Perinuclear theca

The perinuclear theca is a condensed cytosolic protein layer that surrounds the sperm nucleus, except in the neck region. It can be structurally and compositionally divided into the subacrosomal layer and the postacrosomal sheath, also known as the calyx. The subacrosomal layer is important for acrosome assembly and is continuous with the outer periacrosomal layer. The calyx has a role in sperm–egg interactions and egg activation during fertilization.

The perinuclear theca is a very thin, capsule-like layer surrounding the sperm nucleus. In the subcellular resource, staining of only the subacrosomal layer in the upper part of the sperm head has been annotated as perinuclear theca, while staining of the posterior postacrosomal layer close to the connecting piece has been annotated as calyx.

Read more about the perinuclear theca as a substructure of sperm.