Feng Lifang, Wang Guangying, Hamilton Eileen P, Xiong Jie, Yan Guanxiong, Chen Kai, Chen Xiao, Dui Wen, Plemens Amber, Khadr Lara, Dhanekula Arjune, Juma Mina, Dang Hung Quang, Kapler Geoffrey M, Orias Eduardo, Miao Wei, Liu Yifan
Department of Pathology, University of Michigan, Ann Arbor, MI 48109, USA.
Key Laboratory of Aquatic Biodiversity and Conservation, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan 430072, China.
Nucleic Acids Res. 2017 Sep 19;45(16):9481-9502. doi: 10.1093/nar/gkx652.
Developmentally programmed genome rearrangement accompanies differentiation of the silent germline micronucleus into the transcriptionally active somatic macronucleus in the ciliated protozoan Tetrahymena thermophila. Internal eliminated sequences (IES) are excised, followed by rejoining of MAC-destined sequences, while fragmentation occurs at conserved chromosome breakage sequences, generating macronuclear chromosomes. Some macronuclear chromosomes, referred to as non-maintained chromosomes (NMC), are lost soon after differentiation. Large NMC contain genes implicated in development-specific roles. One such gene encodes the domesticated piggyBac transposase TPB6, required for heterochromatin-dependent precise excision of IES residing within exons of functionally important genes. These conserved exonic IES determine alternative transcription products in the developing macronucleus; some even contain free-standing genes. Examples of precise loss of some exonic IES in the micronucleus and retention of others in the macronucleus of related species suggest an evolutionary analogy to introns. Our results reveal that germline-limited sequences can encode genes with specific expression patterns and development-related functions, which may be a recurring theme in eukaryotic organisms experiencing programmed genome rearrangement during germline to soma differentiation.
在嗜热四膜虫中，发育程序控制的基因组重排伴随着沉默的生殖系微核分化为转录活跃的体细胞大核。内部消除序列（IES）被切除，随后是与大核相关序列的重新连接，而在保守的染色体断裂序列处发生片段化，从而产生大核染色体。一些大核染色体，称为非维持染色体（NMC），在分化后不久就会丢失。大型NMC包含与发育特异性作用相关的基因。其中一个这样的基因编码驯化的piggyBac转座酶TPB6，它是功能重要基因外显子内IES的异染色质依赖性精确切除所必需的。这些保守的外显子IES决定了发育中的大核中的替代转录产物；有些甚至包含独立的基因。相关物种微核中一些外显子IES的精确丢失和大核中其他外显子IES的保留的例子表明与内含子存在进化上的相似性。我们的结果表明，生殖系限制序列可以编码具有特定表达模式和发育相关功能的基因，这可能是在从生殖系到体细胞分化过程中经历程序性基因组重排的真核生物中的一个反复出现的主题。
