Hunchback (gene)

Hunchback is a maternal effect and zygotic gene expressed in the embryos of the fruit fly Drosophila melanogaster. In maternal effect genes, the RNA or protein from the mother's gene is deposited into the oocyte or embryo before the embryo can express its own zygotic genes.

Hunchback is a morphogen, meaning the concentration gradient of Hunchback at a specific region determines the segment or body part it develops into. This is possible because Hunchback is a transcription factor protein that binds to genes' regulatory regions, changing RNA expression levels.

Hunchback expression pathway

Maternal Hunchback RNA enters the embryo at the syncytial blastoderm stage, where the entire embryo has undergone many nuclear divisions but has one communal cytoplasm, allowing for RNA to disperse freely throughout the embryo. This allows the maternal effect genes Hunchback, Bicoid, Nanos, and Caudal to regulate zygotic genes to create different identities for different regions of the body.

The first step is establishing the anterior and posterior regions, which later give rise to the respective head and abdomen. In the syncytial blastoderm, Bicoid and Nanos RNA bind to protein ropes involved in cellular locomotion and intracellular transport called microtubules that ferry the RNA to the anterior and posterior regions, respectively. Hunchback does not bind to microtubules and therefore diffuses uniformly throughout the embryo. However, Nanos represses the translation of the Hunchback protein.