Cis-acting Control of Human Developmental Regulator GLI2

Abstract

Gene regulation is a highly complex process and involves the coordination of RNA polymerase, enhancers and promoters, multiple transcription factors, silencers, insulators, and locus control regions. The spatiotemporal activity of a gene requires the presence of intact coding sequences as well as properly functioning cis-acting regulatory control. The identification and functional characterization of cis-acting elements is one of the greatest challenges of the post-genomic era for better understanding of the language, syntax and grammar that is encoded in regulatory DNA. Gene expression plays a significant role in the evolution of vertebrate complexity and diversity during development. The vertebrate GLI family (gliomaassociated oncogene family members 1, 2, and 3) of transcription factors are key transducers of one such pathway known as Sonic hedgehog (Shh) signaling. Shh-Gli interactions have been extensively scrutinized from last couple of decades by genetic, molecular and biochemical means. In the present study, an important mediator of Shh signaling, GLI2 gene was focused. GLI2 has been implicated in diverse set of embryonic developmental processes including patterning and growth of the central nervous system, craniofacial structures, skeleton, limb, skin, and internal organs. In addition, a number of clinical conditions and developmental defects have already been associated with mutation in this key developmental regulator. Precise spatio-temporal expression of Gli2 is critical for the proper specification of these structures in vertebrates. In this study, I identified and characterized, the cis-regulatory catalogue of human GLI2 gene Results & Conclusions Towards the elucidation of genetic mechanisms, by which the transcription of GLI2 genes is regulated during early embryonic development, deep evolutionary constraints (tetrapod-teleost) have been used as an indicator to pinpoint the conserved intronic intervals of human GLI2 gene. This ancient catalogue act as tissue-specific enhancers in transient transgenic zebrafish assays and induce reporter gene expression in a diverse set of embryonic domains, where GLI2 is known to be expressed endogenously. Interestingly, these GLI2-associated enhancers have considerable overlapping expression territories during zebrafish development. Significance Elucidation of the GLI2-associated cis-regulatory network offers a novel perspective for better understanding the genetic mechanisms by which the downstream effectors of Hh signaling cascade might be regulated during embryogenesis. In addition, these cis-regulatory modules are strong candidates for mutational studies of GLI2-associated human birth defects, which cannot be attributed to any exonic mutation.