The leptotene stage, also known as the leptonema, is the first of five substages of prophase I in

meiosis Meiosis (; , since it is a reductional division) is a special type of cell division of germ cells in sexually-reproducing organisms that produces the gametes, such as sperm or egg cells. It involves two rounds of division that ultimately resu ...

. The term ''leptonema'' derives from Greek words meaning "thin threads". A cell destined to become a

gamete A gamete (; , ultimately ) is a haploid cell that fuses with another haploid cell during fertilization in organisms that reproduce sexually. Gametes are an organism's reproductive cells, also referred to as sex cells. In species that produce t ...

enters the leptotene stage after its chromosomes are duplicated during

interphase Interphase is the portion of the cell cycle that is not accompanied by visible changes under the microscope, and includes the G1, S and G2 phases. During interphase, the cell grows (G1), replicates its DNA (S) and prepares for mitosis (G2). A c ...

. During the leptotene stage those duplicated chromosomes—each consisting of two

sister chromatids A sister chromatid refers to the identical copies (chromatids) formed by the DNA replication of a chromosome, with both copies joined together by a common centromere. In other words, a sister chromatid may also be said to be 'one-half' of the dup ...

—condense from diffuse

chromatin Chromatin is a complex of DNA and protein found in eukaryotic cells. The primary function is to package long DNA molecules into more compact, denser structures. This prevents the strands from becoming tangled and also plays important roles in r ...

into long, thin strands that are more visible within the

nucleoplasm The nucleoplasm, also known as karyoplasm, is the type of protoplasm that makes up the cell nucleus, the most prominent organelle of the eukaryotic cell. It is enclosed by the nuclear envelope, also known as the nuclear membrane. The nucleoplasm ...

. The next stage of prophase I in meiosis is the

zygotene Meiosis (; , since it is a reductional division) is a special type of cell division of germ cells in sexually-reproducing organisms that produces the gametes, such as sperm or egg cells. It involves two rounds of division that ultimately res ...

stage. During this stage, the chromosomes attach themselves by their ends (

telomere A telomere (; ) is a region of repetitive nucleotide sequences associated with specialized proteins at the ends of linear chromosomes. Although there are different architectures, telomeres, in a broad sense, are a widespread genetic feature mos ...

s) to the inner membrane of the nuclear envelope. At the transition to the zygotene stage the telomeres usually aggregate at a nuclear envelope sector, thereby forming a meiotic bouquet. Lateral (axial) elements of the synaptonemal complex are also formed. It is the first stage of Prophase 1 in Meiosis 1. Immediately after DNA damaging treatment ( gamma irradiation) during male mouse

, it is possible to distinguish two types of DNA repair response. From the leptotene stage to early pachytene, exogenous DNA damage triggers the massive presence of gammaH2AX throughout the

cell nucleus The cell nucleus (pl. nuclei; from Latin or , meaning ''kernel'' or ''seed'') is a membrane-bound organelle found in eukaryotic cells. Eukaryotic cells usually have a single nucleus, but a few cell types, such as mammalian red blood cells, h ...

, which is associated with

DNA repair DNA repair is a collection of processes by which a cell identifies and corrects damage to the DNA molecules that encode its genome. In human cells, both normal metabolic activities and environmental factors such as radiation can cause DNA dam ...

mediated by the

homologous recombination Homologous recombination is a type of genetic recombination in which genetic information is exchanged between two similar or identical molecules of double-stranded or single-stranded nucleic acids (usually DNA as in cellular organisms but may ...

proteins

DMC1 Meiotic recombination protein DMC1/LIM15 homolog is a protein that in humans is encoded by the ''DMC1'' gene. Meiotic recombination protein Dmc1 is a homolog of the bacterial strand exchange protein RecA. Dmc1 plays the central role in homologous ...

and RAD51. From mid-pachytene to diplotene the predominant DNA repair pathway is

non-homologous end joining Non-homologous end joining (NHEJ) is a pathway that repairs double-strand breaks in DNA. NHEJ is referred to as "non-homologous" because the break ends are directly ligated without the need for a homologous template, in contrast to homology direc ...

References

{{reflist Cellular processes

See also

References