Citron Kinase 在斑馬魚胚胎發育中扮演的角色

Abstract

Citron kinase (CRIK)為一種可活化Rho 的下游的絲胺酸-羥丁胺酸激酶。過去的研究認為CRIK 在調節哺乳類動物的細胞質裂中扮演很重要的角色。例如，在CRIK 缺乏的小鼠中，會產生不正常的細胞質裂和神經發育而造成嚴重的癲癇並於三週內死亡，但其機制還不太了解。 我們以斑馬魚為模式動物來研究CRIK 在細胞質裂和其他生物反應過程中的作用。我們收集了從雙細胞到發育24 小時間不同發育程度的胚胎進行原位雜交，發現細胞分裂早期crik 廣泛分布在整個胚體，到了256 細胞期後則特別聚集在卵黃與胚體交接之空腔層(yolk syncytial layer, YSL)，到10 個體節時期crik 也表現在神經上。為進一步瞭解crik 在斑馬魚發育中的功能，我們設計了兩個MO，來抑制crik 的轉譯。經顯微注射的胚胎出現細胞分裂、外包的缺陷、甚至死亡，直接打入crik 的mRNA 即可部分減少這些缺陷，進一步證明crik 的缺乏會造成上述缺陷。更仔細觀察MO 處理過的胚胎，出現多核細胞的比例對照組高出許多，而總細胞數則相對的較少推測是不完全的細胞質裂造成的結果。另外，當我們直接將MO 顯微注射到YSL 時，造成的缺陷更為嚴重，且出現明顯外包行為的問題，進 而影響胚胎的原腸化。因此我們推論在早期斑馬魚胚胎發育時期，CRIK 特別表現在YSL 影響著細胞質裂和外包行為。

Citron kinase (CRIK) is a serine-threonine kinase and a Rho effector kinase. Previously, CRIK has been suggested to play a role in regulating cytokinesis in mammalian cells. CRIK depleting mice shows abnormal cytokinesis and defective neurogenesis, and then causes severe epilepsy and died in 3 weeks. The results suggest that CRIK is involved in cytokinesis, but the mechanism is not clear. To elucidate the actions of CRIK in cytokinesis and other biological processes, we used zebrafish as a model. In this study, we perform whole-mount in situ hybridization of series developmental stages of zebrafish embryos from two-cell stage to 24-hpf embryos to observe the temporal and spatial expression patterns of crik during embryogenesis. We found crik expressed ubiquitous in whole blastomere at early cleavage stages but specifically accumulate at the yolk syncytial layer (YSL) in the other early developmental stages after 256-cell stage and also expressed in neurons after 10-somite stage. To further study the function of crik in zebrafish development, we designed two translational blocking morpholino oligonucleotides (tMO) to knockdown crik expression and overexpress. The loss of function of crik resulted in dose-dependent defects, including cell division, epiboly defect and even embryonic death. The fact that those defect morphology was specifically induce by crik knockdown was strongly proved by the rescue experiment. The knockdown defect phenotype can be partially rescue by crik mRNA. Besides, stronger epiboly defect was observed when MOs were injected into YSL. We suggest that CRIK expressed in YSL and affected not only cytokinesis but also epiboly in early embryonic developmental stage in zebrafish.