Bone morphogenetic protein and retinoic acid signaling cooperate to induce osteoblast differentiation of preadipocytes

Mesenchymal cells can differentiate into osteoblasts, adipocytes, myoblasts, or chondroblasts. Whether mesenchymal cells that have initiated differentiation along one lineage can transdifferentiate into another is largely unknown. Using 3T3-F442A preadipocytes, we explored whether extracellular signals could redirect their differentiation from adipocyte into osteoblast. 3T3-F442A cells expressed receptors and Smads required for bone morphogenetic protein (BMP) signaling. BMP-2 increased proliferation and induced the early osteoblast differentiation marker alkaline phosphatase, yet only mildly affected adipogenic differentiation. Retinoic acid inhibited adipose conversion and cooperated with BMP-2 to enhance proliferation, inhibit adipogenesis, and promote early osteoblastic differentiation. Expression of BMP-RII together with BMP-RIA or BMP-RIB suppressed adipogenesis of 3T3-F442A cells and promoted full osteoblastic differentiation in response to retinoic acid. Osteoblastic differentiation was characterized by induction of cbfa1, osteocalcin, and collagen I expression, and extracellular matrix calcification. These results indicate that 3T3-F442A preadipocytes can be converted into fully differentiated osteoblasts in response to extracellular signaling cues. Furthermore, BMP and retinoic acid signaling cooperate to stimulate cell proliferation, repress adipogenesis, and promote osteoblast differentiation. Finally, BMP-RIA and BMP-RIB induced osteoblast differentiation and repressed adipocytic differentiation to a similar extent

Roles of Autocrine TGF-β Receptor and Smad Signaling in Adipocyte Differentiation

TGF-β inhibits adipocyte differentiation, yet is expressed by adipocytes. The function of TGF-β in adipogenesis, and its mechanism of action, is unknown. To address the role of TGF-β signaling in adipocyte differentiation, we characterized the expression of the TGF-β receptors, and the Smads which transmit or inhibit TGF-β signals, during adipogenesis in 3T3-F442A cells. We found that the cell-surface availability of TGF-β receptors strongly decreased as adipogenesis proceeds. Whereas mRNA levels for Smads 2, 3, and 4 were unchanged during differentiation, mRNA levels for Smads 6 and 7, which are known to inhibit TGF-β responses, decreased severely. Dominant negative interference with TGF-β receptor signaling, by stably expressing a truncated type II TGF-β receptor, enhanced differentiation and decreased growth. Stable overexpression of Smad2 or Smad3 inhibited differentiation and dominant negative inhibition of Smad3 function, but not Smad2 function, enhanced adipogenesis. Increased Smad6 and Smad7 levels blocked differentiation and enhanced TGF-β–induced responses. The inhibitory effect of Smad7 on adipocyte differentiation and its cooperation with TGF-β was associated with the C-domain of Smad7. Our results indicate that endogenous TGF-β signaling regulates the rate of adipogenesis, and that Smad2 and Smad3 have distinct functions in this endogenous control of differentiation. Smad6 and Smad7 act as negative regulators of adipogenesis and, even though known to inhibit TGF-β responses, enhance the effects of TGF-β on these cells

Ecological studies of Medium to large mammals in oil palm plantation, Miri, Sarawak

Good or evil? Palm oil has always been in the centre of a decade long controversy. While it contributes to the economy, alleviates poverty and is by far the most land-efficient oil crop, it comes at the cost of local ecosystems and devastates lands which are highly biodiverse such as Borneo (Laurence et al., 2014). Approximately 12.5% of the land in Sarawak has already been converted to oil palm plantations (MPOB, 2017). Monocrops have proved to be much lower in biodiversity compared to forested areas as it lacks necessary resources for many species. Despite efforts from the Roundtable of Sustainable of Oil Palm (RSPO) to push for sustainable oil palm practices such as maintaining High Conservation Value Forest (HCVF), knowledge gaps on the effects of management practices towards the local fauna still exists and comprehension on the carrying capacities of the oil palm are still limited. It is therefore critical to conservation to figure out how to improve oil palm plantation to be more hospitable to wildlife. Among the most threatened taxonomic group due to fragmentation are mammals as they are highly sensitive to anthropogenic pervasion to and into their habitats. Medium to large mammals were selected as a focus group in this study as they are regarded as keystone species and are excellent bioindicators for healthy ecosystems. A one-year long camera trap survey of medium to large mammals is currently being conducted to provide baseline data on mammalian diversity and its persistence within the HCV forest fragments and oil palm matrix in regards to management practices for management decision. We have recorded various species of conservation importance in forest fragments. This includes the Sunda Pangolin (Manis javanica), Sun Bear (Helarctos malayanus) and Sambar Deer (Rusa unicolor). An adaptive management plan and integrated conservation strategy will be formulated at the end of the project to contribute to the preservation, sustenance and enhancement of the HCVF areas and in the oil palm areas

Medium to Large Terrestrial Mammals

Mammals are one of the most susceptible taxa to local extinction because of habitat fragmentation and loss (Dirzo et al., 2014). Partly due to their sensitivity to their surrounding, mammals are often used for biodiversity assessments and monitoring programmes around the globe as they are reliable ecosystem quality indicators (Ahumuda et al., 2011). However, as tropical medium to large mammals are often cryptic and elusive in nature (Mohd-Azlan, 2006), they are difficult to study. Therefore comprehension of the persistence of medium to large mammals within forest fragments especially in agricultural landscapes in this region is important as they remain scarce in scientific literature. Remnant forest fragments within the plantation area may potentially provide refugia and support the existence of medium to large mammals as many studies have indicated that oil palm plantation harbours lower diversity of wildlife compared to forested areas

Latitudinal variation in ecological opportunity and intraspecific competition indicates differences in niche variability and diet specialization of Arctic marine predators

Individual specialization (IS), where individuals within populations irrespective of age, sex, and body size are either specialized or generalized in terms of resource use, has implications on ecological niches and food web structure. Niche size and degree of IS of near-top trophic-level marine predators have been little studied in polar regions or with latitude. We quantified the largescale latitudinal variation of population- and individual-level niche size and IS in ringed seals (Pusa hispida) and beluga whales (Delphinapterus leucas) using stable carbon and nitrogen isotope analysis on 379 paired ringed seal liver and muscle samples and 124 paired beluga skin and muscle samples from eight locations ranging from the low to high Arctic. We characterized both withinand between-individual variation in predator niche size at each location as well as accounting for spatial differences in the isotopic ranges of potential prey. Total isotopic niche width (TINW) for populations of ringed seals and beluga decreased with increasing latitude. Higher TINW values were associated with greater ecological opportunity (i.e., prey diversity) in the prey fish community which mainly consists of Capelin (Mallotus villosus) and Sand lance (Ammodytes sp.) at lower latitudes and Arctic cod (Boreogadus saida) at high latitudes. In beluga, their dietary consistency between tissues also known as the within-individual component (WIC) increased in a near 1:1 ratio with TINW (slope = 0.84), suggesting dietary generalization, whereas the slope (0.18) of WIC relative to TINW in ringed seals indicated a high degree of individual specialization in ringed seal populations with higher TINWs. Our findings highlight the differences in TINW and level of IS for ringed seals and beluga relative to latitude as a likely response to large-scale spatial variation in ecological opportunity, suggesting species-specific variation in dietary plasticity to spatial differences in prey resources and environmental conditions in a rapidly changing ecosystem

Small Mammals

The Bornean tropical rainforests harbour some of the most remarkable diversity of flora and fauna in the world (Jennings et al., 2015; Sodhi et al., 2004). Tropical biodiversity is highly threatened by land conversion for agricultural purposes. This calls for greater conservational prioritization (Wilcove & Koh, 2010; Fitzherbert et al., 2008) as many have become fragmented and disconnected. There are a total of 247 species of mammals recorded in Borneo, and small mammals make up approximately 81%, which can be sub-categorized into bats, shrews, treeshrews, rats, mice, squirrels and flying squirrels (Phillipps & Phillipps, 2016). Borneo is regarded as one of the biodiversity hotspots, sustaining a high concentration of endemism, including approximately 19% of mammals (5% of the 99 bats species and 26 Rodentia), 20% of snakes and 6% of birds (Mohd-Azlan & Lawes, 2011).