**6. Homology of proteins of the NXF family and axonemal dyneins as a source of evolutionary relationship**

Searching for related proteins and aligning sequences using the multiple sequence alignment tool base has demonstrated that among the proteins that are homologous to the factor NXF1, axonemal dynein of various organisms—especially its light chain—is most frequent. Aligning sequences that exhibit homology demonstrates that the N-terminus of the Dm NXF1 protein, which includes RBD domains and the LRR (leucine-rich repeats), corresponds to the axonemal light chain of dynein in vertebrates (**Figure 6**). At the LRR site, there is a sequence that exhibits a high degree of homology (marked by bold typeface in **Figure 6**), both when comparing different NXF factors (orthologous and paralogous), and comparing the SBR protein with sequences of light chains of dynein (**Figure 6**). The functions of this sequence are yet to be determined.

The dynein complex is a multicomponent system consisting of light, light intermediate, intermediate, and heavy chains of dynein [72]. Interacting with a multitude of protein and ribonucleic partners, the LC8 and TcTex1 light chains of dynein enable a link between different forms of the transported cargo and heavy chains of dynein that function as molecular motors [73, 74]. By interacting with its partner dynacin complex, the dynein complex enables cytoplasmic transport of macromolecular complexes, vesicles, and organelles [75], including particles containing RNAs [74, 76].

**159**

apparatus of the cell.

**Figure 6.**

*1202072EGVYDYGWG).*

evolutionary conservative).

*Spermatogenesis in* Drosophila melanogaster: *Key Features and the Role of the NXF1…*

In the fruit fly, the null mutants of the genes that encode the light or heavy chain of dynein have anomalies of wings and bristles, exhibit male and female sterility, and are characterized by disrupted sensory axon trajectories [71], thus demonstrat-

*Results of the alignment of the amino acid sequences of LRR domains of different NXF factors, including SBR, and dynein light chain fragment of* D. melanogaster *(DNAL1 Dm) (A). The alignment of the amino acid sequences of dynein light chain fragments (DNAL1) of different organisms (*Danio rerio *– DANRE;* Xenopus laevis *– XENLA) and the LRR domain of SBR (NXF1 DROME) (B). Red letters denote identical amino acids; blue – identical amino acids in the dynein light chain and in the SBR. The bold type notes most often meeting amino acids in corresponding position in protein. Gray color notes interchangeable amino acids. Green color notes sequence of the LRR (leucine rich repeats) domain in SBR protein (http://www.uniprot.org/align/20*

During spermatid individualization, the dynein light chains 1 (DLC1) participate in the assembly of the F-actin [77]. Dynein is necessary for centrosome separation, for forming the division spindle, and for aligning chromosomes equatorially during metaphase [78, 79]. During the interaction with the surface of microtubules, dynein also interacts with MAP proteins [80]. During prometaphase, the DYNLT3 light chain can be observed in kinetochores. During metaphase, dynein moves toward the spindle pole [81, 82]. The dynein complex leaves the kinetochores along with checkpoint proteins. This could be related to the transport of checkpoint proteins (for example, Bub3) from kinetochores to spindle poles [83]. If we recall the homology of the proteins Bub3 and Rae1 [84] and the fact that the protein Rae1, found in RNP complexes that are important for forming the spindle, is capable of direct interaction with NXF1 [85], it is possible to consider these factors as polyfunctional. They are taking part both in nuclearcytoplasmic transport of macromolecules and in the formation of the mitotic

Because it is the light chain of dynein in the dynein complex that is responsible for interaction with the cargo [72], this resemblance to the N-terminus of the SBR protein suggests that SBR may have the same partners as a dynein complex (that these proteins can have the general partners or the general functions, and they are

*DOI: http://dx.doi.org/10.5772/intechopen.90917*

ing a similarity to the mutants of the *sbr* gene.

*Spermatogenesis in* Drosophila melanogaster: *Key Features and the Role of the NXF1… DOI: http://dx.doi.org/10.5772/intechopen.90917*

#### **Figure 6.**

*Animal Models in Medicine and Biology*

factors that interact with the plus-ends of microtubules.

where Tip stands for tyrosine kinase-interacting protein.

**source of evolutionary relationship**

this sequence are yet to be determined.

containing RNAs [74, 76].

+TIPs—complexes linked to the plus-ends of the microtubules—play a special role in the interaction of the plus-ends of the microtubules with the cell cortex [63]. +TIPs also play an important role in finding and capturing microtubule targets—the cortex and the chromosomes [64, 65]. Localized mRNAs are anchored at the plus ends of microtubules especially in polarized cells [66]. SBR also may be one of the

It is worth noting that the Hs NXF1 (TAP) factor in humans was initially identified *not* as a protein enabling transport of mRNA from the nucleus into the cytoplasm, but as a factor important for cellular adhesion and involved in cell signaling [67]. For this reason, the protein Hs NXF1 was called TAP—Tip-associated protein,

Tyrosine phosphorylation is important for regulating the assembly and disassembly of the actin cytoskeleton at cell-cell junctions. In many cases, tyrosine phosphorylation in proteins of the junction complex—plakoglobin and β-catenin in adherens junctions—disrupts interactions between cytoskeleton and membrane [68]. It is believed [61] that tyrosine phosphorylation in targets leads to the disassociation of phosphorylated actin from the contractile ring that forms during the cytokinesis of the cells comprising the syncytium during spermatogenesis. This stabilizes the interaction between the walls of the ring and the cell membrane, ends cell division, and forms the ring canal [61]. Building a new cell wall at the cleavage site during cytokinesis requires the involvement of components of the cell membrane and the signaling molecules [69]. A system of transport molecules ensures the delivery of the necessary elements to the region where the cell membrane is being formed [70]. Interactions of NXF1 with cytoskeleton [27] and the cellular membrane [67] may help finding partners of NXF1 in the cytoplasm. Not surprisingly, the closest evolutionary relative of NXF1 is dynein. Dynein plays a significant role in cytokinesis, chromosome segregation, and in enabling the movement of the flagellum of the

**6. Homology of proteins of the NXF family and axonemal dyneins as a** 

Searching for related proteins and aligning sequences using the multiple sequence alignment tool base has demonstrated that among the proteins that are homologous to the factor NXF1, axonemal dynein of various organisms—especially its light chain—is most frequent. Aligning sequences that exhibit homology demonstrates that the N-terminus of the Dm NXF1 protein, which includes RBD domains and the LRR (leucine-rich repeats), corresponds to the axonemal light chain of dynein in vertebrates (**Figure 6**). At the LRR site, there is a sequence that exhibits a high degree of homology (marked by bold typeface in **Figure 6**), both when comparing different NXF factors (orthologous and paralogous), and comparing the SBR protein with sequences of light chains of dynein (**Figure 6**). The functions of

The dynein complex is a multicomponent system consisting of light, light intermediate, intermediate, and heavy chains of dynein [72]. Interacting with a multitude of protein and ribonucleic partners, the LC8 and TcTex1 light chains of dynein enable a link between different forms of the transported cargo and heavy chains of dynein that function as molecular motors [73, 74]. By interacting with its partner dynacin complex, the dynein complex enables cytoplasmic transport of macromolecular complexes, vesicles, and organelles [75], including particles

**158**

sperm [70, 71].

*Results of the alignment of the amino acid sequences of LRR domains of different NXF factors, including SBR, and dynein light chain fragment of* D. melanogaster *(DNAL1 Dm) (A). The alignment of the amino acid sequences of dynein light chain fragments (DNAL1) of different organisms (*Danio rerio *– DANRE;* Xenopus laevis *– XENLA) and the LRR domain of SBR (NXF1 DROME) (B). Red letters denote identical amino acids; blue – identical amino acids in the dynein light chain and in the SBR. The bold type notes most often meeting amino acids in corresponding position in protein. Gray color notes interchangeable amino acids. Green color notes sequence of the LRR (leucine rich repeats) domain in SBR protein (http://www.uniprot.org/align/20 1202072EGVYDYGWG).*

In the fruit fly, the null mutants of the genes that encode the light or heavy chain of dynein have anomalies of wings and bristles, exhibit male and female sterility, and are characterized by disrupted sensory axon trajectories [71], thus demonstrating a similarity to the mutants of the *sbr* gene.

During spermatid individualization, the dynein light chains 1 (DLC1) participate in the assembly of the F-actin [77]. Dynein is necessary for centrosome separation, for forming the division spindle, and for aligning chromosomes equatorially during metaphase [78, 79]. During the interaction with the surface of microtubules, dynein also interacts with MAP proteins [80]. During prometaphase, the DYNLT3 light chain can be observed in kinetochores. During metaphase, dynein moves toward the spindle pole [81, 82]. The dynein complex leaves the kinetochores along with checkpoint proteins. This could be related to the transport of checkpoint proteins (for example, Bub3) from kinetochores to spindle poles [83]. If we recall the homology of the proteins Bub3 and Rae1 [84] and the fact that the protein Rae1, found in RNP complexes that are important for forming the spindle, is capable of direct interaction with NXF1 [85], it is possible to consider these factors as polyfunctional. They are taking part both in nuclearcytoplasmic transport of macromolecules and in the formation of the mitotic apparatus of the cell.

Because it is the light chain of dynein in the dynein complex that is responsible for interaction with the cargo [72], this resemblance to the N-terminus of the SBR protein suggests that SBR may have the same partners as a dynein complex (that these proteins can have the general partners or the general functions, and they are evolutionary conservative).
