What is the netlike array of protein filaments that maintains the shape of the nucleus called?

The netlike array of protein filaments that maintains the shape of the nucleus is known as the nuclear lamina. This structure is located just inside the inner membrane of the nuclear envelope and is primarily composed of intermediate filament proteins, particularly lamins. The nuclear lamina provides mechanical support to the nucleus, helping to maintain its shape and also plays a critical role in organizing the chromatin within the nucleus and anchoring it to the nuclear envelope.

The other choices represent different biological structures: the cellulose layer is a component of plant cell walls, the cytoskeleton refers to a network of protein filaments that provides structure and shape to the entire cell, and chromatin is the complex of DNA and proteins found in the nucleus that packages and protects the genetic material. Each of these has distinct functions that do not pertain to the specific support structure of the nucleus itself, which is why the nuclear lamina is the correct choice for this question.