A natural antisense transcript regulates Zeb2/Sip1 gene expression during Snail1-induced epithelial-mesenchymal transition

Genomic landscape of developing male germ cells

Spermatogenesis is a highly orchestrated developmental process by which spermatogonia develop into mature spermatozoa. This process involves many testis- or male germ cell-specific gene products whose expressions are strictly regulated. In the past decade the advent of high-throughput gene expression analytical techniques has made functional genomic studies of this process, particularly in model animals such as mice and rats, feasible and practical. These studies have just begun to reveal the complexity of the genomic landscape of the developing male germ cells. Over 50% of the mouse and rat genome are expressed during testicular development. Among transcripts present in germ cells, 40% - 60% are uncharacterized. A number of genes, and consequently their associated biological pathways, are differentially expressed at different stages of spermatogenesis. Developing male germ cells present a rich repertoire of genetic processes. Tissue-specific as well as spermatogenesis stage-specific alternative splicing of genes exemplifies the complexity of genome expression. In addition to this layer of control, discoveries of abundant presence of antisense transcripts, expressed psuedogenes, non-coding RNAs (ncRNA) including long ncRNAs, microRNAs (miRNAs) and Piwi-interacting RNAs (piRNAs), and retrogenes all point to the presence of multiple layers of expression and functional regulation in male germ cells. It is anticipated that application of systems biology approaches will further our understanding of the regulatory mechanism of spermatogenesis.

Transcriptional regulation of cell polarity in EMT and cancer

The epithelial-to-mesenchymal transition (EMT) is a crucial process in tumour progression providing tumour cells with the ability to escape from the primary tumour, to migrate to distant regions and to invade tissues. EMT requires a loss of cell-cell adhesion and apical-basal polarity, as well as the acquisition of a fibroblastoid motile phenotype. Several transcription factors have emerged in recent years that induce EMT, with important implications for tumour progression. However, their effects on cell polarity remain unclear. Here, we have re-examined the data available related to the effect of EMT related transcription factors on epithelial cell plasticity, focusing on their impact on cell polarity. Transcriptional and post-transcriptional regulatory mechanisms mediated by several inducers of EMT, in particular the ZEB and Snail factors, downregulate the expression and/or functional organization of core polarity complexes. We also summarize data on the expression of cell polarity genes in human tumours and analyse genetic interactions that highlight the existence of complex regulatory networks converging on the regulation of cell polarity by EMT inducers in human breast carcinomas. These recent observations provide new insights into the relationship between alterations in cell polarity components and EMT in cancer, opening new avenues for their potential use as therapeutic targets to prevent tumour progression.

From cells to organs: building polarized tissue

How do animal cells assemble into tissues and organs? A diverse array of tissue structures and shapes can be formed by organizing groups of cells into different polarized arrangements and by coordinating their polarity in space and time. Conserved design principles underlying this diversity are emerging from studies of model organisms and tissues. We discuss how conserved polarity complexes, signalling networks, transcription factors, membrane-trafficking pathways, mechanisms for forming lumens in tubes and other hollow structures, and transitions between different types of polarity, such as between epithelial and mesenchymal cells, are used in similar and iterative manners to build all tissues.

Noncoding RNA in development

Non-protein-coding sequences increasingly dominate the genomes of multicellular organisms as their complexity increases, in contrast to protein-coding genes, which remain relatively static. Most of the mammalian genome and indeed that of all eukaryotes is expressed in a cell- and tissue-specific manner, and there is mounting evidence that much of this transcription is involved in the regulation of differentiation and development. Different classes of small and large noncoding RNAs (ncRNAs) have been shown to regulate almost every level of gene expression, including the activation and repression of homeotic genes and the targeting of chromatin-remodeling complexes. ncRNAs are involved in developmental processes in both simple and complex eukaryotes, and we illustrate this in the latter by focusing on the animal germline, brain, and eye. While most have yet to be systematically studied, the emerging evidence suggests that there is a vast hidden layer of regulatory ncRNAs that constitutes the majority of the genomic programming of multicellular organisms and plays a major role in controlling the epigenetic trajectories that underlie their ontogeny.

Non-coding RNAs take centre stage in epithelial-to-mesenchymal transition

Noncoding RNAs are emerging as central players in gene expression regulation through the targeting of a plethora of mRNAs. Several recent papers report on the regulation of the epithelial phenotype by the miR-200 (200 family of miRNAs) family and a natural antisense transcript, both acting on the E-cadherin repressors zinc-finger E-box-binding homeobox factors ZEB1 and ZEB2. These findings open new avenues for understanding the modulation of the epithelial-to-mesenchymal transition in physiological and pathological situations.

Nkx2.2 antisense RNA overexpression enhanced oligodendrocytic differentiation

Nkx2.2AS is an endogenous antisense transcript to Nkx2.2 gene, subcellularly located in the cytoplasm. We tested if Nkx2.2AS transcripts have any biological function by regulating transcription level of Nkx2.2 coding gene in the differentiation of neural stem cells. Forced expression of Nkx2.2AS in neural stem cells enhanced induction of differentiation along lineage of oligodendrocytes. Further analyses showed that overexpression of Nkx2.2AS induced modest increase in Nkx2.2 mRNA level, suggesting that the upregulation of Nkx2.2 mRNA level can be a minor cause of enhanced induction of oligodendrocytic differentiation by Nkx2.2AS overexpression. These results together imply that Nkx2.2AS has a certain biological function which is likely to be not only based on the affect on transcription level of Nkx2.2 coding gene in cis, but also on the other mechanisms.