IMPC:Characterisation of 4933427D14Rik, an Lhx1 regulated gene, and specification of the left-right body axis

从外部看，人类和其他哺乳动物都是两侧对称的。然而在内部它们表现出不变的左右不对称。例如，心脏向左倾斜，而肝脏位于腹部的右侧。这种不对称是如何形成的，在生物学和医学上都引起了极大的兴趣。人类左-右（L-R）模式形成的缺陷会导致影响心脏、脉管系统、肺部和胃肠道的出生缺陷，可能危及生命。为了了解这些L-R轴缺陷是如何发展的，更充分地了解L-R模式建立的分子和细胞机制是很重要的。纤毛是重要的细胞器，可以有感觉或运动的作用，在建立L-R轴是至关重要的。纤毛类似于细胞表面膜上的毛发状突起，纤毛内部是微管细胞骨架。纤毛起源于中心体，中心体是一种细胞器，是微管的主要组织中心，由母中心粒和子中心粒组成。纤毛的形成称为纤毛发生，当母中心粒停靠在形成纤毛基底的膜上，纤毛的微管细胞骨架由此延伸而出。在哺乳动物的早期发育中，形成了一种短暂的、结构上独特的结构，即节点，它对建立L-R轴至关重要。在形态学上，淋巴结由一窝细胞组成，每个细胞都有一根活动的纤毛。纤毛的刻板旋转产生了液体从右向左流过淋巴结的单向流动，导致包括Nodal在内的少数基因的不对称表达。不对称节点信号对于确定L-R体轴至关重要，因为节点信号的扰动会导致L-R轴模式的缺陷。Lhx1是一种同源盒结构域转录因子，其表达依赖于节点信号。胚胎缺乏Lhx1显示，在大量的缺陷中，节点形态发生缺陷和正确的L-R轴模式。我们最近通过转录谱实验鉴定了Lhx1调控基因，其中有一个相对未被表征的基因4933427D14Rik。利用IMPC资源，我们的工作将确定4933427D14Rik在建立L-R轴的早期开发中所起的作用。初步研究表明，4933427D14Rik是一种中心粒卫星蛋白，可能在中心粒复制和纤毛发生中都起作用。4933427D14Rik突变体胚胎的初步表型分析揭示了胚胎发育中的问题，这些问题可归因于纤毛发生和L-R建立的缺陷。在医学上，最近发现4933427D14Rik在患有口腔-面部-手指综合征（OFDS）的纤毛病患者中发生突变，突出了该基因的重要性。因此，4933427D14Rik可能在Lhx1/Nodal信号下游的L-R轴的建立中发挥关键作用，该向心卫星蛋白的鉴定将最终为了解OFDS和相关人类出生缺陷的机制提供线索。

Externally humans, and other mammals, appear bilaterally symmetrical. However internally they display an invariant left-right asymmetry. For example, the heart is tilted towards the left while the liver is placed on the right side of the abdomen. How this asymmetry is established is of great interest, both biologically and medically. Defects in human left-right (L-R) pattern formation cause birth defects affecting the heart, vasculature, lungs and gastrointestinal tract that can be life threatening. To understand how these L-R axis defects develop, it is important to more fully understand the molecular and cellular mechanisms by which L-R patterning is established. Cilia are important cellular organelles that can have sensory or motile roles and are critical in setting up the L-R axis. Cilia resemble small hair-like projections on the surface membrane of the cell and inside the cilia is a microtubule-based cytoskeleton. Cilia originate from centrosomes, a cell organelle that serves as the main microtubule organising centre, and consists of a mother and a daughter centriole. The formation of cilia, termed ciliogenesis, initiates when the mother centriole docks at the membrane forming the basal body of the cilia and from which the microtubule cytoskeleton of the cilia extends. In early mammalian development, a transient and architecturally distinct structure, the node, is formed and is essential for establishing the L-R axis. Morphologically the node is formed of a pit of cells, with each cell possessing a motile cilium. Stereotyped rotation of the cilia generates a unidirectional flow of fluid across the node from right to left, leading to asymmetric expression of a handful of genes, including Nodal. Asymmetric Nodal signalling is essential for specifying the L-R body axis as perturbations in Nodal signalling can lead to defects in L-R axis patterning. Lhx1 is a homeobox domain transcription factor whose expression is dependent on Nodal signalling. Embryos lacking Lhx1 display, among a plethora of faults, defects in node morphogenesis and in correct L-R axis patterning. We have recently identified Lhx1 regulated genes through transcriptional profiling experiments, among which was a relatively uncharacterised gene 4933427D14Rik. Exploiting the IMPC resource, our work will establish the role 4933427D14Rik plays in early development in setting up the L-R axis. Preliminary studies suggest that 4933427D14Rik is a centriolar satellite protein that may function in both centriole duplication and ciliogenesis. Preliminary phenotyping of 4933427D14Rik mutant embryos revealed problems in embryonic development that can be attributed to defects in ciliogenesis and L-R establishment. Medically, the recent finding that 4933427D14Rik is mutated in a ciliopathy patient with oral-facial-digital syndrome (OFDS) highlights the importance of this gene. Hence, 4933427D14Rik may play a key role in setting up the L-R axis downstream of Lhx1/Nodal signalling and characterisation of this centriolar satellite protein will ultimately provide insight into the mechanism underlying OFDS and related human birth defects.