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Subzonal microinjection of mouse spermatozoa: insufficient sperm motility might induce phagocytosis
1Institute for Human Genetics, University of Göttingen, Federal Republic of Germany.
Abstract:
Acrosome-reacted CB6F1 mouse spermatozoa with slight flagellar motility were microinjected under the zona pellucida of CB6F1 mouse oocytes. Electron microscopy revealed the presence of swollen and decondensed sperm heads in the oocyte cytoplasm. Sixty-one percent of the microinjected oocytes reached a morphologically apparent two-cell stage, but chromosomal analysis demonstrated only haploid chromosomal complements in all cases. The exposure of microinjected oocytes to suspensions of spermatozoa of mice homozygous for a 2,4 reciprocal translocation resulted in normal fertilization and embryonic development with a maternally as well as a paternally derived haploid genome. Identical results were obtained with oocytes microinjected with medium and subjected to in vitro fertilization thereafter. Thus it can be suggested that the microinjected spermatozoa with insufficient flagellar motility are incorporated into the oocyte cytoplasm by phagocytosis. These spermatozoa do not induce a polyspermy block but induce the oocyte to parthenogenetic development.
Insights
Microinjected mouse sperm with low motility are phagocytosed by oocytes, leading to parthenogenetic development, not true fertilization. This process bypasses normal fertilization cues and results in haploid oocytes.
Area of Science:
- Reproductive Biology
- Developmental Biology
- Cell Biology
Background:
- Sperm-oocyte interactions are crucial for successful fertilization and embryonic development.
- Understanding the mechanisms of sperm incorporation and activation is key to reproductive research.
- Abnormal sperm function can lead to fertilization failure or developmental anomalies.
Purpose of the Study:
- To investigate the fate and effects of microinjected mouse spermatozoa with reduced motility into oocytes.
- To determine if such microinjected spermatozoa can induce normal fertilization and development.
- To elucidate the mechanism by which oocytes respond to these compromised spermatozoa.
Main Methods:
- Microinjection of acrosome-reacted CB6F1 mouse spermatozoa into CB6F1 mouse oocytes.
- Electron microscopy to examine sperm head decondensation within the oocyte.
- Chromosomal analysis of resulting embryos.
- In vitro fertilization (IVF) as a control.
Main Results:
- Microinjected spermatozoa decondensed within the oocyte cytoplasm.
- 61% of oocytes reached a two-cell stage, but all showed only haploid complements.
- Oocytes exposed to translocated sperm or IVF showed normal fertilization and development.
- Microinjected oocytes did not exhibit a polyspermy block.
Conclusions:
- Spermatozoa with insufficient motility are phagocytosed by oocytes.
- These incorporated spermatozoa do not trigger normal fertilization but induce oocyte parthenogenetic development.
- The oocyte's response is dependent on the sperm's ability to provide a diploid paternal genome and activate normal fertilization pathways.