Abstract
Understanding the control of stem cell (SC) differentiation is important to comprehend developmental processes as well as to develop clinical applications. Lin28 is a conserved molecule that is involved in SC maintenance and differentiation by regulating let-7 miRNA maturation. However, little is known about the in vivo function of Lin28. Here, we report critical roles for lin-28 during oogenesis. We found that let-7 maturation was increased in lin-28 null mutant fly ovaries. We showed that lin-28 null mutant female flies displayed reduced fecundity, due to defects in egg chamber formation. More specifically, we demonstrated that in mutant ovaries, the egg chambers fuse during early oogenesis resulting in abnormal late egg chambers. We also showed that this phenotype is the combined result of impaired germline SC differentiation and follicle SC differentiation. We suggest a model in which these multiple oogenesis defects result from a misregulation of the ecdysone signaling network, through the fine-tuning of Abrupt and Fasciclin2 expression. Our results give a better understanding of the evolutionarily conserved role of lin-28 on GSC maintenance and differentiation.
Highlights
The Cold-Shock Domain (CSD) protein Lin28 was initially identified in Caenorhabditis elegans (C. elegans) as a component of the heterochronic pathway that regulates the timing of cell fate specification [1]
For instance the dorsal internal oblique muscles (DIOMs), muscles which are required for eclosion and which are lost within 12 hours after eclosion, they are maintained during adulthood upon let-7 deletion [23]
We suggest that a potential network involving Lin-28/let-7/Ecdysone signaling/Abrupt/Fas2 is needed during germline stem cell (GSC) differentiation and border cell (BC) migration (Figure 10B)
Summary
The Cold-Shock Domain (CSD) protein Lin was initially identified in Caenorhabditis elegans (C. elegans) as a component of the heterochronic pathway that regulates the timing of cell fate specification [1]. Lin inhibits let-7 processing [5]. Lin protein interacts with the let-7 precursor (pre-let-7), resulting in inhibition of let-7 maturation [6]. The let-7 inhibition occurs through the physical interaction of the pre-let-7 loop and Lin protein, preventing further processing of pre-let-7 towards the mature form of let-7 [7,8]. Together, these interactions create a feedback loop between Lin and let-7, leading to a strict regulation of let-7 maturation [9]
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