Characterization of the AP-1 µ1A and µ1B adaptins in zebrafish (Danio rerio).

ABSTRACT

Protein transport between the trans-Golgi network and endosomes is mediated by transport vesicles formed by the adaptor-protein complex AP-1, consisting of the adaptins γ1, ß1, µ1, σ1. Mammalia express µ1A ubiquitously and isoform µ1B in polarized epithelia. Mouse γ1 or µ1A 'knock out's revealed that AP-1 is indispensable for embryonic development. We isolated µ1A and µ1B from Danio rerio. Analysis of µ1A and µ1B expression revealed tissue-specific expression for either one during embryogenesis and in adult tissues in contrast to their expression in mammalia. µ1B transcript was detected in organs of endodermal derivation and "knock-down" experiments gave rise to embryos defective in formation of intestine, liver, and pronephric ducts. Development ceased at 7-8 dpf. µ1B is not expressed in murine liver, indicating loss of µ1B expression and establishment of alternative sorting mechanisms during mammalian development.