Drosophila R8 photoreceptor cell subtype specification requires hibris

Abstract

Cell differentiation and cell fate determination in sensory systems are essential for stimulus discrimination and coding of environmental stimuli. Color vision is based on the differential color sensitivity of retinal photoreceptors, however the developmental programs that control photoreceptor cell differentiation and specify color sensitivity are poorly understood. In Drosophila melanogaster, there is evidence that the color sensitivity of different photoreceptors in the compound eye is regulated by inductive signals between cells, but the exact nature of these signals and how they are propagated remains unknown. We conducted a genetic screen to identify additional regulators of this process and identified a novel mutation in the hibris gene, which encodes an irre cell recognition module protein (IRM). These immunoglobulin super family cell adhesion molecules include human KIRREL and nephrin (NPHS1). hibris is expressed dynamically in the developing Drosophila melanogaster eye and loss-of-function mutations give rise to a diverse range of mutant phenotypes including disruption of the specification of R8 photoreceptor cell diversity. We demonstrate that hibris is required within the retina, and that hibris over-expression is sufficient to disrupt normal photoreceptor cell patterning. These findings suggest an additional layer of complexity in the signaling process that produces paired expression of opsin genes in adjacent R7 and R8 photoreceptor cells.

Functional opsin patterning for Drosophila color vision is established through signaling pathways in adjacent object-detection neurons

“…In addition, Activin and BMP signaling are required upstream of the Hippo pathway to establish expression of Rh5 or Rh6 in R8 ( Wells et al, 2017 ). Involvement of Epidermal growth factor receptor, Rhomboid and Hibris is also reported ( Birkholz et al, 2009a , b ; Tan et al, 2020 ). However, mechanisms by which the instructive Rh5-inducing signal is transmitted from R7 to R8 remains unknown.…”

Functional opsin patterning forDrosophilacolor vision is established through signaling pathways in adjacent object-detection neurons

“…In addition, Activin and BMP signaling are required upstream of the Hippo pathway to establish expression of Rh5 or Rh6 in R8 (Wells et al, 2017). Involvement of Epidermal growth factor receptor, Rhomboid, and Hibris is also reported (Birkholz et al, 2009a; Birkholz et al, 2009b; Tan et al, 2020). However, mechanisms by which the instructive signal is transmitted from R7 to R8 remains unknown.…”

Insect opsins and evo-devo: what have we learned in 25 years?

“…Atonal increases Senseless expression, inhibiting Rough, leading to R8 cell fate (figure 1 b ). The cell-adhesion protein Hibris is also involved in signalling for proper R8 specification [26]. R2 and R5 are specified next, where Rough is highly expressed and represses Senseless leading to R2 and R5 cell fate.…”