Parent-of-origin effects on nuclear chromatin organization and behavior in Drosophila model of Williams-Beuren Syndrome.. Parent-of-origin effects on nuclear chromatin organization and behavior in Drosophila model of Williams-Beuren Syndrome.

Development of prognostic models for neuropsychiatric disorders requires careful consideration of individual 1) parent-of-origin effects (POEs) relying on 2) nuclear 3D chromatin architecture of the nerve cells and 3) epigenetic impact of miRNAs produced in parental germ cells. The interplay of these events in shaping cognitive phenotypes in progeny is far from clear. Simple experimental model systems such as Drosophila can help to probe the causes and consequences leading to human neuropathology. Recently, we have developed a Drosophila model for Williams-Beuren Syndrome (WBS) – a mutant agnts3 of the agnostic locus (X:11AB) harboring limk1 gene for the key enzyme of actin remodeling LIM-kinase1. The mutation agnts3 drastically increases frequency of ectopic contacts (FEC) in specific regions of intercalary heterochromatin, suppresses learning acquisition and memory formation and affects locomotion. This study reveals that in reciprocal hybrids between agnts3 and the wild type strain Berlin the polytene chromosome bands are heterogeneous in manner of FEC regulation depending either on maternal or paternal gene origin. Bioinformatic analysis demonstrates that FEC between X:11AB and the other bands of the X chromosome partly depends on short (~ 30 bp) identical DNA fragments homologous to Drosophila 372 bp satellite DNA repeats. Although learning acquisition in conditioned courtship suppression paradigm is similar in hybrids, the middle-term memory formation shows patroclinic inheritance. Seemingly, this depends on changes in miR-974 expression levels. Several parameters of locomotion demonstrate heterosis. Our data indicate that agnts3 locus is capable of trans-regulating gene activity via POEs on chromatin nuclear organization, thereby affecting behavioral quantitative traits. Overall design: Deep-sequencing of small RNA of wild-type and Agnts3 flies and their hybrids.

神经精神疾病预后模型的开发，需审慎考量三类关键因素：1）亲本起源效应（parent-of-origin effects, POEs），其依托于神经细胞的细胞核三维染色质架构（nuclear 3D chromatin architecture）；2）亲本生殖细胞所产生的微小RNA（microRNAs, miRNAs）介导的表观遗传调控效应。上述三类事件在子代认知表型塑造过程中的相互作用机制，目前仍未完全阐明。

诸如果蝇（Drosophila）在内的简易实验模型系统，可为探究人类神经病理学的致病机制与病理结局提供研究载体。近期，我们构建了威廉姆斯-比尔伦综合征（Williams-Beuren Syndrome, WBS）的果蝇模型：该模型为agnostic基因座（X:11AB）的agnts3突变体，携带有编码肌动蛋白重塑关键酶LIM激酶1（LIM-kinase1）的limk1基因。agnts3突变可显著升高间期异染色质（intercalary heterochromatin）特定区域的异位接触频率（frequency of ectopic contacts, FEC），同时抑制学习获取与记忆形成过程，并对运动能力产生影响。

本研究发现，在agnts3突变体与野生型柏林品系（wild type strain Berlin）构建的正反交杂种中，多线染色体带区对异位接触频率的调控模式存在异质性，且该异质性取决于等位基因的亲本起源（母系或父系）。生物信息学分析显示，X染色体上X:11AB区域与其他染色体带区之间的异位接触，部分依赖于与果蝇372 bp卫星DNA重复序列同源的长度约30 bp的同源DNA片段。尽管正反交杂种在条件化求偶抑制范式（conditioned courtship suppression paradigm）下的学习获取能力无显著差异，但其中期记忆形成呈现父本倾向性遗传模式，该现象似乎与miR-974的表达水平变化相关。多项运动能力参数呈现杂种优势（heterosis）现象。

本研究数据表明，agnts3基因座可通过亲本起源效应（POEs）调控染色质的核组织架构，进而实现对基因活性的反式调控，最终影响行为数量性状。实验整体设计：对野生型、agnts3突变型果蝇及其正反交杂种的小RNA进行深度测序（deep-sequencing）。