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Mechanisms of fertilization elucidated by gene-manipulated animals.

Okabe M - Asian J. Androl. (2015 Jul-Aug)

Bottom Line: These phenomena were found more than 60 years ago.However, fundamental questions regarding the nature of capacitation and the timing of the acrosome reaction remain unsolved.Factors were postulated over time, but as their roles were not verified by gene-disruption experiments, widely accepted notions concerning the mechanism of fertilization are facing modifications.

View Article: PubMed Central - PubMed

Affiliation: Center for Genetic Analysis for Biological Responses, Research Institute for Microbial Diseases, Osaka University, Yamadaoka 3-1, Suita, Osaka 565 0871, Japan.

ABSTRACT
Capacitation and the acrosome reaction are key phenomena in mammalian fertilization. These phenomena were found more than 60 years ago. However, fundamental questions regarding the nature of capacitation and the timing of the acrosome reaction remain unsolved. Factors were postulated over time, but as their roles were not verified by gene-disruption experiments, widely accepted notions concerning the mechanism of fertilization are facing modifications. Today, although in vitro fertilization systems remain our central research tool, the importance of in vivo observations must be revisited. Here, primarily focusing on our own research, I summarize how in vivo observations using gene-manipulated animals have elucidated new concepts in the mechanisms of fertilization.

No MeSH data available.


Related in: MedlinePlus

Fertilization requires two independent fusions. Intact spermatozoa have a plasma membrane (blue) and an acrosomal membrane (orange). After the acrosome reaction, these two membranes fuse and form a new sperm membrane (pink). The first fusion takes place between the pink membrane and egg plasma membrane (black). After the first fusion, egg and sperm membrane form a new consecutive membrane (green). If fusion is accomplished in this step, Izumo1 on the acrosomal cap of the inner acrosomal membrane (indicated by red) should spread on the newly-formed egg surface (green). However, the second fusion (invagination) follows the first fusion that separates the acrosomal cap and acrosomal sheath areas (light blue) from the fused membrane (green). Thus, Izumo1 on the inner acrosomal membrane is invaginated into the cytoplasm of the eggs. From live imaging, Izumo1 seems to be required for the first fusion. The nature of the second fusion remains totally unknown.
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Figure 3: Fertilization requires two independent fusions. Intact spermatozoa have a plasma membrane (blue) and an acrosomal membrane (orange). After the acrosome reaction, these two membranes fuse and form a new sperm membrane (pink). The first fusion takes place between the pink membrane and egg plasma membrane (black). After the first fusion, egg and sperm membrane form a new consecutive membrane (green). If fusion is accomplished in this step, Izumo1 on the acrosomal cap of the inner acrosomal membrane (indicated by red) should spread on the newly-formed egg surface (green). However, the second fusion (invagination) follows the first fusion that separates the acrosomal cap and acrosomal sheath areas (light blue) from the fused membrane (green). Thus, Izumo1 on the inner acrosomal membrane is invaginated into the cytoplasm of the eggs. From live imaging, Izumo1 seems to be required for the first fusion. The nature of the second fusion remains totally unknown.

Mentions: The dynamic movement of Izumo1 at fusion was also observed using the same transgenic mouse line. Izumo1 mainly localized to the equatorial segment dispersed in the first step of sperm-egg fusion. However, Izumo1 on the inner acrosomal membrane did not disperse but was incorporated into the cytoplasm of the egg, together with the inner acrosomal membrane structure. These Izumo1 movements were recorded in real time.52 In conjunction with electron microscopic observations reported by many researchers, we realized that the sperm-egg fusion is apparently divided into two different phases as explained in Figure 3.


Mechanisms of fertilization elucidated by gene-manipulated animals.

Okabe M - Asian J. Androl. (2015 Jul-Aug)

Fertilization requires two independent fusions. Intact spermatozoa have a plasma membrane (blue) and an acrosomal membrane (orange). After the acrosome reaction, these two membranes fuse and form a new sperm membrane (pink). The first fusion takes place between the pink membrane and egg plasma membrane (black). After the first fusion, egg and sperm membrane form a new consecutive membrane (green). If fusion is accomplished in this step, Izumo1 on the acrosomal cap of the inner acrosomal membrane (indicated by red) should spread on the newly-formed egg surface (green). However, the second fusion (invagination) follows the first fusion that separates the acrosomal cap and acrosomal sheath areas (light blue) from the fused membrane (green). Thus, Izumo1 on the inner acrosomal membrane is invaginated into the cytoplasm of the eggs. From live imaging, Izumo1 seems to be required for the first fusion. The nature of the second fusion remains totally unknown.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4492058&req=5

Figure 3: Fertilization requires two independent fusions. Intact spermatozoa have a plasma membrane (blue) and an acrosomal membrane (orange). After the acrosome reaction, these two membranes fuse and form a new sperm membrane (pink). The first fusion takes place between the pink membrane and egg plasma membrane (black). After the first fusion, egg and sperm membrane form a new consecutive membrane (green). If fusion is accomplished in this step, Izumo1 on the acrosomal cap of the inner acrosomal membrane (indicated by red) should spread on the newly-formed egg surface (green). However, the second fusion (invagination) follows the first fusion that separates the acrosomal cap and acrosomal sheath areas (light blue) from the fused membrane (green). Thus, Izumo1 on the inner acrosomal membrane is invaginated into the cytoplasm of the eggs. From live imaging, Izumo1 seems to be required for the first fusion. The nature of the second fusion remains totally unknown.
Mentions: The dynamic movement of Izumo1 at fusion was also observed using the same transgenic mouse line. Izumo1 mainly localized to the equatorial segment dispersed in the first step of sperm-egg fusion. However, Izumo1 on the inner acrosomal membrane did not disperse but was incorporated into the cytoplasm of the egg, together with the inner acrosomal membrane structure. These Izumo1 movements were recorded in real time.52 In conjunction with electron microscopic observations reported by many researchers, we realized that the sperm-egg fusion is apparently divided into two different phases as explained in Figure 3.

Bottom Line: These phenomena were found more than 60 years ago.However, fundamental questions regarding the nature of capacitation and the timing of the acrosome reaction remain unsolved.Factors were postulated over time, but as their roles were not verified by gene-disruption experiments, widely accepted notions concerning the mechanism of fertilization are facing modifications.

View Article: PubMed Central - PubMed

Affiliation: Center for Genetic Analysis for Biological Responses, Research Institute for Microbial Diseases, Osaka University, Yamadaoka 3-1, Suita, Osaka 565 0871, Japan.

ABSTRACT
Capacitation and the acrosome reaction are key phenomena in mammalian fertilization. These phenomena were found more than 60 years ago. However, fundamental questions regarding the nature of capacitation and the timing of the acrosome reaction remain unsolved. Factors were postulated over time, but as their roles were not verified by gene-disruption experiments, widely accepted notions concerning the mechanism of fertilization are facing modifications. Today, although in vitro fertilization systems remain our central research tool, the importance of in vivo observations must be revisited. Here, primarily focusing on our own research, I summarize how in vivo observations using gene-manipulated animals have elucidated new concepts in the mechanisms of fertilization.

No MeSH data available.


Related in: MedlinePlus