The X-linked methyl binding protein gene Kaiso is highly expressed in brain but is not mutated in Rett syndrome patients

Mapping the Neural Substrates of Recent and Remote Visual Imprinting Memory in the Chick Brain

Social attachment formed by filial imprinting in newborn chicks undergoes a process of memory consolidation that involves rearrangement of its neural storage substrates. In the first 3 h after imprinting it depends on the integrity of the intermediate medial mesopallium (IMM) and beyond that time on unidentified memory storage structures dubbed S’. To search for the S’ memory system in the chick brain, we mapped and compared patterns of activity induced by retrieval of filial attachment memory before and after this critical transition. Chicks were trained in the visual imprinting task, and their memory was reactivated by imprinting stimulus either 1 h (recent memory retrieval) or 24 h (remote memory retrieval) after the completion of training. Patterns of brain activity were mapped by in situ hybridization to mRNA of an immediate early gene c-fos. We also mapped c-fos expression induced by the first presentation of the imprinting stimulus. Memory retrieval triggered massive c-fos expression in the chick brain both 1 and 24 h after the end of training. These activity patterns mostly coincided with the c-fos expression induced by the first presentation of imprinting stimulus. However, in the hippocampus c-fos induction was observed only after the first exposure to imprinting stimulus but not after memory retrieval. In the IMM, medio-rostral nidopallium/mesopallium, and hyperpallium densocellulare c-fos activation was induced by retrieval of only the remote but not of the recent memory. These c-fos mapping data point to the candidate brain structures for systems reorganization of imprinting memory in chicks.

Distribution of Kaiso protein in mouse tissues

The Kaiso protein was originally described as a BTB/POZ zinc-finger transcription factor and a p120-catenin-binding partner. It is a DNA methylation-dependent transcriptional repressor, but its biological role in mice is still unknown. Here, we characterized a Kaiso-specific antibody by examining Kaiso protein distribution by immunofluorescence microscopy in the following tissues and cell types of adult mice: skin, small intestine, mammary glands, urinary bladder, and others. This study is the first to demonstrate that Kaiso is expressed in most of the examined tissues. Kaiso was localized to the nucleus in almost all tissues. However, it was primarily cytoplasmic in photoreceptor cells in the eye (rods and cones). Furthermore, Kaiso is expressed in a specific subset of male germ cells that are characterized by partly positive PLZF and Bmi-1 staining. In this study, we present the first confirmation of the reliability of expression data using Kaiso knockout mice.

Donor splice-site mutation in CUL4B is likely cause of X-linked intellectual disability

X-linked intellectual disability is the most common form of cognitive disability in males. Syndromic intellectual disability encompasses cognitive deficits with other medical and behavioral manifestations. Recently, a large family with a novel form of syndromic X-linked intellectual disability was characterized. Eight of 24 members of the family are male and had cognitive dysfunction, short stature, aphasia, skeletal abnormalities, and minor anomalies. To identify the causative gene(s), we performed exome sequencing in three affected boys, both parents, and an unaffected sister. We identified a haplotype consisting of eight variants located in cis within the linkage region that segregated with affected members in the family. Of these variants, two were novel. The first was at the splice-donor site of intron 7 (c.974+1G>T) in the cullin-RING ubiquitin ligase (E3) gene, CUL4B. This variant is predicted to result in failure to splice and remove intron 7 from the primary transcript. The second variant mapped to the 3'-UTR region of the KAISO gene (c.1127T>G). Sanger sequencing validated the variants in these relatives as well as in three affected males and five carriers. The KAISO gene variant was predicted to create a binding site for the microRNAs miR-4999 and miR-4774; however, luciferase expression assays failed to validate increased targeting of these miRNAs to the variant 3'-UTR. This SNP may affect 3'-UTR structure leading to decreased mRNA stability. Our results suggest that the intellectual disability phenotype in this family is caused by aberrant splicing and removal of intron 7 from CUL4B gene primary transcript.

Epigenetic mechanisms in the development and maintenance of dopaminergic neurons

Mesodiencephalic dopaminergic (mdDA) neurons are located in the ventral mesodiencephalon and are involved in psychiatric disorders and severely affected in neurodegenerative diseases such as Parkinson's disease. mdDA neuronal development has received much attention in the last 15 years and many transcription factors involved in mdDA specification have been discovered. More recently however, the impact of epigenetic regulation has come into focus, and it's emerging that the processes of histone modification and DNA methylation form the basis of genetic switches that operate during mdDA development. Here, we review the epigenetic control of mdDA development, maturation and maintenance. As we highlight, epigenetic mechanisms play a pivotal role in all of these processes and the knowledge gathered from studying epigenetics in these contexts may aid our understanding of mdDA-related pathologies.

CpG methylation in neurons: message, memory, or mask?

The study of CpG methylation of genomic DNA in neurons has emerged from the shadow of cancer biology into a fundamental investigation of neuronal physiology. This advance began with the discovery that catalytic and receptor proteins related to the insertion and recognition of this chemical mark are robustly expressed in neurons. At the smallest scale of analysis is the methylation of a single cytosine base within a regulatory cognate sequence. This singular alteration in a nucleotide can profoundly modify transcription factor binding with a consequent effect on the primary 'transcript'. At the single promoter level, the methylation-demethylation of CpG islands and associated alterations in local chromatin assemblies creates a type of cellular 'memory' capable of long-term regulation of transcription particularly in stages of brain development, differentiation, and maturation. Finally, at the genome-wide scale, methylation studies from post-mortem brains suggest that CpG methylation may serve to cap the genome into active and inactive territories introducing a 'masking' function. This may facilitate rapid DNA-protein interactions by ambient transcriptional proteins onto actively networked gene promoters. Beyond this broad portrayal, there are vast gaps in our understanding of the pathway between neuronal activity and CpG methylation. These include the regulation in post-mitotic neurons of the executor proteins, such as the DNA methyltransferases, the elusive and putative demethylases, and the interactions with histone modifying enzymes.

The methyl-CpG binding proteins Mecp2, Mbd2 and Kaiso are dispensable for mouse embryogenesis, but play a redundant function in neural differentiation

Background

The precise molecular changes that occur when a neural stem (NS) cell switches from a programme of self-renewal to commit towards a specific lineage are not currently well understood. However it is clear that control of gene expression plays an important role in this process. DNA methylation, a mark of transcriptionally silent chromatin, has similarly been shown to play important roles in neural cell fate commitment in vivo. While DNA methylation is known to play important roles in neural specification during embryonic development, no such role has been shown for any of the methyl-CpG binding proteins (Mecps) in mice.

Methodology/Principal Findings

To explore the role of DNA methylation in neural cell fate decisions, we have investigated the function of Mecps in mouse development and in neural stem cell derivation, maintenance, and differentiation. In order to test whether the absence of phenotype in singly-mutant animals could be due to functional redundancy between Mecps, we created mice and neural stem cells simultaneously lacking Mecp2, Mbd2 and Zbtb33. No evidence for functional redundancy between these genes in embryonic development or in the derivation or maintenance of neural stem cells in culture was detectable. However evidence for a defect in neuronal commitment of triple knockout NS cells was found.

Conclusions/Significance

Although DNA methylation is indispensable for mammalian embryonic development, we show that simultaneous deficiency of three methyl-CpG binding proteins genes is compatible with apparently normal mouse embryogenesis. Nevertheless, we provide genetic evidence for redundancy of function between methyl-CpG binding proteins in postnatal mice.