All posts by Kripa V. Jalapathy

Fungal pathogen loses “jumping genes” to gain stability and virulence

In the disease world of fungal pathogens, Cryptococcus neoformans is known to cause havoc among the immunocompromised individuals. Recently another sister fungal pathogen Cryptococcus deuterogattii has sickened hundreds of otherwise healthy people. Researchers around the world proposed that loss or gain of a whole bunch of genes could have been the key behind acquired virulence attributes. In a recent paper published in PNAS, Jawaharlal Nehru Centre for Advanced Scientific Research (JNCASR), Bangalore, India in collaboration with Duke University established a link between the loss of RNA interference ((RNAi) genes, reduction in the centromere length and gaining virulence attributes in Cryptococcus deuterogattii.

Sitting at the waistline of chromosomes, the centromere is an essential stretch of DNA that is required for accurate chromosome segregation, and to maintain genome stability. The researchers at JNCASR have been working on understanding the evolution of centromeres in human fungal pathogens for over a decade. In the current study published in PNAS, a team led by Prof. Kaustuv Sanyal identified centromeres in three closely related Cryptococcus species, assembled the genome at the chromosome level and scrutinized the centromeres. Remarkably, the team found a correlation between the centromere length and the presence of RNAi genes that are known to play a vital role in regulating genome and their stability. The two RNAi-proficient Cryptococcus species have large and complex centromeres with full-length DNA sequences called retrotransposons. These segments of DNA can jump around to different positions in the genome and cause mutations or increase (or decrease) amount of DNA. On the other hand, the RNAi-deficient Cryptococcus deuterogattii harbours smaller centromeres without full length or inactive retrotransposons. “We believe that shortening of centromeres in Cryptococcus deuterogattii led to its genome shrinkage that provided a replicative advantage in terms of faster growth rate, possibly contributing towards enhanced virulence of this species” said Prof. Sanyal, lead author and Professor at JNCASR.

RNAi is known to suppress transcription at the centromere. One would imagine that due to the loss of RNAi, transposons present at the centromere would have run wild in the genome! “In contrast, we see that they are in essence gone. The model is that the only way to survive the loss of RNAi may have been to get rid of the transposons from the genome or inactivate them so they cannot transpose anymore” says Vikas Yadav, first author of the study. To understand this, the team experimentally recreated the evolution in the lab by growing RNAi- proficient and RNAi-deficient strains for 1000 generations. Upon sequencing the genomes of these strains, it was seen that in the RNAi deficient strains, the retrotransposons at the centromere had undergone recombination causing shortening of centromeres. This is contrary to earlier studies from elsewhere that reported the suppression of recombination at centromere loci. Results of the current study suggest a role of RNAi in the evolution of centromeres. The team aims to extend the study to understand the impact of genomic changes on pathogenesis and virulence.

This work is a result of a long-term collaboration between the team JNCASR, Joseph Heitman’s group at Duke University Medical Center, USA, Christina Cuomo at Broad Institute of MIT & Harvard (USA) and Guus Bakkeren at Summerland Research and Development Centre, BC, Canada.

This research is funded by JNCASR, National Institutes of Health/National Institute of Allergy and Infectious Diseases, USA, and Tata Innovation Fellowship of Department of Biotechnology, Govt of India.

This article is authored by Kripa V. Jalapathy, Technical Research Centre (TRC), JNCASR.

Journal reference:

  1. Vikas Yadav, Sheng Sun, R. Blake Billmyre, Bhagya C. Thimmappa, Terrance Shea, Robert Lintner, Guus Bakkeren, Christina A. Cuomo, Joseph Heitman, Kaustuv Sanyal. RNAi is a critical determinant of centromere evolution in closely related fungi. Proceedings of the National Academy of Science USA. Mar 2018, 201713725; DOI: 1073/pnas.1713725115

Organic Electronics: Sensors with a flexible future

Organic Electronics: Sensors with a flexible future

In the “Internet of things” era, electronics are embedded in objects and transfer data without human intervention.  BP monitoring bands, non-contact cardiac sensors, glucose monitoring medical sensors, driverless cars and electronic wallpaper and gadgets are slowly refining and evolving our lifestyle.  Well, these are probably just a few of the possible future applications that are being enabled by solution processible/printable electronic and opto-electronic materials.

The availability of softer materials such as organics and polymers which respond to light and emit light, accompanied by reasonable electrical transport properties provide us with options in the world dominated silicon electronics. There has been growing need for niche applications where there are requirements for flexible-stretchable-bendable smart sensors and display elements.

With the aim to provide an alternative to the conventional silicon based silicon photo-detector approach, researchers at Jawaharlal Nehru Center for Advanced Scientific Research (JNCASR) have used a light-sensitive organic compound while the read-out electronics have been fabricated on a polymer organic thin-film transistor backplane. By developing an integrated organic electronic component similar to a CMOS pixel fabricated by printing methods for image sensing applications, Prof. K S Narayan’s lab at the Chemistry and Physics of Material Unit (CPMU) department of JNCASR have made strides in combining organic thin-cell transistor backplane with a organic photodiode layer which is printed on polymer substrate. Since the components of the organic circuit are deposited from solution phase, they can be sprayed or coated on flexible or stretchable substrates. In a recent article that was published in Applied Physics Letters, the researchers have shown that the optoelectronic response of the photodiode (with polymer based semiconductors) was large and sufficient to control the field effect transistor consisting of the polymer semiconductor. The highlight of the results is the demonstration of an organic electronics circuit with an efficient light sensing photodiode and a low turn-ON field effect transistor (FET). It was shown that the output characteristics of the FET were dependent on the light-level incident on the photodiode.


Prof. Narayan says “the possibility of fabricating circuits by simple dispensing methods with response equivalent to elaborate Si based structures which require complex manufacturing requirements is interesting, and the added features of such devices over large-area on non-rigid and flexible substrates provides some exciting applications in life sciences and ambient electronics sensors. We have some novel strategies to further increase the spatial resolution and the sensitivity of the organic pixel element.”

We have developed a method of spraying or coating of the polymer based substrates, and we believe the method will enable distributed sensor arrays over larger areas than that achievable for silicon-based processes. We will be interested in fabricating a large-area prototype and explore the feasibility in real world applications noted Ms. Swati, PhD scholar in Prof. Narayan’s lab. who spearheads this activity.

This article is authored by Kripa V. Jalapathy, Technical Research Center (TRC), JNCASR.


  1. Swathi, and K. S. Narayan Image pixel device using integrated organic electronic components Appl. Phys. Lett. 109, 193302 (2016)
  2. Swathi, K.S. Narayan, Solution processed integrated pixel element for an imaging device, Proc. SPIE 9944, Organic Sensors and Bioelectronics IX, 99440T (September 27, 2016)