Abstract
ABSTRACTEarly embryogenesis requires tightly controlled temporal and spatial coordination of cellular behavior and signaling. Modulations are achieved at multiple levels, from cellular transcription to tissue-scale behavior. Intracellularly, the endolysosomal system emerges as an important regulator at different levels, but in vivo studies are rare. In the frog Xenopus, little is known about the developmental roles of endosomal regulators, or their potential involvement in signaling, especially for late endosomes. Here, we analyzed a hypothesized role of Rab7 in this context, a small GTPase known for its role as a late endosomal regulator. First, rab7 showed strong maternal expression. Following localized zygotic transcript enrichment in the mesodermal ring and neural plate, it was found in tailbud-stage neural ectoderm, notochord, pronephros, eyes and neural crest tissues. Inhibition resulted in strong axis defects caused by a requirement of rab7 for mesodermal patterning and correct gastrulation movements. To test a potential involvement in growth factor signaling, we analyzed early Wnt-dependent processes in the mesoderm. Our results suggest a selective requirement for ligand-induced Wnt activation, implicating a context-dependent role of Rab7.
Highlights
Embryonic processes like germ layer formation, induction of body axes, gastrulation, neural induction and tissue differentiation require tight control of cellular processes, including temporal and spatial activation of specific sets of signaling pathways
Strong maternal expression was found in the animal half of cleavage stages, a signal detected until the onset of zygotic transcription after midblastula transition (MBT) (Fig. 1A,B; Fig. S1A)
Stronger signals were detected in the neural plate ectoderm and in the axial, notochordal mesoderm, latter of which continued to be positive for rab7 during neurulation
Summary
Embryonic processes like germ layer formation, induction of body axes, gastrulation, neural induction and tissue differentiation require tight control of cellular processes, including temporal and spatial activation of specific sets of signaling pathways. Regulation of endocytosis or membrane trafficking can control activation, intensity, or duration of signal transduction following receptor activation (Sigismund et al, 2012). This has only been analyzed in few developmental processes in vivo, as altering basic cellular processes can have dramatic effects. Endocytosis of membrane receptors is considered a way of downregulation of signaling. Receptor complexes can be inactivated and recycled back to the plasma membrane. They are retained in EE membranes while these organelles mature into
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