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Genetic approach to male meiotic division deficiency: the human macronuclear spermatozoa
1Laboratoire de Cytologie et Histologie, EA1533, UFR Biomédicale des Saints Pères, 45, Rue des Saints Pères, 75006 Paris, France. denise.escalier@biomedicale.univ-paris5.fr
Abstract:
Human macronuclear spermatozoa (also termed large-headed or macrocephalic spermatozoa) are tetraploid and represent a mammalian model of meiotic division deficiency (MDD). Their genetic origin is strongly suggested by the existence of familial cases. They arise from spermatocytes I with a blockage of organelle displacement at the pachytene stage which disables the assembly of a bipolar meiotic spindle. Spermiogenesis can sometimes be complete, showing that meiotic divisions and spermiogenesis can be decoupled. However, the microtubular manchette is unilateral leading to an irregular sperm nucleus. A severe MDD phenotype also exhibits atrophic flagella. Another MDD phenotype is characterized by arrest at the round spermatid stage, suggesting the existence of factors coordinating meiosis and spermatid differentiation. An attempt is made herein to understand why MDD spermatocytes escape the pachytene and spindle-assembly checkpoints. These human MDD are revisited in the light of Drosophila mutants for cell cycle factors, meiosis division-promoting factors and microtubule components. Several human genes are known to be homologous to genes involved in male MDD in Drosophila mutants, and their number will soon be increased. These candidate genes open the way to investigation of human genes possibly mutated in patients with macronuclear spermatozoa and/or macronuclear spermatids.
Insights
Human macronuclear spermatozoa, a model for meiotic division deficiency (MDD), arise from spermatocytes with blocked spindle assembly. Research explores genetic links by comparing human cases with Drosophila mutants.
Area of Science:
- Reproductive Biology
- Human Genetics
- Cell Biology
Background:
- Human macronuclear spermatozoa (large-headed or macrocephalic spermatozoa) are tetraploid cells representing a model for meiotic division deficiency (MDD).
- Familial cases suggest a genetic origin for MDD.
- MDD involves a blockage of organelle displacement at the pachytene stage, preventing bipolar meiotic spindle assembly.
Purpose of the Study:
- To investigate why MDD spermatocytes evade pachytene and spindle-assembly checkpoints.
- To explore the genetic underpinnings of human MDD by referencing Drosophila melanogaster mutants.
- To identify candidate human genes associated with macronuclear spermatozoa and/or spermatids.
Main Methods:
- Comparative analysis of human MDD phenotypes with Drosophila mutants affecting cell cycle, meiosis, and microtubule components.
- Review of existing literature on human macronuclear spermatozoa and related genetic factors.
- Identification of homologous genes between human MDD and Drosophila mutants.
Main Results:
- MDD can lead to incomplete spermiogenesis, unilateral microtubular manchette, irregular sperm nuclei, and atrophic flagella.
- Some MDD phenotypes show arrest at the round spermatid stage, indicating a need for coordinated meiosis and spermatid differentiation.
- Several human genes are homologous to those implicated in male MDD in Drosophila, with more expected.
Conclusions:
- Human MDD shares genetic parallels with Drosophila mutants, offering insights into meiotic errors.
- Identifying homologous genes provides a pathway for investigating genetic mutations in patients with macronuclear spermatozoa.
- Further research into these candidate genes is crucial for understanding the etiology of human MDD.