BLM-s，BCL-2家族的一員，之新穎功能發現：參與憂鬱以及焦慮情緒的調控

Abstract

BLM-s是BCL-2家族成員中的一員，大量存在於發育中大腦皮質的postmitotic neurons，具有可以誘導細胞進行凋亡(apoptosis)的功能。我們利用同源重組的方式已經製備出Blm-s的基因剃除小鼠(knockout mice)。基因剔除鼠在外觀以及健康上皆屬正常，且具有正常的生育能力，其子代皆嚴格遵守孟德爾遺傳定律(Mendelian heredity rule)。在各個主要器官中，不論是外觀或是組織型態，皆不會因為Blm-s基因的剃除而導致任何顯著上的異常。此外，我們發現BLM-s特別在杏仁核(amygdala)、海馬迴(hippocampus)以及內側前額葉皮層(medial prefrontal cortex)中的某些神經細胞中進行表現。由於這些腦區被認為參與記憶以及情緒的調控，因此我們首先針對這些基因剃除小鼠進行學習以及記憶行為的探討。在Morris水迷宫(Morris water maze)的試驗中，Blm-s基因剃除小鼠在空間學習以及記憶行為的表現上皆屬正常，然而卻在適應期時呈現不游動的異常表現。這樣的結果顯示了Blm-s基因的剃除，有可能導致小鼠在情緒的調控上表現異常。因此，我們更進一步進行其他與情緒調控相關的動物行為試驗，像是強迫游泳試驗(forced swimming test)、懸尾試驗(tail suspension test)、舉臂式十字迷宮試驗(elevated plus-maze test)以及曠野實驗(open field test)。其結果皆表明Blm-s基因剃除小鼠可能表現出憂鬱或焦慮的異常行為特徵。更進一步的研究顯示，這樣的一個行為表徵有可能是因為海馬迴神經的生成異常以及齒狀回(dentate gyrus)樹突棘(dendritic spine)的複雜度減少所導致。綜合上述實驗，我們的研究結果發現BLM-s具有其他非細胞凋亡(non-apoptotic)的新功能，尤其是在調控情緒以及壓力有關的神經迴路 (neurocircuitry)，其細胞/分子的訊息傳遞以及生成中扮演著相當重要的一個角色。

Blm-s (Bcl-2-like molecule, short form) is one of the Bcl-2 family member. It abounds in postmitotic neurons of the developing cerebral cortex and functions as a BH3-only apoptosis sensitizer/derepressor to mediate apoptosis of the immature migratory postmitotic neurons. We have generated conventional Blm-s knockout mice through genomic homologous recombination strategy. These Blm-s-KO mice have normal outlook, appear healthy and live to the expected life. They also show normal fertility and the genotype of their descendants strictly follow the autosomal Mendelian heredity rule. There is no obvious abnormality in their internal organ grossly. Microscopically, we found BLM-s is expressed in layer V of the medial prefrontal cortex (mPFC), hippocampus, and in some subsets of neurons in amygdala, which disappears in Blm-s-KO mice. Since these brain regions are involved in memory and emotional regulation, we investigate the memory and learning behaviors of Blm-s-KO mice. Blm-s-KO mice show normal spatial learning and memory performance by Morris water maze (MWM) test, but they exhibit poorer mobility in adaption period. These results suggest that the Blm-s-KO have emotional changes. Thus, we performed forced swimming test (FST), tail suspension test (TST), elevated plus maze (EPM) and open field test (OFT) to demonstrate that Blm-s-KO mice indeed exhibit depression and/or anxiety behaviors. Moreover, further study demonstrates that decreased hippocampal adult neurogenesis and decreased dendritic spine complexity possibly contribute to these behavioral phenotypes observed in Blm-s-KO mice. Collectively, our results uncover a novel non-apoptotic function of BLM-s and reveal that BLM-s might play an important role in the regulation of developmental or cellular/molecular processes of neurocircuitry involved in emotional or stress control.