The cytoskeleton is a dynamic protein scaffold that regulates many crucial cytosolic processes in animal cells. Actin, intermediate filaments, and microtubules (MTs) are the three main networks of the cytoskeleton, and the dynamic changes and coordination between these polymer proteins are important for biological functions such as cell migration, cell division, and cell shape maintenance. A large number of proteins have been identified as facilitating the proper regulation of cytoskeletal networks. However, many questions are still waiting to be answered, such as how are the dynamics of each filament regulated in detail? How do these cytoskeletal networks coordinate with each other to perform complicated cellular functions?Plus-end tracking proteins (+TIPs) are a group of proteins that accumulate at the growing ends of MTs to regulate their dynamics. Over the past 20 years, many +TIPs have been found, and their roles have been studied. However, it is still unclear how +TIPs collaborate with each other to facilitate the growth of MTs. In addition, studies over the past decade have also found that +TIPs play a role in regulating the crosstalk between MTs and actin, and it has become clear that many biological processes are controlled by this crosstalk. In this dissertation, I will discuss my two key findings and the hypotheses that were drawn from them: (1) A major +TIP called CLIP-170 can induce biomolecular condensate containing other members of +TIP network, which leads to the hypothesis that biomolecular condensates play a role in promoting MT polymerization. (2) CLIP-170 binds directly to actin, and this interaction competes for binding to MTs, which leads to the hypothesis that CLIP-170 may mediate actin-MT crosstalk through the direct binding to actin.The first major question addressed in this thesis is how do +TIPs regulate MT dynamics through +TIP:+TIP interactions. +TIPs interact with each other to form a network through many weak multivalent interactions, hereafter called the +TIP network. My work investigates the possibility that the +TIP network is not just regulatory network, but a physical network, one that forms a phase-separated structure known as a liquid droplet at the MT plus-end. Previously, the Goodson lab proposed that the +TIP network serves as a physical scaffold to constrain the fragile MT end, thereby promoting MT polymerization and so acting like a polymerization chaperone. The recent explosion of work on liquid droplets suggested to us that the proposed physical scaffold might actually be a liquid droplet. It is difficult to test this hypothesis directly because the small and dynamic nature of the endogenous +TIP "comets" makes it hard to study them through microscope-based techniques. Therefore, I used superstructures induced by CLIP-170 overexpression (previously called "patches") as a tool to gain insight into the endogenous +TIP network because CLIP-170 patches are larger, contain other members of the +TIP network, and have the potential to reflect the physiological +TIP networks.To test this hypothesis that CLIP-170 patches are biomolecular condensates, we performed experiments to determine whether CLIP-170 patches have the established hallmarks of a biomolecular condensate. The four common features used to identify biomolecular condensates are: a) elastic deformability of the structures, b) ability to undergo fusion and fission, c) selectivity to include certain biomolecules while excluding others, and d) rapid protein exchange between the droplets and the surrounding environment such as cytoplasm. Our results from experiments including video microscopy, immunofluorescence staining, and Fluorescence Recovery After Photobleaching (FRAP) show that CLIP-170-induced patches do have the four hallmarks found in other biomolecular condensates. Furthermore, our bioinformatic studies showed that CLIP-170 and other +TIPs have sequence features common to biomolecular condensates, i.e. multiple protein binding sites and intrinsically disordered regions. These sequence features are conserved evolutionarily, which implies functionally significant roles for these regions. Taken together, our results demonstrate that CLIP-170 patches are biomolecular condensates and raise the possibility that the +TIP network may form biomolecular condensates at MT plus ends. We suggest that these condensates serve as a polymerization chaperone to promote MT polymerization.The second major question addressed by this thesis is the potential role of the +TIP CLIP-170 in crosstalk between the actin and MT cytoskeletons. Previously, the Goodson lab proposed the hypothesis that the +TIP EB1 binds directly to actin at actin-rich cortex regions to absorb EB1 from MT plus end onto actin, thereby reducing the stability of MTs. It is established that CLIP-170 binds directly to EB1, and that CLIP-170 requires the presence of EB1 to track MT plus ends in cells. This close relationship between EB1 and CLIP-170 made us wonder whether CLIP-170 can also regulate actin-MT crosstalk through a similar mechanism as previously proposed for EB1. Using high-speed cosedimentation assays, we found that CLIP-170 binds directly to actin. In addition, together with CLIP-170 fragments and mutants, I found that the CLIP-170 actin binding surface overlaps with the MT binding surface. My competition assays further demonstrate that the CLIP-170:actin interactions compete with the CLIP-170:MT interactions. Although we did not see obvious CLIP-170 colocalization with actin in cells, my bioinformatic studies suggest that CLIP-170 actin-binding sites are well-conserved throughout a wide-range of species, which implies a functional significance. Taken together, our results lead us to propose that actin and MTs may compete for binding with CLIP-170 in actin-rich regions to destabilize MTs in these regions, similar to the mechanism previously hypothesized in EB1.In summary, my work in this dissertation has enhanced our understanding of the roles of the +TIPs in regulating MT dynamics and actin-MT crosstalk. We have shown that the so-called "patches" induced by CLIP-170 overexpression are biomolecular condensates. This conclusion leads us to propose that the endogenous +TIP network at the ends of MTs is also a biomolecular condensate, and so could be considered a type of membraneless organelle. These ideas are consistent with the previous work from the Goodson lab suggesting that that the +TIP network promotes MT growth through its network of physical interactions. We have also determined that actin and MTs compete with each other for direct binding to CLIP-170, and we hypothesize that this CLIP-170:actin interaction may help control MT dynamics at actin-rich sites in cells.