Ovary

H1FOO Is Coupled to the Initiation of Oocytic Growth

Abstract
We previously reported the discovery of a novel mammalian H1 linker histone termed H1FOO (formerly H1oo), a replacement H1 whose expression is restricted to the growing/maturing oocyte and to the zygote. The significance of this pre-embryonic H1 draws on its substantial orthologous conservation, singular structural attributes, selectivity for the germ cell lineage, prolonged nucleosomal residence and apparent predominance amongst germ cell H1s. Herein, we report that the intronic, single copy, five exon ( 5301bp) H1foo gene, maps to chromosome 6 and that the corresponding primary H1foo transcript gives rise to two distinct, alternatively spliced mRNA species (H1foo and H1foo) . The expression of the oocytic H1foo transcript and protein proved temporally coupled to the recruitment of resting primordial follicles into a developing primary follicular cohort and thus to the critical transition marking the onset of oocytic growth. The corresponding potential protein isoforms (H1FOO and H1FOO), both NLS-endowed but NES-free and possessing a significant net positive charge, localized primarily to peri-nucleolar heterochromatin in the oocytic germinal vesicle. Further investigation will be required to define the functional role of the H1FOO protein in the ordering of the chromatin of early mammalian development as well as its potential role in defining the primordial-to-primary follicle transition.

Key words: Meiosis • Oocyte development

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