Abstract
Endocytosis is a multi-step process involving a large number of proteins, both general factors, such as clathrin and adaptor protein complexes, and unique proteins, which modulate specialized endocytic processes, like the EHD proteins. EHDs are a family of Eps15 Homology Domain containing proteins that consists of four mammalian homologs, one C. elegans, one Drosophila melanogaster and two plants orthologs. These membrane-associated proteins are involved in different steps of endocytic trafficking pathways. We have previously shown that the Drosophila EHD ortholog, PAST1, associates predominantly with the plasma membrane. Mutations in Past1 result in defects in endocytosis, male sterility, temperature sensitivity and premature death of the flies. Also, Past1 genetically interacts with Notch. In the present study, we investigated the role of PAST1 in the developing fly eye. In mutant flies lacking PAST1, abnormal differentiation of photoreceptors R1, R6 and R7 was evident, with partial penetrance. Likewise, five cone cells were present instead of four. Expression of transgenic PAST1 resulted in a dominant negative effect, with a phenotype similar to that of the deletion mutant, and appearance of additional inter-ommatidial pigment cells. Our results strongly suggest a role for PAST1 in differentiation of photoreceptors R1/R6/R7 and cone cells of the fly ommatidia.
Highlights
Drosophila PAST1 is an endocytic protein, which belongs to the family of Eps15 homology (EH) domain-containing proteins
To examine the possibility that PAST1 plays a role during eye development in Drosophila, we explored the effect of a null Past1 mutation
No external morphological defects were detected by scanning electron microscopy in the eyes of three-days-old adults homozygous for a null Past1 mutation compared to wild type flies (Fig 1C)
Summary
Drosophila PAST1 is an endocytic protein, which belongs to the family of Eps homology (EH) domain-containing proteins. The Past gene encodes two transcripts, RNA-A and RNA-B. The corresponding proteins, PAST1A and PAST1B, differ in seven amino acids missing from the N-terminus of PAST1B [1]. The two Past transcripts are differentially expressed both temporally and spatially during the life cycle of the fly [2]. Past1B is expressed throughout development in both males and females, while Past1A is only expressed from the third larval stage onwards, and is restricted to the male testes [2]. Past null mutant flies, generated by imprecise excision of a P-element, reach adulthood, but are temperature sensitive, infertile and die precociously. As expected, these flies present a defect in endocytosis.
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