The Blimp-1 transcription factor acts in non-neuronal cells to regulate terminal differentiation of the Drosophila eye.

The formation of a functional organ such as the eye requires specification of the correct cell types and their terminal differentiation into cells with the appropriate morphologies and functions. Here, we show that the zinc-finger transcription factor Blimp-1 acts in secondary and tertiary pigment cells in the Drosophila retina to promote the formation of a bi-convex corneal lens with normal refractive power, and in cone cells to enable complete extension of the photoreceptor rhabdomeres. Blimp-1 expression depends on the hormone ecdysone, and loss of ecdysone signaling causes similar differentiation defects. Timely termination of Blimp-1 expression is also important, as its overexpression in the eye has deleterious effects. Our transcriptomic analysis revealed that Blimp-1 regulates the expression of many structural and secreted proteins in the retina. Blimp-1 may function in part by repressing another transcription factor; Slow border cells is highly upregulated in the absence of Blimp-1, and its overexpression reproduces many of the effects of removing Blimp-1. This work provides insight into the transcriptional networks and cellular interactions that produce the structures necessary for visual function.

An apposition compound eye adapted for nocturnal vision in the moth midge Clogmia albipunctata (Williston) (Diptera: Psychodidae).

Morphology and anatomy, dark/light adaptational changes and optics of the compound eyes of the nocturnal moth midge Clogmia albipunctata (Williston) are studied. Its apposition type of eye consists of approximately 260 well-separated ommatidia. Each ommatidium features a biconvex corneal lens covered by corneal nipples measuring around 17nm in height; a crystalline cone of the acone type; and an open (laterally fused) rhabdom formed by eight retinular cells (R1-R8). The corneal lens, whose biological significance is addressed, is composed of a thick yellow-coloured inner lens unit (ILU) surrounded by a thin, colourless outer lens unit (OLU). We identified two types of ommatidia: dorsally located T-type ommatidia and ventrally located P-type ommatidia. In the T-type ommatidia, the rhabdomeres of the retinular cells R7 and R8 are centrally located and are arranged in tandem with R7 above R8. In comparison, in the P-type ommatidia, only the R8 rhabdomere is central, whereas the R7 rhabdomere locates in the peripheral ring. Above the distal tip of the rhabdom, the crystalline cone and the PPCs form an aperture that dynamically changes its size under dark/light conditions, thus modulating the amount of light that reaches the photoreceptive layer. The Clogmia albipunctata eye has a low F-number of 1.2, a high interommatidial angle of 11° and a large eye parameter of 4.6µm·rad. The eye is characterized by relatively poor spatial resolution, but exhibits high absolute sensitivity.

Quantitative characterization of adhesion and stiffness of corneal lens of Drosophila melanogaster using atomic force microscopy.

Atomic force Microscopy (AFM) has become a versatile tool in biology due to its advantage of high-resolution imaging of biological samples close to their native condition. Apart from imaging, AFM can also measure the local mechanical properties of the surfaces. In this study, we explore the possibility of using AFM to quantify the rough eye phenotype of Drosophila melanogaster through mechanical properties. We have measured adhesion force, stiffness and elastic modulus of the corneal lens using AFM. Various parameters affecting these measurements like cantilever stiffness and tip geometry are systematically studied and the measurement procedures are standardized. Results show that the mean adhesion force of the ommatidial surface varies from 36 nN to 16 nN based on the location. The mean stiffness is 483 ± 5 N/m, and the elastic modulus is 3.4 ± 0.05 GPa (95% confidence level) at the center of ommatidia. These properties are found to be different in corneal lens of eye expressing human mutant tau gene (mutant). The adhesion force, stiffness and elastic modulus are decreased in the mutant. We conclude that the measurement of surface and mechanical properties of D. melanogaster using AFM can be used for quantitative evaluation of 'rough eye' surface.