Establishing a growth axis in fucoid algae.

Recent studies indicate that fucoid zygotes establish developmental polarity much earlier than previously thought. A growth axis is first set in place at fertilization, with the site of sperm entry defining the rhizoid pole of the axis. This initial axis is a default axis, which is only used as the final growth axis if the zygote fails to detect spatial cues (such as sunlight) in its intertidal environment. However, the zygote usually senses vectorial information; it then abandons the sperm-induced axis and assembles a new axis de novo in accordance with the perceived vector(s).