Hypoxia influences expression profile of Pleckstrin homology-like domain, family A, member 2 in Indian catfish, Clarias batrachus (Linnaeus, 1758): A new candidate gene for hypoxia tolerance in fish.

Several physiologically important genes were found to be regulated by hypoxia at the transcriptional level. The Pleckstrin homology-like domain, family A, member 2 (PHLDA2) gene was previously identified as an imprinted gene. The present study was aimed to determine the structure of complete cDNA and the deduced protein of PHLDA2 along with analysing the changes in its mRNA expression in Clarias batrachus tissues under hypoxic conditions. The complete cDNA of CbPHLDA2 gene consisted of 1009 nucleotides with an open reading frame of 417 nucleotides. The deduced CbPHLDA2 protein of 139 amino acids shared high homology with PHLD2A of other fishes as well as that of vertebrates. Importantly, a single amino acid (asparagine/lysine) insertion was identified in the PH domain of CbPHLDA2 and other fishes, which was absent in other vertebrates studied. Furthermore, under normoxic conditions, CbPHLDA2 was constitutively expressed with varying levels in analysed tissues. Short- and long-term hypoxia exposure resulted in significant changes in the expression of CbPHLDA2 in liver, spleen, head kidney, brain and muscle in a time-dependent manner. The results suggested that CbPHLDA2 might play an important role for adaptive significance under hypoxia.

Physiological responses to acute experimental hypoxia in the air-breathing Indian catfish, Clarias batrachus (Linnaeus, 1758).

With an aim to study the mechanism of adaptation to acute hypoxic periods by hypoxia-tolerant catfish, Clarias batrachus, the mass-specific metabolic rate (VO2) along with its hematological parameters, metabolic response and antioxidant enzyme activities were studied. During progressive hypoxia, C. batrachus was found to be an oxyconformer and showed a steady decline in its aquatic oxygen consumption rate. When C. batrachus was exposed for different periods at experimental hypoxia level (0.98±0.1 mg/L, DO), hemoglobin and hematocrit concentrations were increased, along with decrease in mean cellular hemoglobin concentration, which reflected a physiological adaptation to enhance oxygen transport capacity. Significant increase in serum glucose and lactate concentration as well as lactate dehydrogenase activity was observed. Antioxidant enzymes were found to operate independently of one another, while total glutathione concentration was unaffected in any of the tissues across treatments. These observations suggested that hypoxia resulted in the development of oxidative stress and C. batrachus was able to respond through increase in the oxygen carrying capacity, metabolic depression and efficient antioxidant defense system to survive periods of acute hypoxia.

Transmission of male recombination, segregation distortion and sex-ratio imbalance in Drosophila melanogaster.

From the first test cross progenies of control (no larval transfers; no ethyl methanesulphonate), physical stress (two larval transfers; no ethyl methanesulphonate) and 0·75% ethyl methanesulphonate (two larval transfers; 0·75% ethyl methanesulphonate)- treated F1 (Oregon Κ + /dumpy black cinnabar, dp b cn) males of Drosophila melanogaster, respectively, 6,10 and 52 wild-looking first test cross males were again test crossed to obtain second generation. The overall percentages of male recombination detected in the second test cross progenies, in the three sets of experiments, were statistically the same as those in the first test cross progenies. Thus the enhanced male recombination caused by physical stress (with or without ethyl methanesulphonate) was transmitted to next generation. Non-reciprocal male recombination was observed in dp b but not in b cn region in both first and second test cross progenies. Three abnormalities, (i) production of wild-type flies in majority over dp b cn type, (ii) Non-Mendelian segregation at dp b and cn loci and (iii) sex-ratio differences for dp b cn and + b cn types observed in test cross progenies of F1 males of Drosophila melanogaster were transmitted to next generation when induced with 0·75 % ethyl methanesulphonate but not when these abnormalities were induced with physical stress. The data suggest possible association of non-reciprocal male recombination, segregation distortion and sex-ratio imbalance in Drosophila melanogaster. In fact these may be representing different aspects of the same phenomenon.