The LisH Domain-Containing N-Terminal Fragment is Important for the Localization, Dimerization, and Stability of Katnal2 in Tetrahymena

α- and β-tubulin C-terminal tails with distinct modifications are crucial for ciliary motility and assembly

α- and β-tubulin have an unstructured glutamate-rich region at their C-terminal tails (CTTs). The function of this region in cilia and flagella is still unclear, except that glutamates in CTTs act as the sites for post-translational modifications that affect ciliary motility. The unicellular alga Chlamydomonas possesses only two α-tubulin and two β-tubulin genes, each pair encoding an identical protein. This simple gene organization might enable a complete replacement of the wild-type tubulin with its mutated version. Here, using CRISPR/Cas9, we generated mutant strains expressing tubulins with modified CTTs. We found that the mutant strain in which four glutamate residues in the α-tubulin CTT had been replaced by alanine almost completely lacked polyglutamylated tubulin and displayed paralyzed cilia. In contrast, the mutant strain lacking the glutamate-rich region of the β-tubulin CTT assembled short cilia without the central apparatus. This phenotype is similar to mutant strains harboring a mutation in a subunit of katanin, the function of which has been shown to depend on the β-tubulin CTT. Therefore, our study reveals distinct and important roles of α- and β-tubulin CTTs in the formation and function of cilia.

Negative regulation of floral transition in Arabidopsis by HOS15-PWR-HDA9 complex

Arabidopsis HOS15/PWR/HDA9 repressor complex, which is similar to the TBL1/NcoR1/HDAC complex in animals, plays a well-known role in epigenetic regulation. PWR and HDA9 have been reported to interact with each other and modulate the flowering time by repressing AGL19 expression, whereas HOS15 and HDA9, together with the photoperiodic evening complex, regulate flowering time through repression of GI transcription. However, the role of the HOS15/PWR/HDA9 core repressor complex as a functional unit in the regulation of flowering time is yet to be explored. In this study, we reported that the loss-of-function hos15-2/pwr/hda9 triple mutant accumulates higher transcript levels of AGL19 and exhibits an early flowering phenotype similar to those of hos15, pwr, and hda9 single mutants. Interestingly, the accumulation of HOS15 in the nucleus was drastically reduced in pwr and hda9 mutants. As a result, HOS15 could not perform its role in histone deacetylation or interaction with H3 in the nucleus. Furthermore, HOS15 is also associated with the same region of the AGL19 promoter known for PWR-HDA9 binding. The acetylation level of the AGL19 promoter was increased in the hos15-2 mutant, similar to the pwr and hda9 mutants. Therefore, our findings reveal that the HOS15/PWR/HDA9 repressor complex deacetylates the promoter region of AGL19, thereby negatively regulating AGL19 transcription, which leads to early flowering in Arabidopsis.

Combinatorial and antagonistic effects of tubulin glutamylation and glycylation on katanin microtubule severing

Microtubules have spatiotemporally complex posttranslational modification patterns. How cells interpret this tubulin modification code is largely unknown. We show that C. elegans katanin, a microtubule severing AAA ATPase mutated in microcephaly and critical for cell division, axonal elongation, and cilia biogenesis, responds precisely, differentially, and combinatorially to three chemically distinct tubulin modifications-glycylation, glutamylation, and tyrosination-but is insensitive to acetylation. Glutamylation and glycylation are antagonistic rheostats with glycylation protecting microtubules from severing. Katanin exhibits graded and divergent responses to glutamylation on the α- and β-tubulin tails, and these act combinatorially. The katanin hexamer central pore constrains the polyglutamate chain patterns on β-tails recognized productively. Elements distal to the katanin AAA core sense α-tubulin tyrosination, and detyrosination downregulates severing. The multivalent microtubule recognition that enables katanin to read multiple tubulin modification inputs explains in vivo observations and illustrates how effectors can integrate tubulin code signals to produce diverse functional outcomes.

Knockout of Katnal2 Leads to Autism-like Behaviors and Developmental Delay in Zebrafish

KATNAL2 mutations have been associated with autism spectrum disorder (ASD) and other related neurodevelopmental disorders (NDDs) such as intellectual disability (ID) in several cohorts. KATNAL2 has been implicated in brain development, as it is required for ciliogenesis in Xenopus and is required for dendritic arborization in mice. However, a causative relationship between the disruption of Katnal2 function and behavioral defects has not been established. Here, we generated a katnal2 null allele in zebrafish using CRISPR/Cas9-mediated genome editing and carried out morphological and behavioral characterizations. We observed that katnal2^-/- embryos displayed delayed embryonic development especially during the convergence and extension (CE) movement. The hatched larvae showed reduced brain size and body length. In the behavioral tests, the katnal2^-/- zebrafish exhibited reduced locomotor activity both in larvae and adults; increased nocturnal waking activity in larvae; and enhanced anxiety-like behavior, impaired social interaction, and reduced social cohesion in adults. These findings indicate an important role for katnal2 in development and behavior, providing an in vivo model to study the mechanisms underlying the ASD related to KATNAL2 mutations.

The Mammalian Family of Katanin Microtubule-Severing Enzymes

The katanin family of microtubule-severing enzymes is critical for cytoskeletal rearrangements that affect key cellular processes like division, migration, signaling, and homeostasis. In humans, aberrant expression, or dysfunction of the katanins, is linked to developmental, proliferative, and neurodegenerative disorders. Here, we review current knowledge on the mammalian family of katanins, including an overview of evolutionary conservation, functional domain organization, and the mechanisms that regulate katanin activity. We assess the function of katanins in dividing and non-dividing cells and how their dysregulation promotes impaired ciliary signaling and defects in developmental programs (corticogenesis, gametogenesis, and neurodevelopment) and contributes to neurodegeneration and cancer. We conclude with perspectives on future katanin research that will advance our understanding of this exciting and dynamic class of disease-associated enzymes.

Biallelic mutations in KATNAL2 cause male infertility due to oligo-astheno-teratozoospermia

Oligo-astheno-teratozoospermia (OAT) is a common cause of male infertility, and most of idiopathic OAT patients are thought to be caused by genetic defects. Here, we recruited 38 primary infertile patients with the OAT phenotype and 40 adult men with proven fertility for genetic analysis and identified biallelic mutations of KATNAL2 by whole-exome sequencing in two cases. F013/II:1, from a consanguineous family, carried the KATNAL2 c.328C > T:p.Arg110X homozygous mutations. The other carried c.55A > G: p.Lys19Glu and c.169C > T: p Arg57Trp biallelic mutations. None of the KATNAL2 variants were found in the 40 adult men with proven fertility. The spermatozoa from patients with KATNAL2 biallelic mutations exhibited conspicuous defects in maturation, head morphology, and the structure of mitochondrial sheaths and flagella. KATNAL2 was mainly expressed in the pericentriolar material and mitochondrial sheath of the spermatozoa from control subjects, but it was undetectable in the spermatozoa from the patients. Furthermore, Katnal2 null male mice were infertile and displayed an OAT phenotype. Our results proved that the biallelic mutations in KATNAL2 cause male infertility and OAT in humans for the first time, to our knowledge, which could enrich the genetic defect spectrum of OAT and be beneficial for its accurate genetic screening and clinical diagnosis.