used by analyzing transient expressions of transfected microRNA modulators or genes. The consequence of the Let-7a-dicer interaction on pregnancy remains to be determined. The study used the mouse as a model and the applicability of the observed phenomena in humans warrants further investigation. Wider implications of the findings Our results indicate that the Let-7a-dicer interaction leads to differential microRNA expression in dormant blastocysts after estradiol activation. Because the expression pattern of Let-7a in human blastocysts is similar to that in mouse blastocysts, our observation that the Let-7a-dicer interaction has a role in regulating the implantation potential of the mouse blastocysts could be applicable to humans. Study funding/competing interest(s) This project is supported partly by a research grant from the Research Grant Council to W.S.B.Y. The authors have no competing interests to declare.