Cadieux Benoît, Chitramuthu Babykumari P, Baranowski David, Bennett Hugh P J
Endocrine Laboratory, Royal Victoria Hospital, McGill University Health Centre, Montreal, Quebec, Canada.
BMC Genomics. 2005 Nov 8;6:156. doi: 10.1186/1471-2164-6-156.
Progranulin is an epithelial tissue growth factor (also known as proepithelin, acrogranin and PC-cell-derived growth factor) that has been implicated in development, wound healing and in the progression of many cancers. The single mammalian progranulin gene encodes a glycoprotein precursor consisting of seven and one half tandemly repeated non-identical copies of the cystine-rich granulin motif. A genome-wide duplication event hypothesized to have occurred at the base of the teleost radiation predicts that mammalian progranulin may be represented by two co-orthologues in zebrafish.
The cDNAs encoding two zebrafish granulin precursors, progranulins-A and -B, were characterized and found to contain 10 and 9 copies of the granulin motif respectively. The cDNAs and genes encoding the two forms of granulin, progranulins-1 and -2, were also cloned and sequenced. Both latter peptides were found to be encoded by precursors with a simplified architecture consisting of one and one half copies of the granulin motif. A cDNA encoding a chimeric progranulin which likely arises through the mechanism of trans-splicing between grn1 and grn2 was also characterized. A non-coding RNA gene with antisense complementarity to both grn1 and grn2 was identified which may have functional implications with respect to gene dosage, as well as in restricting the formation of the chimeric form of progranulin. Chromosomal localization of the four progranulin (grn) genes reveals syntenic conservation for grna only, suggesting that it is the true orthologue of mammalian grn. RT-PCR and whole-mount in situ hybridization analysis of zebrafish grns during development reveals that combined expression of grna and grnb, but not grn1 and grn2, recapitulate many of the expression patterns observed for the murine counterpart. This includes maternal deposition, widespread central nervous system distribution and specific localization within the epithelial compartments of various organs.
In support of the duplication-degeneration-complementation model of duplicate gene retention, partitioning of expression between grna and grnb was observed in the intermediate cell mass and yolk syncytial layer, respectively. Taken together these expression patterns suggest that the function of an ancestral grn gene has been devolved upon four paralogues in zebrafish.
颗粒蛋白前体是一种上皮组织生长因子（也称为前上皮素、肢端颗粒蛋白和PC细胞衍生生长因子），与发育、伤口愈合以及多种癌症的进展有关。单个哺乳动物颗粒蛋白前体基因编码一种糖蛋白前体，该前体由富含胱氨酸的颗粒蛋白基序的七个半串联重复的不同拷贝组成。据推测，在硬骨鱼辐射基部发生的全基因组复制事件预示着哺乳动物颗粒蛋白前体在斑马鱼中可能由两个共直系同源物代表。
对编码两种斑马鱼颗粒蛋白前体（颗粒蛋白-A和颗粒蛋白-B）的cDNA进行了表征，发现它们分别包含10个和9个颗粒蛋白基序拷贝。还克隆并测序了编码两种颗粒蛋白形式（颗粒蛋白-1和颗粒蛋白-2）的cDNA和基因。发现后两种肽均由具有简化结构的前体编码，该结构由一个半颗粒蛋白基序拷贝组成。还对一个可能通过grn1和grn2之间的反式剪接机制产生的嵌合颗粒蛋白前体的cDNA进行了表征。鉴定出一个与grn1和grn2均具有反义互补性的非编码RNA基因，这可能对基因剂量以及限制嵌合形式颗粒蛋白前体的形成具有功能意义。四个颗粒蛋白（grn）基因的染色体定位显示仅grna存在同线保守性，这表明它是哺乳动物grn的真正直系同源物。对斑马鱼grn在发育过程中的RT-PCR和整体原位杂交分析表明，grna和grnb的联合表达（而非grn1和grn2）概括了小鼠对应物中观察到的许多表达模式。这包括母体沉积、广泛的中枢神经系统分布以及在各种器官的上皮区室中的特定定位。
为支持重复基因保留的复制-退化-互补模型，在中间细胞团和卵黄合胞体层中分别观察到了grna和grnb之间的表达分配。综合这些表达模式表明，斑马鱼中一个祖先grn基因的功能已分散到四个旁系同源物上。
