In the present study we have shown that the centriolar structures, which form the neck region of ... more In the present study we have shown that the centriolar structures, which form the neck region of the spermatid tail, can act as microtubule-organizing centers.
This is a summarizing review about some aspects of the morphogenesis and characteristics of mamma... more This is a summarizing review about some aspects of the morphogenesis and characteristics of mammalian spermatozoon. The morphology, biogenesis and function of the different spermatozoon structures are analysed, as well as different aspects, like immunology and endocrine control. Comparative morphology, fate and function of the male gamete during its passage through the epididymis and female tract are commented. The fact, that the phenomenon of spermiogenesis continues with the maturative changes in the epididymis, and that modifications occur in the female genital tract is put forward; this idea seems to be basic for understanding the role of many spermatozoon structures, as well as many biochemical and molecular changes that take place in the gamete. On the other hand, all these changes (spermiogenesis, maturation, capacitation and acrosomal reaction in the female tract), as well as the interaction sperm/egg are sequentially dependent, and are focussed on the sperming capacity of reaching and fertilizing the egg. Many gaps exist in regard to the functional role of different spermatozoon structures, and three important questions are emphasized with a view to solving these problems: a) The importance of the comparative analysis of spermatozoon and egg structures in different mammalian species. b) The necessity to develop ample studies using in vivo situations, particularly in reference to the changes occurred in the female tract. In this regard, the majority of studies have been developed in the in vitro situation, which is very different from the natural environment. c) The importance of using and compiling the different data (morphological, biochemical, molecular, etc.) about spermiogenesis, spermatozoon and fertilization. In the future, the use of new technologies appears as a promising idea to clarify doubts about spermatozoa biogenesis and function in mammals.
The structure of the zona pellucida (ZP) was analyzed in mouse oocytes collected soon after ovula... more The structure of the zona pellucida (ZP) was analyzed in mouse oocytes collected soon after ovulation and in others retrieved 20 h after. The conventional methods for electron microscopy and the alcoholic PTA staining procedure which preferentially contrasts lysine-rich proteins were employed. The ZP of aged oocytes showed several structural changes which were particularly observed after using the PTA procedure. In 82.14% of the aged oocytes the ZP appeared clearly composed of two different regions: an inner dense and an outer of low density. The ZP showed a fibrillar banded structure with a parallel arrangement of fibrillar threads in both the outer and inner regions. The in vitro fertilization analysis showed that only 16.85% of the aged gametes attained the two cell embryo stage in comparision to 66.93% shown by the freshly ovulated eggs. The non-fertilized oocytes showed that no sperm penetration through the ZP occurred.
Sperm maturation occurs in the mammalian spermatozoon during its passage through the epididymis. ... more Sperm maturation occurs in the mammalian spermatozoon during its passage through the epididymis. Maturation comprises a series of morpho-physiological changes, which includes the acquisition of the fertilizing capacity in the gamete. This maturative process has been particularly studied in mammals, but different data reveal that birds, reptiles and some kind of fish have a similar characteristic. Anatomical and histological analyses of mammalian epididymis and of Wolffian ducts of some birds and reptiles show the predominance of a secretory cell system. Proteins secreted by the male ducts seem to be an important factor involved in the acquisition of motility, as well as in the changes in the molecular organization of the plasma membrane. Changes occurring in the plasma membrane of the mammalian spermatozoon are related to the acquisition of foreign proteins (of epididymal origin). Some of these membrane changes seem to be connected with the capacitation phenomena and also with gamete interaction during fertilization. The use of antibodies against Wolffian duct proteins has shown that spermatozoa birds and reptiles also acquire proteins during their passage through the male duct. Nevertheless, in birds, and probably in reptiles, capacitation is not a pre-requisite for fertilization and some testicular spermatozoa are able to fertilize the egg. Then, what is the real significance of the membrane maturative changes in these subtherian vertebrates? Proteins acquired during maturation in such species must have different functions from those in mammals, to support spermatozoon survival and/or transport in the female tract, where spermatozoa are stored for a long time. Surface changes in mammals would possibly have similar roles when the gametes are in the female tract.
Summary A frequent coincidence of perinuclear microtubules and chromatin strands at nuclear membr... more Summary A frequent coincidence of perinuclear microtubules and chromatin strands at nuclear membrane level was observed in spermatids ofChorthippus apicalis andOedipoda coerulescens. More developed spermatids also show apparent continuity between these chromatin strands and microtubules. We would suggest the importance of this relationship in the arrangement adopted by these strands.
Spermiogenesis in mammals has been amply studied using conventional methods for electron microsco... more Spermiogenesis in mammals has been amply studied using conventional methods for electron microscopy (1). The ultrastructure of the neck region of spermatids has been analysed in some species (2) and appears formed by three main structures: the proximal centriole(PC), the distal centriole (DC) and the centriolar adjunct (CA) which is an extension of the PC composed by atypical triplets. All these microtubular (MT) structures have been specially analysed by means of conventional electron microscopy and only few analyses have been carried out using other methods, as cytochemical procedures, cell dissociation techniques,etc. For this reason in this communication the observations made on the neck structures after the application of cytochemical and dissociation procedures are reported. Moreover the observation of dissociated neck structures in spread and whole mount preparations has permited to apply the “in vitro” assembly of MT using purified MT proteins, thus testing the capacity of such structures to act as microtubule organizing centers (MTOC).
In microspores of Allium cepa , the nucleolus generally takes the form of two hemispherical masse... more In microspores of Allium cepa , the nucleolus generally takes the form of two hemispherical masses showing the same degree of development, consisting of the fibrillar and the granular components intermingled. The nucleolar organizing region (NOR) can be observed between the two nucleolar masses and is often in close connection with the masses of chromatin. It consists of a series of zones similar in density to the chromatin itself, arranged in a relatively orderly pattern in a region of low density. These dense zones consist of an accumulation of filaments measuring 100 A, while the less dense area consists of similar but less concentrated filaments connecting the dense zones with one another. Apparently it is this latter area which is in connection with the nucleolar masses. It may be supposed that in order to carry out its function the NOR assumes a pufflike structure.
The nucleoli of young spermatids of mice are described. They exhibit a very special shape resembl... more The nucleoli of young spermatids of mice are described. They exhibit a very special shape resembling a "padlock" in which three different areas can be distinguished: (a) a compact zone corresponding to the fibrillar component, (b) the granular component and (c) a fibrillar center of low density. Fibrillar and granular components usually appear segregated. This nucleolus has been reconstructed based on serial sectioning. When the silver impregnation technique is employed, both fibrillar and granular components show a positive reaction, although the fibrillar center is free of granules. The morphology of the fibrillar center seems to be similar to that reported in other cells. The possibility that these fibrillar centers correspond to the nucleolar organizer is discussed.
In the present study we have shown that the centriolar structures, which form the neck region of ... more In the present study we have shown that the centriolar structures, which form the neck region of the spermatid tail, can act as microtubule-organizing centers.
This is a summarizing review about some aspects of the morphogenesis and characteristics of mamma... more This is a summarizing review about some aspects of the morphogenesis and characteristics of mammalian spermatozoon. The morphology, biogenesis and function of the different spermatozoon structures are analysed, as well as different aspects, like immunology and endocrine control. Comparative morphology, fate and function of the male gamete during its passage through the epididymis and female tract are commented. The fact, that the phenomenon of spermiogenesis continues with the maturative changes in the epididymis, and that modifications occur in the female genital tract is put forward; this idea seems to be basic for understanding the role of many spermatozoon structures, as well as many biochemical and molecular changes that take place in the gamete. On the other hand, all these changes (spermiogenesis, maturation, capacitation and acrosomal reaction in the female tract), as well as the interaction sperm/egg are sequentially dependent, and are focussed on the sperming capacity of reaching and fertilizing the egg. Many gaps exist in regard to the functional role of different spermatozoon structures, and three important questions are emphasized with a view to solving these problems: a) The importance of the comparative analysis of spermatozoon and egg structures in different mammalian species. b) The necessity to develop ample studies using in vivo situations, particularly in reference to the changes occurred in the female tract. In this regard, the majority of studies have been developed in the in vitro situation, which is very different from the natural environment. c) The importance of using and compiling the different data (morphological, biochemical, molecular, etc.) about spermiogenesis, spermatozoon and fertilization. In the future, the use of new technologies appears as a promising idea to clarify doubts about spermatozoa biogenesis and function in mammals.
The structure of the zona pellucida (ZP) was analyzed in mouse oocytes collected soon after ovula... more The structure of the zona pellucida (ZP) was analyzed in mouse oocytes collected soon after ovulation and in others retrieved 20 h after. The conventional methods for electron microscopy and the alcoholic PTA staining procedure which preferentially contrasts lysine-rich proteins were employed. The ZP of aged oocytes showed several structural changes which were particularly observed after using the PTA procedure. In 82.14% of the aged oocytes the ZP appeared clearly composed of two different regions: an inner dense and an outer of low density. The ZP showed a fibrillar banded structure with a parallel arrangement of fibrillar threads in both the outer and inner regions. The in vitro fertilization analysis showed that only 16.85% of the aged gametes attained the two cell embryo stage in comparision to 66.93% shown by the freshly ovulated eggs. The non-fertilized oocytes showed that no sperm penetration through the ZP occurred.
Sperm maturation occurs in the mammalian spermatozoon during its passage through the epididymis. ... more Sperm maturation occurs in the mammalian spermatozoon during its passage through the epididymis. Maturation comprises a series of morpho-physiological changes, which includes the acquisition of the fertilizing capacity in the gamete. This maturative process has been particularly studied in mammals, but different data reveal that birds, reptiles and some kind of fish have a similar characteristic. Anatomical and histological analyses of mammalian epididymis and of Wolffian ducts of some birds and reptiles show the predominance of a secretory cell system. Proteins secreted by the male ducts seem to be an important factor involved in the acquisition of motility, as well as in the changes in the molecular organization of the plasma membrane. Changes occurring in the plasma membrane of the mammalian spermatozoon are related to the acquisition of foreign proteins (of epididymal origin). Some of these membrane changes seem to be connected with the capacitation phenomena and also with gamete interaction during fertilization. The use of antibodies against Wolffian duct proteins has shown that spermatozoa birds and reptiles also acquire proteins during their passage through the male duct. Nevertheless, in birds, and probably in reptiles, capacitation is not a pre-requisite for fertilization and some testicular spermatozoa are able to fertilize the egg. Then, what is the real significance of the membrane maturative changes in these subtherian vertebrates? Proteins acquired during maturation in such species must have different functions from those in mammals, to support spermatozoon survival and/or transport in the female tract, where spermatozoa are stored for a long time. Surface changes in mammals would possibly have similar roles when the gametes are in the female tract.
Summary A frequent coincidence of perinuclear microtubules and chromatin strands at nuclear membr... more Summary A frequent coincidence of perinuclear microtubules and chromatin strands at nuclear membrane level was observed in spermatids ofChorthippus apicalis andOedipoda coerulescens. More developed spermatids also show apparent continuity between these chromatin strands and microtubules. We would suggest the importance of this relationship in the arrangement adopted by these strands.
Spermiogenesis in mammals has been amply studied using conventional methods for electron microsco... more Spermiogenesis in mammals has been amply studied using conventional methods for electron microscopy (1). The ultrastructure of the neck region of spermatids has been analysed in some species (2) and appears formed by three main structures: the proximal centriole(PC), the distal centriole (DC) and the centriolar adjunct (CA) which is an extension of the PC composed by atypical triplets. All these microtubular (MT) structures have been specially analysed by means of conventional electron microscopy and only few analyses have been carried out using other methods, as cytochemical procedures, cell dissociation techniques,etc. For this reason in this communication the observations made on the neck structures after the application of cytochemical and dissociation procedures are reported. Moreover the observation of dissociated neck structures in spread and whole mount preparations has permited to apply the “in vitro” assembly of MT using purified MT proteins, thus testing the capacity of such structures to act as microtubule organizing centers (MTOC).
In microspores of Allium cepa , the nucleolus generally takes the form of two hemispherical masse... more In microspores of Allium cepa , the nucleolus generally takes the form of two hemispherical masses showing the same degree of development, consisting of the fibrillar and the granular components intermingled. The nucleolar organizing region (NOR) can be observed between the two nucleolar masses and is often in close connection with the masses of chromatin. It consists of a series of zones similar in density to the chromatin itself, arranged in a relatively orderly pattern in a region of low density. These dense zones consist of an accumulation of filaments measuring 100 A, while the less dense area consists of similar but less concentrated filaments connecting the dense zones with one another. Apparently it is this latter area which is in connection with the nucleolar masses. It may be supposed that in order to carry out its function the NOR assumes a pufflike structure.
The nucleoli of young spermatids of mice are described. They exhibit a very special shape resembl... more The nucleoli of young spermatids of mice are described. They exhibit a very special shape resembling a "padlock" in which three different areas can be distinguished: (a) a compact zone corresponding to the fibrillar component, (b) the granular component and (c) a fibrillar center of low density. Fibrillar and granular components usually appear segregated. This nucleolus has been reconstructed based on serial sectioning. When the silver impregnation technique is employed, both fibrillar and granular components show a positive reaction, although the fibrillar center is free of granules. The morphology of the fibrillar center seems to be similar to that reported in other cells. The possibility that these fibrillar centers correspond to the nucleolar organizer is discussed.
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