telomerase reverse transcriptase enzyme, primordial germ cells, transgenic, epididymal spermatozoa, Fluorescence in situ hybridization (FISH), pachytene, alternative pathway for telomere extension
Telomeres, replicated by telomerase, protect the ends of chromosomes from degradation and fusions that normal DNA replication cannot avoid. The regeneration of telomeres in mammals occurs in several phases throughout spermatogenesis and embryogenesis. During sperm formation, telomerase activity resides primarily in the á6+SP stem cells, and is most active during this early undifferentiated state of development, yet reach a maximum length during the elongated spermatid phase. The drop in telomerase activity during spermatogenesis is achieved by a decrease in TERT expression. Telomeres undergo further lengthening during embryogenesis, especially between the morula and blastocyst stages of development, where telomeres reach a predefined length regardless of initial length.
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