Restricted expression ofreggiegenes and proteins during early zebrafish development

Abstract

Reggies are plasma membrane-associated proteins and characteristic markers of lipidraft microdomains. They are highly conserved from flies to humans and have been implicated in axon regeneration and cell process and contact formation, possibly providing functional platforms for cell-signaling in neurons and other cell types. We analyzed reggie mRNA and protein expression patterns during early zebrafish development. All three zebrafish genes, re-1a, -2a, and -2b, span a considerably diverse set of expression patterns, and their proteins are induced maternally, showing ubiquitous expression at early stages. Although re-2a mRNA can be observed in differentiating neurons in the brain, spinal cord, and neurogenic placodes, re-2b is transcribed mainly in head mesoderm, in neural crest derivates, and along somite boundaries. re-1a mRNA is present at high levels in expression domains that overlap with the combined expression pattern of both re-2 genes except at the somites, where it complements the pattern of re-2b. Immunostaining on embryos reveals reggie protein localization at the cell membrane, at cell-cell contacts, and along all early axon tracts. The early phase of reggie expression suggests a basic and ubiquitous function during the first stages of embryogenesis and into the gastrula period. Upon segmentation, a second phase of expression shows distinctly localized expression patterns, indicating tissue-specific roles and an involvement of re-1a/re-2a in neural development.

Scaffolding microdomains and beyond: the function of reggie/flotillin proteins

“…Reggie-1a is highly expressed in domains overlapping with the expression pattern of both reggie-2 genes, except at the somites where it complements the pattern of reggie2b. Immunostainings using reggie antibodies stain all fiber tracts in the developing nervous system [52], indicating involvement of reggie-1a and -2a in neuronal differentiation as expected, due to their identification in regenerating axons. Morpholino knock-down of reggie expression in the developing zebrafish leads to severe morphological defects starting early during gastrulation.…”

“…Due to genome duplication in fish, there are two copies of each reggie gene in zebrafish [7], but one reggie-1 gene was rendered non-functional during evolution. In good correlation to the ubiquitous expression in stable cell lines, reggie-1a, reggie-2a and -2b are expressed ubiquitously during the early stages of zebrafish development [52]. Upon segmentation, the expression pattern becomes more restricted.…”

“…Misexpression of reggie-1 and -2 in the eye imaginal disc leads to severe mistargeting of specific cell-adhesion molecules of the immunglobulin superfamily (IgCAMs), resulting in an irregular ommatidial pattern. Similarly, misexpression in the wing imaginal disc leads to extension of the wingless signal and disrupts normal wing development [M. Hoehne, There are no comprehensive studies on the expression of reggies in adult organisms, but reggie-1 is apparently widely expressed in many different tissues, with particularly high expression in brain, while reggie-2 expression is slightly more restricted [5,32,52]. In summary, reggie expression seems to be essential for all cells in culture and during early stages of development.…”

Function of Flotillins in Receptor Tyrosine Kinase Signaling and Endocytosis: Role of Tyrosine Phosphorylation and Oligomerization

“…Their original discovery as "reggies" suggested a function in neuronal regeneration in the goldfish (2,45), which has been later verified by further studies from the same group (57,60,61). However, the regenerative capacity of the optic nerve is poorly conserved in mammals, making a generalization of the regenerative function of flotillins in the nervous system of mammals difficult.…”

Ancient origin of reggie (flotillin), reggie-like, and other lipid-raft proteins: convergent evolution of the SPFH domain

“…17,18]. Reggies/flotillins are highly expressed in virtually all growing structures of the developing zebrafish, particularly in tissues actively undergoing rapid proliferation and differentiation [19]. Moreover, morpholino knockdown in zebrafish embryos [Málaga-Trillo E., RiveraMilla E. and Stuermer C. A. O., unpublished data], as well as overexpression experiments in fruitflies [20] bring about striking morphological phenotypes that include cytoskeleton rearrangements, indicating an important requirement for reggies/flotillins during early signaling pathways.…”