Scripting a place in time

Abstract

Evidence in many experimental systems supports the idea that non-uniform distributions of morphogen proteins encode positional information in developing tissues. There is also strong evidence that morphogen dispersal is mediated by cytonemes and that morphogen proteins transfer from producing to receiving cells at morphogenetic synapses that form at sites of cytoneme contacts. This essay considers some implications of this mechanism and its relevance to various contexts including large single cells such as the pre-cellular Drosophila embryo and the ciliate Stentor.

Keywords: Bicoid; Cytoneme; Gene expression; Gradient; Morphogen.

Figure 1. Krüppel RNA expression and Bicoid protein in the pre-cellular Drosophila embryo

Nascent Krüppel RNA was detected by in situ hybridization in several cycle 7 nuclei and in many more cycle 9 nuclei, all centered at the approximate midpoint along the anterior-posterior axis. Bicoid protein was detected by antibody staining in a concentration gradient and concentrated in nuclei at the indicated nuclear cycles. The nuclei do not reach the embryo cortex until nuclear cycle 9. From Ali-Murthy and Kornberg, 2016

Figure 2. Patterned structures in Stentor

A drawing of Stentor depicts several patterned features; the fluorescence micrograph shows structures stained with anti-tubulin antibody (Slabodnick et al., 2014).