Now showing 1 - 10 of 40
  • Publication
    Open Access
      45  33
  • Publication
    Open Access
    A comparative study on undergraduates’ and graduates’ perceptions of teaching and learning
    (1994-11) ;
    Wong, Patricia J. Y.
    In order to refine teaching styles and methods of assessing students' learning, it is important to realise the perceptions different schools hold about teaching and learning. Thus, this study was undertaken to compare students in the Bachelor of Science with Diploma in Education (Secondary) programme (PGDE) on their perceptions of the desirable characteristics of a "good" lecturer, their preferences of teaching methods and student assessment, their motives for taking the course and their learning styles employed. The results indicate that both groups of students were genuinely interested in the courses they enrolled in. Although there was a high degree of unanimity among students in their conception of a "good" lecturer and their preferred learning styles, the PGDE students preferred lecturers who were more expressive. In addition, the PGDE students were more independent in their learning than the BSC students. The findings of the present study may serve to kindle some genuine ideas among lecturers on how to improve the quality of teaching and learning in the University.
      146  105
  • Publication
    Open Access
    Aestivation induces changes in transcription and translation of coagulation factor II and fibrinogen gamma chain in the liver of the African lungfish Protopterus annectens
    (2015)
    Hiong, Kum Chew
    ;
    Tan, Xiang Ru
    ;
    Boo, Mel Veen
    ;
    Wong, Wai Peng
    ;
    ;
    Ip, Yuen Kwong
    This study aimed to sequence and characterize two pro-coagulant genes, coagulation factor II (f2) and fibrinogen gamma chain (fgg), from the liver of the African lungfish Protopterus annectens, and to determine their hepatic mRNA expression levels during three phases of aestivation. The protein abundance of F2 and Fgg in the liver and plasma was determined by immunoblotting. The results indicated that F2 and Fgg of P. annectens were phylogenetically closer to those of amphibians than those of teleosts. Three days of aestivation resulted in an up-regulation in the hepatic fgg mRNA expression level, while 6 days of aestivation led to a significant increase (3-fold) in the protein abundance of Fgg in the plasma. Hence, there could be an increase in the blood-clotting ability in P. annectens during the induction phase of aestivation. By contrast, the blood-clotting ability in P. annectens might be reduced in response to decreased blood flow and increased possibility of thrombosis during the maintenance phase of aestivation, as 6 months of aestivation led to significant decreases in mRNA expression levels of f2 and fgg in the liver. There could also be a decrease in the export of F2 and Fgg from the liver to the plasma so as to avert thrombosis. Three to 6 days after arousal from 6 months of aestivation, the protein abundance of F2 and Fgg recovered partially in the plasma of P. annectens; a complete recovery of the transcription and translation of f2/F2 in the liver might occur only after refeeding.
    WOS© Citations 10Scopus© Citations 10  145  227
  • Publication
    Open Access
    Air-breathing and excretory nitrogen metabolism in fishes
    (2018)
    Ip, Yuen Kwong
    ;
    During water-land transition, ancient fishes acquired the ability to breathe air, but air-breathing engendered problems in nitrogenous waste excretion. Nitrogen is a fundamental component of amino acids, proteins, and nucleic acids, and the degradation of these nitrogen-containing compounds releases ammonia. Ammonia is toxic and must be removed. Fishes in water excrete ammonia as the major nitrogenous waste through gills, but gills of air-breathing fishes are modified for air-breathing or largely replaced by air-breathing organs. Notably, fishes emerged from water can no longer excrete ammonia effectively because of a lack of water to flush the gills. Hence, ancient fishes that participated in water-land transition must have developed means to deal with ammonia toxicity. Extant air-breathing fishes, particularly amphibious ones, can serve as models to examine adaptations which might have facilitated the emergence of ancient fishes from water. Some of these fishes can actively emerge from water and display complex behaviors on land, while a few can burrow into mud and survive for years during drought. Many of them are equipped with mechanisms to ameliorate ammonia toxicity during emersion. In this review, the mechanisms adopted by air-breathing fishes to deal with ammonia toxicity during emersion were organized into seven disparate strategies. In addition, eight extant air-breathing fishes with distinctive terrestrial behaviors and peculiar natural habitats were selected to describe in detail how these seven strategies could be adopted in disparate combinations to ameliorate ammonia toxicity during emersion.
    WOS© Citations 43Scopus© Citations 47  181  164
  • Publication
    Open Access
    The fluted giant clam (Tridacna squamosa) increases the protein abundance of the host's copper-zinc superoxide dismutase in the colorful outer mantle, but not the whitish inner mantle, during light exposure
    (2020) ;
    Koh, Clarissa Z. Y.
    ;
    Hiong, Kum Chew
    ;
    Boo, Mel Veen
    ;
    Wong, Wai Peng
    ;
    Ip, Yuen Kwong
    The colorful outer mantle of giant clams contains abundance of symbiotic dinoflagellates (zooxanthellae) and iridocytes, and has direct exposure to light. In light, photosynthesizing dinoflagellates produce O2, and the host cells in the outer mantle would be confronted with hyperoxia-related oxidative stress. In comparison, the whitish inner mantle contains few symbiotic dinoflagellates and no iridocytes. It is involved in shell formation, and is shaded from light. CuZnSOD is a cytosolic enzyme that scavenges intracellular O2"-. We had obtained from the outer mantle of the fluted giant clam, Tridacna squamosa, the complete cDNA coding sequence of a host-derived copper zinc superoxide dismutase (CuZnSOD), which comprised 462 bp and encoded for 154 amino acids with a calculated MW of 15.6 kDa. CuZnSOD was expressed strongly in the outer mantle, ctenidium, hepatopancreas and kidney. The transcript level of CuZnSOD remained unchanged in the outer mantle during light exposure, but the protein abundance of CuZnSOD increased ~3-fold after exposure to light for 6 or 12 h. By contrast, 12 h of light exposure had no significant effects on the gene and protein expression levels of CuZnSOD/CuZnSOD in the inner mantle. Hence, the increased expression of CuZnSOD in the outer mantle of T. squamosa was probably a host's response to ameliorate oxidative stress related to photosynthesis in the symbionts, and not simply due to increased metabolic rate in the host cells. Evidently, the host clam must possess light- or O2-responsive anti-oxidative defenses in order to align with the light-dependent photosynthetic activity of its symbionts.
    WOS© Citations 2Scopus© Citations 2  289  42
  • Publication
    Embargo
    Evidence for the involvement of branchial Vacuolar-type H+-ATPase in the acidification of the external medium by the West African lungfish, Protopterus annectens, exposed to ammonia-loading conditions
    (2022)
    Ip, Yuen Kwong
    ;
    Leong, Charmaine W. Q.
    ;
    Boo, Mel Veen
    ;
    Wong, Wai Peng
    ;
    Lam, Siew Hong
    ;
    African lungfishes are obligatory air-breathers with exceptionally high environmental ammonia tolerance. They can lower the pH of the external medium during exposure to ammonia-loading conditions. This study aimed to demonstrate the possible involvement of branchial vacuolar-type H+-ATPase (Vha) in the ammonia-induced acidification of the external medium by the West African lungfish, Protopterus annectens, and to examine whether its capacity to acidify the medium could be augmented after exposure to 100 mmol l−1 NH4Cl for six days. Two full coding cDNA sequences of Vha subunit B (atp6v1b), atp6v1b1 and atp6v1b2, were obtained from the internal gills of P. annectens. The sequence of atp6v1b1 comprised 1548 bp, encoding 515 amino acids (57.4 kDa), while that of atp6v1b2 comprised 1536 bp, encoding 511 amino acids (56.6 kDa). Using a custom-made antibody reactive to both isoforms, immunofluorescence microscopy revealed the collective localization of Atp6v1b (atp6v1b1 and atp6v1b2) at the apical or the basolateral membrane of two different types of branchial Na+/K+-ATPase-immunoreactive ionocyte. The ionocytes labelled apically with Atp6v1b presumably expressed Atp6v1b1 containing a PDZ-binding domain, indicating that the apical Vha was positioned to transport H+ to the external medium. The expression of Atp6v1b was regulated post-transcriptionally, as the protein abundance of Atp6v1b and Vha activity increased significantly in the gills of fish exposed to 100 mmol l−1 NH4Cl for six days. Correspondingly, the fish exposed to ammonia had a greater capacity to acidify the external medium, presumably to decrease the ratio of [NH3] to [NH4+] in order to reduce the influx of exogenous NH3.
    WOS© Citations 2Scopus© Citations 2  41  1
  • Publication
    Open Access
    Ammonia transporter 2 as a molecular marker to elucidate the potentials of ammonia transport in phylotypes of Symbiodinium, Cladocopium and Durusdinium in the fluted giant clam, Tridacna squamosa
    (2022)
    Pang, Caryn Zhiqin
    ;
    Ip, Yuen Kwong
    ;
    Giant clams harbor coccoid Symbiodiniaceae dinoflagellates that are phototrophic. These dinoflagellates generally include multiple phylotypes (species) of Symbiodinium, Cladocopium, and Durusdinium in disparate proportions depending on the environmental conditions. The coccoid symbionts can share photosynthate with the clam host, which in return supply them with nutrients containing inorganic carbon, nitrogen and phosphorus. Symbionts can recycle nitrogen by absorbing and assimilating the endogenous ammonia produced by the host. This study aimed to use the transcript levels of ammonia transporter 2 (AMT2) in Symbiodinium (Symb-AMT2), Cladocopium (Clad-AMT2) and Durusdinium (Duru-AMT2) as molecular indicators to estimate the potential of ammonia transport in these three genera of Symbiodiniaceae dinoflagellates in different organs of the fluted giant clam, Tridacna squamosa, obtained from Vietnam. We also determined the transcript levels of form II ribulose-1,5-bisphosphate carboxylase/oxygenase (rbcII) and nitrate transporter 2 (NRT2) in Symbiodinium (Symb-rbcII; Symb-NRT2), Cladocopium (Clad-rbcII; Clad-NRT2) and Durusdinium (Duru-rbcII; Duru-NRT2), in order to examine the potential of ammonia transport with reference to the potentials of phototrophy or NO₃− uptake independent of the quantities and proportion of these Symbiodiniaceae phylotypes. Our results indicated for the first time that phylotypes of Symbiodinium and Cladocopium could have different potentials of ammonia transport, and that phylotypes of Symbiodinium might have higher potential of NO₃− transport than ammonia transport. They also suggested that Symbiodiniaceae phylotypes residing in different organs of T. squamosa could have disparate potentials of ammonia transport, alluding to the functional diversity among phylotypes of coccoid Symbiodinium, Cladocopium, and Durusdinium.
    WOS© Citations 2Scopus© Citations 2  71  37
  • Publication
    Open Access
    The giant clam Tridacna squamosa quickly regenerates iridocytes and restores symbiont quantity and phototrophic potential to above-control levels in the outer mantle after darkness-induced bleaching
    (2021)
    Ip, Yuen Kwong
    ;
    Boo, Mel Veen
    ;
    Mies, Miguel
    ;
    Giant clams are ecologically and economically relevant reef inhabitants that host photosynthetic dinoflagellates inside tubules located mainly in their colorful outer mantle. This study examined the effects of exposure to darkness for 30 days and the subsequent 11 days of recovery under a normal photoperiod on the outer mantle of the fluted giant clam Tridacna squamosa. Changes in the abundance of iridocytes and symbionts were assessed by fluorescence microscopy. Light microscopy was applied to quantify symbionts isolated from the outer mantle, while chlorophyll was extracted and analyzed by spectroscopy. The transcript levels of the host’s vacuolar-type H+-ATPase subunit A (ATP6V1A) and symbionts’ form II ribulose-1,5-bisphosphate carboxylase/oxygenase (Zoox-rbcII) were determined by quantitative real-time PCR (qPCR) and used as proxies for iridocyte abundance and phototrophic potential, respectively. The protein abundance of ATP6V1A and Zoox-RBCII was quantified by western blotting. After exposure to darkness for 30 days, the outer mantle of T. squamosa individuals lost the distinct multiple color patterns, and the gene and protein expression levels of ATP6V1A/ATP6V1A and Zoox-rbcII/Zoox-RBCII decreased dramatically. Microscopy assessment confirmed the reduction in iridocyte and symbiont populations, and the chlorophyll level also decreased considerably. However, just 11 days after returning to a normal light:dark regimen, the quantity of coccoid dinoflagellates and the expression of Zoox-rbcII/Zoox-RBCII in the outer mantle increased significantly to levels higher than those of the individuals prior to exposure to darkness (control), while the chlorophyll content returned to the control level. Additionally, the outer mantle regained most of its coloration with partial recovery of the iridocyte population. These results are relevant not only for understanding the phenomena of light deprivation and symbiont loss in dinoflagellate-associated reef organisms, but also signify that the giant clam-coccoid dinoflagellate holobiont is phototrophically plastic and particularly tolerant to bleaching.
    WOS© Citations 2Scopus© Citations 2  91  63