**8.** *Trypanosoma brucei*

Human African trypanosomiasis (sleeping sickness) is caused by *T. brucei* infection (**Figure 3**). *T. brucei* undergoes meiosis within the salivary glands of its tsetse fly vector. Meiosis appears to be a normal part of the developmental cycle of *T. brucei* [49–51]. Three proteins that are only known to express during meiosis, Dmc1, Mad1 and Hop1, are found to be expressed in the nucleus of a small fraction of dividing epimastigote trypanosomes in the salivary glands and nowhere else [51, 52]. Haploid gametes produced by meiosis can subsequently undergo pairwise interaction leading to cell fusion [49].

**143**

**Figure 4.**

*(2N) nucleus [59].*

*Sexual Processes in Microbial Eukaryotes DOI: http://dx.doi.org/10.5772/intechopen.88469*

eukaryotes [49] (see Section 1).

**9.** *Neurospora crassa*

Tsetse flies are able to resist trypanosome infection by mounting immune defenses [50]. The flies' defenses include the ability to produce increased levels of reactive oxygen species (ROS) such as hydrogen peroxide [51, 53]. ROS can cause DNA damage, including double-strand breaks. *T. brucei* can carry out homologous recombinational repair of double-strand breaks [54]. Such a repair process is likely facilitated in *T. brucei* by homologous chromosome pairing during meiosis. This process may help

Trypanosomes are classified in the supergroup *Excavata* that are one of the earliest diverging eukaryotic lineages [55]. The discovery of a sexual stage in *T. brucei* supports the idea that meiotic sexual production is an ancestral characteristic of

The *Ascomycete Neurospora crassa* grows vegetatively as a haploid filamentous fungus. **Figure 4A** illustrates a segment of haploid hyphae which form a mass of

*(A)* Neurospora crassa *hyphae [58], (B)* Neurospora crassa *life cycle. The haploid mycelium reproduces asexually by two processes: (1) simple proliferation of existing mycelium, and (2) formation of conidia (macroand micro-) which can be dispersed and then germinate to produce new mycelium. In the sexual cycle, mating can only occur between individual strains of different mating type, A and a. Fertilization occurs by the passage of nuclei of conidia or mycelium of one mating type into the protoperithecia of the opposite mating type through the trichogyne. Fusion of the nuclei of opposite mating types occurs within the protoperithecium to form a zygote* 

protect *T. brucei* against the assault by ROS mounted by the tsetse fly host.

**Figure 3.** Trypanosoma brucei *[48].*

#### *Sexual Processes in Microbial Eukaryotes DOI: http://dx.doi.org/10.5772/intechopen.88469*

Tsetse flies are able to resist trypanosome infection by mounting immune defenses [50]. The flies' defenses include the ability to produce increased levels of reactive oxygen species (ROS) such as hydrogen peroxide [51, 53]. ROS can cause DNA damage, including double-strand breaks. *T. brucei* can carry out homologous recombinational repair of double-strand breaks [54]. Such a repair process is likely facilitated in *T. brucei* by homologous chromosome pairing during meiosis. This process may help protect *T. brucei* against the assault by ROS mounted by the tsetse fly host.

Trypanosomes are classified in the supergroup *Excavata* that are one of the earliest diverging eukaryotic lineages [55]. The discovery of a sexual stage in *T. brucei* supports the idea that meiotic sexual production is an ancestral characteristic of eukaryotes [49] (see Section 1).
