Slit refers collectively to a family of related genes which encode a corresponding set of secreted proteins, also collectively referred to as Slit. Slit proteins act as midline repellents, preventing the crossing of longitudinal axons through the midline of the central nervous system

Central nervous system

The central nervous system is the part of the nervous system that integrates the information that it receives from, and coordinates the activity of, all parts of the bodies of bilaterian animals—that is, all multicellular animals except sponges and radially symmetric animals such as jellyfish...

 of most bilaterian animal species, including mice

Mouse

A mouse is a small mammal belonging to the order of rodents. The best known mouse species is the common house mouse . It is also a popular pet. In some places, certain kinds of field mice are also common. This rodent is eaten by large birds such as hawks and eagles...

, chicken

Chicken

The chicken is a domesticated fowl, a subspecies of the Red Junglefowl. As one of the most common and widespread domestic animals, and with a population of more than 24 billion in 2003, there are more chickens in the world than any other species of bird...

s, human

Human

Humans are the only living species in the Homo genus...

s, insect

Insect

Insects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae...

s, nematode

Nematode

The nematodes or roundworms are the most diverse phylum of pseudocoelomates, and one of the most diverse of all animals. Nematode species are very difficult to distinguish; over 28,000 have been described, of which over 16,000 are parasitic. It has been estimated that the total number of nematode...

 worms and planarians. It also prevents the recrossing of commissural axons. Its canonical receptor is Robo

Roundabout (gene)

Roundabout is the gene for the Roundabout receptor. There is a family of Robo transmembrane receptors and they are the canonical receptors for the signaling molecule Slit, although there may be more Slit receptors besides Robo...

 but it may have other receptors. The Slit protein is produced and secreted by cells within the floor plate

Floor plate

The floor plate is a structure integral to the developing nervous system of vertebrate organisms. Located on the ventral midline of the embryonic neural tube, the floor plate is a specialized glial structure that spans the anteroposterior axis from the midbrain to the tail regions...

 (in vertebrates) or by midline glia (in insects) and diffuses outward. Slit/Robo signaling is important in pioneer axon

Pioneer axon

Pioneer axon is an axon that lays down initial growing path for the axons of other neurons to follow.-References:; covered in...

guidance. Humans, mice and other vertebrates possess three Slit genes, known as Slit1, Slit2, and Slit3, which cooperate to mediate midline repulsion. Other animals, such as insects and nematode worms, possess a single Slit gene.