Lampbrush chromosome

Detailed overview of lampbrush chromosomes

Lampbrush chromosomes are a special form of chromosome found in the oocytes of most animals, except mammals. They are characterized by their large size and distinctive appearance, which resembles a brush used for cleaning lamps, hence the name.

Structure

Lampbrush chromosomes are highly extended and transcriptionally active chromosomes. They are visible under a light microscope during the prophase of meiosis in the oocytes of amphibians, birds, and some other species. The chromosomes consist of a central axis with lateral loops extending outward. These loops are sites of active RNA synthesis.

The loops of lampbrush chromosomes are formed by chromatin fibers that are decondensed and extended. Each loop is a transcription unit, where RNA polymerase enzymes are actively transcribing DNA into RNA. This high level of transcription is necessary to produce the large amounts of RNA required for the development of the oocyte.

Function

The primary function of lampbrush chromosomes is to facilitate the rapid and massive production of RNA during oogenesis. The extended loops provide a large surface area for the assembly of the transcription machinery, allowing for efficient gene expression.

Lampbrush chromosomes also play a role in the storage and regulation of mRNAs and other RNA molecules that are crucial for early embryonic development. The RNAs synthesized on the loops are stored in the oocyte and used after fertilization to support the initial stages of embryogenesis.

Discovery and History

Lampbrush chromosomes were first observed in the late 19th century by Walther Flemming, but it was Oskar Hertwig who provided detailed descriptions and illustrations of these structures in 1906. The study of lampbrush chromosomes has contributed significantly to our understanding of chromosome structure and gene expression during meiosis.

Related pages

• Chromosome
• Meiosis
• Oogenesis
• RNA synthesis
• Gene expression

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  O. Hertwig 1906 Fig 5