Spermatozoïde | EPFL Graph Search

vignette|Fécondation d'un ovule par un spermatozoïde humain. vignette|Spermatozoïdes de différents végétaux et algues : (1) Diatomée (2) Laminaire (3) Fucus (4) Marchantia (5) Plytrichum (mousse) (6) Lycopodium (7) Sélaginelle (8) Psilotum (9) Polypodium (10) Equisetum Un spermatozoïde est une cellule reproductrice (ou gamète) mâle mobile, intervenant dans la reproduction sexuée. Lors de la fécondation, le spermatozoïde s'unit à un ovocyte (gamète femelle) pour former une cellule-œuf, qui se développera ensuite en embryon pour donner un nouvel individu. Chaque spermatozoïde comprend un noyau, un système de locomotion (généralement un flagelle) et une vésicule nommée acrosome, riche en enzymes, qui lui permettront de pénétrer dans l'ovule. Le spermatozoïde est motile, il peut se déplacer par ses propres moyens, contrairement à l'ovule. Le spermatozoïde est une cellule haploïde, qui ne contient qu'un seul exemplaire de chaque chromosome. Son union ave

Mutations in the polyglutamylase geneTTLL5, expressed in photoreceptor cells and spermatozoa, are associated with cone-rod degeneration and reduced male fertility

Hereditary retinal degenerations encompass a group of genetic diseases characterized by extreme clinical variability. Following next-generation sequencing and autozygome-based screening of patients presenting with a peculiar, recessive form of cone-dominated retinopathy, we identified five homozygous variants [p.(Asp594fs), p.(Gln117*), p.(Met712fs), p.(Ile756Phe), and p.(Glu543Lys)] in the polyglutamylase-encoding gene TTLL5, in eight patients from six families. The two male patients carrying truncating TTLL5 variants also displayed a substantial reduction in sperm motility and infertility, whereas those carrying missense changes were fertile. Defects in this polyglutamylase in humans have recently been associated with cone photoreceptor dystrophy, while mouse models carrying truncating mutations in the same gene also display reduced fertility in male animals. We examined the expression levels of TTLL5 in various human tissues and determined that this gene has multiple viable isoforms, being highly expressed in testis and retina. In addition, antibodies against TTLL5 stained the basal body of photoreceptor cells in rat and the centrosome of the spermatozoon flagellum in humans, suggesting a common mechanism of action in these two cell types. Taken together, our data indicate that mutations in TTLL5 delineate a novel, allele-specific syndrome causing defects in two as yet pathogenically unrelated functions, reproduction and vision.

Oxford University Press2016

Mechanisms of differential centriole inheritance in C. elegans

Lukas von Tobel

Centrosomes are the principal microtubule organizing center (MTOC) of animal cells and comprise a pair of centrioles surrounded by pericentriolar material (PCM). Centriole number must be carefully regulated to ensure bipolar spindle formation and thus faithful chromosome segregation. In the germ line of most metazoan species, centrioles are maintained during spermatogenesis, but eliminated during oogenesis. Such differential behavior ensures that the appropriate number of centrioles is present in the newly fertilized zygote. In this doctoral thesis work, I describe our investigation of centriole elimination during oogenesis in C. elegans and I characterize sas-1, a factor important for maintaining centriole integrity, especially during spermatogenesis, to ensure that two centrioles are present in the zygote. Despite being a fundamental feature of sexual reproduction in metazoans, themechanisms governing centriole elimination during oogenesis are poorly understood. We investigate this question using antibodies directed against centriolar components and serial-section electron microscopy and we establish that centrioles are eliminated during the diplotene stage of the meiotic cell cycle. Moreover, we show that centriole elimination is compromised upon depletion of the helicase CGH-1. We also find that somatic cellsmake a minor contribution to this process, and demonstrate that the germcell karyotype is important for timely centriole elimination. These findings set the stage for a mechanistic dissection of centriole elimination in ametazoan organism. How centriole integrity is ensured after organelle assembly is poorly understood, including in sperm cells, where such integrity is particularly critical. In a genetic screen in C. elegans, sas-1 was identified as a locus important for the maintenance of centrioles in the early embryo. Our analysis reveals that sperm-derived sas-1 mutant centrioles lose their integrity shortly after fertilization, and that a related defect occurs when maternal sas-1 function is absent. We establish that sas-1 encodes a C2 domain containing protein that localizes to centrioles once they are assembled. Futhermore, we demonstrate that SAS-1 can bind and stabilize microtubules when expressed in human cells. We also identify C2CD3, a protein required for proper centriole formation, as a putative mammalian SAS-1 homolog. Together, we uncover an important component required for maintaining centrioles in sperm cells to ensure that two centrioles are present after fertilization and thus guarantee the continuity of the species.

EPFL2014

Mechanisms of differential centriole inheritance in C. elegans

Lukas von Tobel

EPFL2014