K. C. Majumdar

Thyroid hormone modulation of ovarian recrudescence of air-breathing catfish Clarias gariepinus

In the present study, thiourea-induced thyroid hormone depletion and thyroxine (T4) ‘overdose’ were used as a strategy to understand the influence of thyroid hormones on ovarian recrudescence of juvenile (3-months-old), immature (8-months-old) and adult (1-year-old) air-breathing catfish, Clarias gariepinus. Thiourea-induced thyroid hormone depletion in juvenile catfish impaired ovarian development, but no significant effect was observed in immature catfish and during late stage of ovarian recrudescence of mature catfish. T4 treatment in females undergoing late stages of ovarian recrudescence induced rapid oocyte growth by promoting its early entry into maturational phase as evident from the presence of more number of vitellogenic and post-vitellogenic follicles, decrease in aromatse immunoreactivity and reduced estradiol-17β levels. Hence, thyroid hormones have an important role to play during early stages of ovarian development and vitellogenesis of catfish and also indicating that thyroid has a stage dependent effect on ovary.

Replication of DNA in larval salivary glands of Drosophila after in vivo synchronization

The replication of DNA in the giant chromosomes in different cells of Drosophila larval salivary glands is asynchronous. A method of in vivo synchronization of the nuclei has been successfully devised by a 5′-fluorodeoxyuridine (FdU) block-release-thymidine chase technique, and the patterns of replication sequences have been examined by 3H-thymidine autoradiography. When the larvae of Drosophila melanogaster are fed on FdU for 48 h, and the block is released thereafter, most cells are found in mid-replication phase (termed 3C). When the larvae are subjected to a chase in normal Drosophila medium (or sucrose), a series of cells arrive at 3C phase about every 8 h. When they are chased in sucrose containing thymidine, the number of cells in 3C phase rises to 70%, and then drops rapidly to 1–2% of all labelled cells. The terminal phases (3D, 2D and 1D) reach a peak between 4–8 h. At 12–14 h of chase the 3D-1D peaks decline and a third peak consisting mostly of the initial phases (DD-1C) is found at 14–16 h. The replication of DNA in polytene chromosomes of Drosophila thus seems to proceed in a regular sequence of DD-3C-1D.

Transgene integration - an analysis in autotransgenic Labeo rohita Hamilton (Pisces: Cyprinidae).

Transgenic Labeo rohita founder population was analyzed for the presence of autotransgene having histone 3 promoter and growth hormone (GH) cDNA (LRH3-GHcDNA) or total GH gene (LRH3-GH2.8) by PCR with transgene specific primers. Transgene specific amplification was seen with LRH3-GHcDNA in five out of seven individuals and all three fishes with LRH3-GH2.8, indicating their transgenic nature. Transgene integration was also studied by Southern hybridization of DNA isolated from blood of the transgenic fishes with two different probes (histone 3 promoter and cDNA of L. rohita). Autotransgene integration was confirmed in all PCR positive transgenic individuals. The site of integration of the transgene in the genome of the four transgenic fish could be determined by inverse PCR. Two individuals showed integration at the same site whereas in the remaining two individuals the integration sites were different.

Sex specific chromosome polymorphisms in the common Indian Krait, Bungarus caeruleus Schneider (Ophidia, Elapidae)

Chromosome analyses of common Indian Krait, B. caeuleus from three geographical regions of India have revealed variable diploid numbers of 43, 44 and 45 in different female individuals but a constant diploid number of 44 in the males. C-banding and in situ hybridization studies, using radio labelled W sex chromosome specific satellite DNA as a probe, have shown that C-banding and sex chromosome associated satellite DNAs are exclusively localised in the W chromosome. The W chromosome is involved in reciprocal translocations either with a medium sized macroautosome or with a microchromosome resulting in a multiple sex chromosome constitution of Z1Z1Z2Z2♂/Z1Z2W♀ type. In some female individuals dissociation of the W has resulted in multiple W chromosomes, W1 and W2. These polymorphisms are uniquely confined to the female sex only. A predominance of polymorphic females, involving particularly the translocation of a medium sized macrochromosome, in all three geeographical regions and the restriction of the females having the original chromosome constitution (ZW) to one geographical region suggests that polymorphic individuals have adaptive flexibility and higher fecundity.

31P Nuclear Magnetic Resonance Studies on the Phosphorus-Containing Metabolites of the Developing Embryos of a Freshwater Catfish, Clarias batrachus (L.)

Abstract: Changes in the phosphorus-containing metabolites were monitored by 31P nuclear magnetic resonance in the developing embryos of Clarias batrachus. Phosphomonoester, yolk phosphoprotein, phosphocreatine, ATP, and inorganic phosphate (Pi) were consistently observed in all the developmental stages of C. batrachus. None of these phosphometabolites exhibited any significant change in their concentration up to the blastula stage, whereas distinct decrease in all except inorganic phosphate was observed in the fry stage. Concomitantly an increase in the concentration of inorganic phosphate was observed. Further, from the resonance positions of α, β, and γ phosphate groups of ATP, it was evident that the ATP molecules in vivo were liganded either to Ca2+ or Mg2+. This study also revealed that the intracellular pH of the developing embryos was approximately 7.05 up to the gastrula stage, after which it decreased in the fry stage to 6.98 units.

Reconstruction of phylogenetic relationships

In this paper, we provide an introductory overview to the field of phylogenetic analysis, which has wide applications in modern biology.

Behaviour of microchromosome-associated satellite DNA in the banded krait,Bungarus fasciatus (Ophidia, Elapidae)

Banded krait(Bungarus fasciatus) major satellite DNA (p = 1.700 g/cm3) is mainly localized in the C-band-positive regions of all the microchromosomes. Our study of the behaviour of this satellite DNA byin situ hybridization has revealed a striking polarization of this DNA in the follicular epithelial cells of the ovary during oogenesis and in the spermatids during spermiogenesis. The major satellite DNA is localized at the point of the subsequent protrusion of the acrosomal pole of the round spermatid nuclei and remains in close contact with the developing sperm tip during the process of spermiogenesis. There appears to be an attraction between a specific region of the nuclear membrane and satellite-rich chromatin of the microchromosomes that brings about their polarization. We discuss possible functions of such extreme polarization of microchromosomes in specific cell types during oogenesis and spermiogenesis.

Effect of thyroid hormone depletion on monoamines and expression patterns of catfish GnRH in the air-breathing catfish, Clarias gariepinus

Thyroid hormone is known to have profound effect on the efficient functioning of the reproductive system. The GnRH-gondaotropin (GTH) axis is the crucial axis involved in regulation of the various aspects of reproduction like spermatogenesis, synthesis of sex steroids and regulation of courting and spawning behavior. Earlier study from our laboratory has shown that thyroid hormone depletion causes a decrease in GTH and GnRH levels in pituitary and preoptic area, respectively. GnRH secretion in pre-optic area is largely regulated by the monoaminergic system mainly dopamine (DA), epinephrine (E), norepinephrine (NE) and serotonin (5-HT). The expression pattern of catfish GnRH transcripts tends to corroborate our earlier findings. Hence, in the current study we aimed to investigate the levels of monoamines in the preoptic area-hypothalamus (POA-H), so as to determine whether thyroid hormone depletion modulates the monoaminergic neurotransmission thereby affecting GnRH secretion. The levels of NE and L-dopa decreased significantly while that of DA was unaltered following thyroid hormone depletion. DA has an inhibitory effect on GnRH secretion. Findings from the present study suggest that the inhibitory tone is unaltered while the stimulatory tone influencing GnRH neurons in POA-H is decreased during thiourea induced thyroid hormone depletion.