bantam Is Required for Optic Lobe Development and Glial Cell Proliferation

microRNAs (miRNAs) are small, conserved, non-coding RNAs that contribute to the control of many different cellular processes, including cell fate specification and growth control. Drosophila bantam, a conserved miRNA, is involved in several functions, such as stimulating proliferation and inhibiting apoptosis in the wing disc. Here, we reported the detailed expression pattern of bantam in the developing optic lobe, and demonstrated a new, essential role in promoting proliferation of mitotic cells in the optic lobe, including stem cells and differentiated glial cells. Changes in bantam levels autonomously affected glial cell number and distribution, and non-autonomously affected photoreceptor neuron axon projection patterns. Furthermore, we showed that bantam promotes the proliferation of mitotically active glial cells and affects their distribution, largely through down regulation of the T-box transcription factor, optomotor-blind (omb, Flybase, bifid). Expression of omb can rescue the bantam phenotype, and restore the normal glial cell number and proper glial cell positioning in most Drosophila brains. These results suggest that bantam is critical for maintaining the stem cell pools in the outer proliferation center and glial precursor cell regions of the optic lobe, and that its expression in glial cells is crucial for their proliferation and distribution.

微小RNA（microRNAs，简称miRNAs）是一类小型保守非编码RNA，参与调控诸多不同的细胞过程，包括细胞命运特化与生长调控。果蝇（Drosophila）bantam作为一种保守miRNA，参与多项生理功能，例如在翅盘（wing disc）中刺激细胞增殖并抑制细胞凋亡。本研究详细报道了bantam在发育视叶（optic lobe）中的表达模式，并证实其在视叶有丝分裂细胞（包括干细胞与分化神经胶质细胞）的增殖促进中发挥了全新的关键作用。bantam表达水平的改变可自主性地影响胶质细胞的数量与分布，同时非自主性地影响感光神经元轴突投射模式。进一步研究表明，bantam主要通过下调T盒转录因子（T-box transcription factor）运动视觉盲（optomotor-blind，简称omb，Flybase数据库编号bifid），促进有丝分裂活性胶质细胞的增殖并调控其分布。omb的表达可挽救bantam所致的表型异常，并在多数果蝇大脑中恢复正常的胶质细胞数量与正确的胶质细胞定位。上述结果提示，bantam对于维持视叶外部增殖中心与胶质前体细胞区域的干细胞库至关重要，且其在胶质细胞中的表达对于胶质细胞的增殖与分布亦具有关键意义。