ABSTRACT
ABSTRACT The present review aims to summarize the research carried out in relation to meiosis in birds, especially by observing the protein axes of the chromosomes in prophase I of meiosis. This line of research, initially developed in Argentina, has provided key data in the study of the evolution of sex chromosomes and the mechanisms involved in the frequency and distribution of crossing over in birds, among other topics. Some of these contributions, in addition to those made by other authors, are described also providing the general theoretical framework or the hypotheses that support them.
RESUMEN La presente revisión tiene por objetivo resumir las investigaciones realizadas en relación a la meiosis de las aves, especialmente mediante la observación de los ejes proteicos de los cromosomas en la profase I de la meiosis. Esta línea de investigación, desarrollada inicialmente en Argentina, ha aportado datos clave dentro del estudio de la evolución de los cromosomas sexuales y los mecanismos involucrados en la frecuencia y distribución del crossing over en las aves, entre otros temas. Algunas de estas contribuciones, además de las realizadas por otros autores, se describen proporcionando también el marco teórico general o las hipótesis que las sustentan.
ABSTRACT
The synaptonemal complex (SC) is a meiosis-specific proteinaceous macromolecular structure that assembles between paired homologous chromosomes during meiosis in various eukaryotes. The SC has a highly conserved ultrastructure and plays critical roles in controlling multiple steps in meiotic recombination and crossover formation, ensuring accurate meiotic chromosome segregation. Recent studies in different organisms, facilitated by advances in super-resolution microscopy, have provided insights into the macromolecular structure of the SC, including the internal organization of the meiotic chromosome axis and SC central region, the regulatory pathways that control SC assembly and dynamics, and the biological functions exerted by the SC and its substructures. This review summarizes recent discoveries about how the SC is organized and regulated that help to explain the biological functions associated with this meiosis-specific structure.
Subject(s)
Animals , Chromosome Segregation , Meiosis/physiology , Synaptonemal Complex/physiologyABSTRACT
The structure, karyotype and behavior of synaptonemal complex (SC) in the spermatocytes of hedgehog (Erinaceus euroaaus dealbatus (insectivora)) were analyzed by light and electron microscopy with a modified surface spread preparation which involves the use of sodium dodecyl-sulphate (SDS) and silver staining. The lateral elements of the synaptonemal complex have a constant width of about 50 nm, the distance between the two lateral elements is about 100 nm. The relative length and arm rationale constant for each autosomal SC. The relative length and arm ratio constant for ea of the autosomal SCs are very similar to that of mitotic autosome.The X and Y chromosome axes have a clear morphological distinction from the autosomal SC. The axes of X and Y chromosome pair and form a SC of certain length at pachytene stage. The axes of unpaired X and Y chromosome are heteropycnotic and display various morphological complexities. But these differentiations in hedgehog are primary than in other mammalians, such as human and mice. At pachytene stage the X and Y chromosome display an extensive side-by-side pairing segment with decreasing length as meiotic prophase progressed.
ABSTRACT
Synaptonemal complex was first discovered by Moses in 1956. Synaptonemal complex of karyocytes of meiosis of pachytene are observed by electron microscope. They are bivalent chromosomal central substructure. We have observed synaptonemal complex of guinea-pig, rabbit, rat, and mice (Jin Bai Ⅰ, Ⅱ etc.). The basic structure of synaptonemal complex are similar. They contain two lateral elements and one central element which situated in the central space.The end of the synaptonemal complex is attached to the nuclear membrane,. where the inner nuclear membrane forms a thick platelike structure. Lateral elements of spermatocytes of the mouse are divided into two or three sections. The sex vesicle and associated nucleolus appear clearly in the mouse.The axial filaments of X and Y chromosome are attached with an angle of 30 degrees between each other. A typical central element and transverse filaments are formed in the space between. Several nodules are situated on the central element. The number of nodules is from 1-4 in the several experimental rodential animals studied.