Expression and distribution of synaptotagmin family members in the zebrafish retina

Abstract

Synaptotagmins belong to a large family of proteins. Although various synaptotagmins have been implicated as Ca2+ sensors for vesicle replenishment and release at conventional synapses, their roles at retinal ribbon synapses remain incompletely understood. Zebrafish is a widely used experimental model for retinal research. We therefore investigated the homology between human, rat, mouse, and zebrafish synaptotagmins 1–10 using a bioinformatics approach. We also characterized the expression and distribution of various synaptotagmin (syt) genes in the zebrafish retina using RT‐PCR, qPCR, and in situhybridization, focusing on the family members whose products likely underlie Ca2+‐dependent exocytosis in the central nervous system (synaptotagmins 1, 2, 5, and 7). Most zebrafish synaptotagmins are well conserved and can be grouped in the same classes as mammalian synaptotagmins, based on crucial amino acid residues needed for coordinating Ca2+ binding and determining phospholipid binding affinity. The only exception is synaptotagmin 1b, which lacks 34 amino acid residues in the C2B domain and is therefore unlikely to bind Ca2+ there. Additionally, the products of zebrafish syt5a and syt5b genes share identity with mammalian class 1 and 5 synaptotagmins. Zebrafish syt1, syt2, syt5, and syt7 paralogues are found in the zebrafish brain, eye, and retina, excepting syt1b, which is only present in the brain. The complementary expression pattern of the remaining paralogues in the retina suggests that syt1a and syt5a may underlie synchronous release and syt7a and syt7b may mediate asynchronous release or other Ca2+‐dependent processes in different retinal neurons.

Synaptotagmin-9 In Mouse Retina

“…Nothing is known about possible roles of Syt9 in retina. Consistent with evidence for Syt9 genes in zebrafish retina (Henry et al, 2022), we show evidence for Syt9 in multiple retinal neurons. Selective elimination of Syt9 from rods caused a reduction in scotopic b-waves and oscillatory potentials, while global elimination of Syt9 increased b-waves, suggesting actions at multiple sites in the retina.…”

A single base pair substitution in zebrafish distinguishes between innate and acute startle behavior regulation

“…Structurally, synaptotagmin proteins are composed of a transmembrane region, a linker region, and two calcium domains (C2A and C2B). In zebrafish, exon 2 of syt7a encodes a transmembrane domain and the last four exons encode two calcium binding domains, C2A and C2B ( Fig 2A ) [ 28 ]. In other vertebrates, the synaptotagmin 7 genes encodes multiple splicing isoforms, with at least three isoforms present in mouse and in humans [ 29 ].…”

“…In other vertebrates, the synaptotagmin 7 genes encodes multiple splicing isoforms, with at least three isoforms present in mouse and in humans [ 29 ]. Two alternatively spliced syt7a isoforms are predicted in zebrafish and expression of both has been confirmed within the zebrafish retina [ 28 ]. We named the isoforms syt7aα and syt7aβ , consistent with the nomenclature of syt7a isoforms present in mice ( Fig 2B ).…”

“…Across various species, including mice, birds, and zebrafish, syt7 is expressed ubiquitously and is enriched in the brain. Specifically, syt7 is expressed in auditory hair cells and the retina and moreover, syt7 knockout mice exhibit changes in auditory pre-pulse inhibition and anxiety-like behaviors, suggesting a potential role for syt7 in acoustically and/or visually-evoked behaviors [28,[30][31][32]. To test whether syt7a regulates auditory or visually evoked behaviors in zebrafish, we subjected syt7a 34bpdel (p432) mutants to previously validated behavioral paradigms including the visuomotor response [33], the dark flash response [34,35], the light flash response [35], and the acoustic startle response [24,36].…”

A single base pair substitution on Chromosome 25 in zebrafish distinguishes between development and acute regulation of behavioral thresholds

“…Structurally, synaptotagmin proteins are composed of a transmembrane region, a linker region, and two calcium domains (C2A and C2B). In zebrafish, exon 2 of syt7a encodes a transmembrane domain and the last four exons encode two calcium binding domains, C2A and C2B (Figure 2A) (28). In other vertebrates, the synaptotagmin 7 genes encodes multiple splicing isoforms, with at least three isoforms present in mouse and in humans (29).…”