Autophagy is a self-catabolic process through which cellular components are delivered to lysosomes for degradation. There are three types of autophagy, i.e., macroautophagy, chaperone-mediated autophagy (CMA), and microautophagy. In macroautophagy, a portion of the cytoplasm is wrapped by the autophagosome, which then fuses with lysosomes and delivers the engulfed cytoplasm for degradation. In CMA, the translocation of cytosolic substrates to the lysosomal lumen is directly across the limiting membrane of lysosomes. In microautophagy, lytic organelles, including endosomes or lysosomes, take up a portion of the cytoplasm directly. Although macroautophagy has been investigated extensively, microautophagy has received much less attention. Nonetheless, it has become evident that microautophagy plays a variety of cellular roles from yeast to mammals. Here we review the very recent updates of microautophagy. In particular, we focus on the feature of the degradative substrates and the molecular machinery that mediates microautophagy.

自噬是一种自我分解代谢过程，通过该过程，细胞成分被递送至溶酶体进行降解。自噬可分为三种类型，即巨自噬、分子伴侣介导的自噬（CMA）和微自噬。在巨自噬中，一部分细胞质被自噬体包裹，然后与溶酶体融合并递送被吞噬的细胞质进行降解。在 CMA 中，胞质底物直接穿过溶酶体的限制膜易位至溶酶体腔。在微自噬中，裂解细胞器，包括内体或溶酶体，直接占据细胞质的一部分。尽管巨自噬已被广泛研究，但微自噬受到的关注却少得多。尽管如此，很明显微自噬在从酵母到哺乳动物的多种细胞中发挥着作用。在这里，我们回顾一下微自噬的最新进展。我们特别关注降解底物的特征和介导微自噬的分子机制。