Not all Notch pathway mutations are equal in the embryonic mouse retina

Area of Science:

• Developmental biology
• Neuroscience
• Genetics

Background:

• Notch signaling is crucial for vertebrate retinal progenitor cell fate determination, involving complex interactions between ligands, receptors, and ternary complex components that regulate Hes effector gene activity.
• Multiple paralogues of Notch signaling components exist in vertebrates, often acting redundantly or compensatorily during development, complicating pathway dissection.

Approach:

• Utilized seven germline or conditional mutant mice and two spatiotemporally distinct Cre drivers to perturb the Notch ternary complex and Hes genes.
• Investigated the requirement of Notch signaling in the optic stalk/nerve head for sustained Hes1 expression and activity.
• Assessed the functional redundancy of Hes1, Hes3, and Hes5 genes during early retinal histogenesis.

Key Points:

• Disrupting Notch signaling consistently inhibited mitotic growth and led to an overproduction of ganglion cells in the retina.
• Identified that sustained Hes1 expression in the optic stalk/nerve head is regulated independently of Notch signaling.
• Demonstrated that during photoreceptor genesis, Rbpj and Hes1 have both Notch-dependent and -independent roles that exert opposing effects on photoreceptor development.

Conclusions:

• Notch signaling plays a critical role in regulating retinal progenitor cell proliferation and differentiation, with specific roles identified in the optic stalk and during photoreceptor development.
• Hes1 regulation is partially independent of Notch signaling in the optic stalk, highlighting pathway complexity.
• Functional redundancy and opposing roles of key genes like Rbpj and Hes1 underscore the intricate regulatory network governing retinal histogenesis.