Page 64 - Biennial Report 2018-20 Jun 2021

were significantly upregulated. However, all further experiments pointed towards absence of
toxicity or inflammation due to CAG repeat RNA. For instance, CAG repeat RNA alone did not
lead to the release of interferon gamma or cell death. Besides in vitro transcribed CAG repeat
RNA, the repeats were presented in the context of a non-translatable mutant gene but led to
similar results. Although polyglutamine mediated protein toxicity was long held to be the
causative agent in certain neurodegenerative diseases, more recent evidence implicated the
CAG repeat RNA that encodes the polyglutamine stretch. Atleast in the context of
Spinocerebellar Ataxia 17 caused by Cag repeat expansion in TATA binding protein, the role of
RNA toxicity was ruled out.

MECHANISTIC BASIS OF IncRNA MEDIATED REGULATION IN ORGAN

DEVELOPMENT AND FUNCTION

It was established previously in Beena Pillai’s laboratory that Cyrano RNA is parentally inherited,
and the selective loss of the maternally inherited component is sufficient to cause brain
morphology defects in about 70% of the embryos. Over-expression of Durga RNA, on the other
hand, resulted in increased Kalirn expression and reduced dendritogenesis that was evident from
the decrease in the number and length of dendrites. In the reporting period, the mammalian
(mouse and human) counterparts of Durga RNA were identified by scanning the 5'terminus of
the Kalirn gene. In mice, a number of lncRNAs are expressed from this genomic region. A couple
of RNAs that show considerable spatio-temporal overlap in expression with mouse Kalirn.
Mutational analyses of zebrafish durga RNA was also carried out. Truncated mutant RNA
corresponding to different parts of Durga were in vitro transcribed and injected into single cell
embryos to identify the minimal region necessary for its inductive effect on Kalirn expression.
Recently, it has been shown that some apparently non-coding RNAs may harbour tiny ORFs that
give rise to active peptides. Searching for such microORFs, two potential peptides that may arise
from Durga lncRNA were identified. However, flag tagged versions of these ORFs were
insufficient to trigger Kalirn over-expression. Although this is insufficient to establish that these
peptides are not expressed in vivo, current results indicate that the peptide is not required for
induction of Kalirn. Further, a mutant form of Durga RNA carrying mutations in the peptide
coding region, also induced Kalirn.

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