Small and large intestine express a truncated Dab1 isoform that assembles in cell-cell junctions and co-localizes with proteins involved in endocytosis

Autophagy markers expression pattern in developing liver of the yotari (dab1-/-) mice and humans

Autophagy plays an important role in the physiology and pathology of the liver. Several negative autophagy regulators have been discovered, including epidermal growth factor receptor (EGFR), mediated by activation of the PI3K/Akt/mTOR signaling pathway. Disabled-1 (Dab1) is one of the mediating adaptor factors of PI3K/Akt/mTOR signaling pathways. We investigated the potential impact of Dab1 on autophagy-related markers (LC3B, LAMP2A, HSC70, and GRP78) in the developing liver by using a model of yotari mice and compared it with autophagy marker expression in human liver development. Mouse embryos were obtained at gestation days 13.5 and 15.5 (E13.5 and E15.5), and a total of 5 normal human conceptuses were obtained between gestation days 5 and 10. Histological sections were analyzed by immunohistochemistry. The highest expression of the early endosome-forming factor LC3B and the microautophagy factor LAMP2a was observed at the transition from embryonic to early fetal phase, whereas the expression of the chaperones HSC 70 and GRP78 was highest at embryonic phase. The expression patterns of three of these factors in mouse liver were different from those in human liver: the expression of LC3B was high at E13.5, that of HSC 70 at 15.5, whereas the expression of GRP78 did not change significantly. On the other hand, the expression pattern of LAMP2a was similar to that in human development and was higher at E15.5 than at E13.5. Moreover, knockout of Dab1 resulted in significantly lower expression of LC3B and LAMP2a in mouse embryo livers (at E13.5), indicating a possible role of Dab1 in regulating autophagy during embryonic development in the liver.

Disabled 1 Is Part of a Signaling Pathway Activated by Epidermal Growth Factor Receptor

Disabled 1 (Dab1) is an adapter protein for very low density lipoprotein receptor (VLDLR) and apolipoprotein E receptor 2 (ApoER2) and an integral component of the Reelin pathway which orchestrates neuronal layering during embryonic brain development. Activation of Dab1 is induced by binding of Reelin to ApoER2 and VLDLR and phosphorylation of Dab1 mediated by Src family kinases. Here we show that Dab1 also acts as an adaptor for epidermal growth factor receptor (EGFR) and can be phosphorylated by epidermal growth factor (EGF) binding to EGFR. Phosphorylation of Dab1 depends on the kinase activity of EGFR constituting a signal pathway independent of Reelin and its receptors.

Expression and localization of DAB1 and Reelin during normal human kidney development

Aim

To explore the spatial and temporal expression patterns of DAB1 and Reelin in the developing and postnatal healthy human kidneys as potential determinants of kidney development.

Methods

Paraffin-embedded fetal kidney tissue between the 13/14th and 38th developmental weeks (dw) and postnatal tissue at 1.5 and 7 years were stained with DAB1 and Reelin antibodies by double immunofluorescence.

Results

During the fetal kidney development and postnatal period, DAB1 and Reelin showed specific spatial expression pattern and diverse fluorescence intensity. During the fetal period, DAB1 was strongly expressed in the distal convoluted tubules (DCT), with strong reactivity, and diversely in the proximal convoluted tubules (PCT) and glomeruli. In the postnatal period, DAB1 expression decreased. The strongest Reelin expression in early fetal stages was observed in the PCT. In the postnatal period, Reelin expression decreased dramatically in all observed structures. These two markers were colocalized during early developmental stages, mostly in PCT, DCT, and podocytes.

Conclusion

The appearance of DAB1 and Reelin during fetal kidney development confirms their potential significant role in the formation of kidney structure or function. High DAB1 expression in the DCT implies its regulatory role in tubular formation or function maintenance during development. Reelin was highly expressed in human kidneys at early fetal stages, mostly in the PCT, while at later fetal stages and postnatal period its expression decreased.