αβ-tubulin heterodimers: Origins and regulation of microtubule building blocks

αβ-tubulin is an essential protein that is found in all eukaryotic cells. αβ-tubulins assemble into microtubule polymers that form intracellular transport networks, mitotic and meiotic spindles, and protrusive structures, including cilia and axons. Building these specialized structures creates a demand for αβ-tubulin that can vary across cell type, developmental timing, and cell cycle stage. In this review, we discuss how αβ-tubulins likely emerged from monomeric ancestors into gene families with multiple isotypes and regulatory mechanisms that meet cellular demands for αβ-tubulin. This emergence is accompanied by pathways that regulate the biogenesis and recycling of αβ-tubulin to build networks rapidly and maintain them across long timescales. We propose that the layers of regulation from αβ-tubulin gene copy number, gene sequence elements, mRNA degradation, and protein biogenesis/recycling pathways comprise an integrated program for nimble and robust response to cellular demand for αβ-tubulin. Exploring the cellular signals that control this program and program innovations across species are important next steps for the field.