Growth rates of follicles in the ovary of the cow

Abstract

Follicular growth rates were studied in 5 Hereford-Holstein cross heifers on Day 14 of the oestrous cycle. The granulosa cell mitotic index (MI) was measured in non-atretic antral follicles of various diameters (0.13-8.57 mm) from Bouin-fixed ovaries collected before (199, control) and 2 h after colchicine treatment (189, treated). In control ovaries, follicles of 0.68-1.52 mm had a higher MI than those of other size classes (P less than 0.05). In colchicine-treated ovaries, the MI of follicles ranging from 0.68 to 8.57 mm increased more than that of other sized follicles, so that the mitotic time was shorter (0.78 h vs 1.32 h) in medium and large sized follicles (0.68-8.57 mm) than in smaller follicles (0.13-0.67 mm). Calculations based on the number of granulosa cells in follicles of various classes and from the time required to double the number of cells within a follicle indicate that a follicle takes 27 days to grow from 0.13 to 0.67 mm, 6.8 days from 0.68 to 3.67 mm and 7.8 days from 3.68 to 8.56 mm, indicating that growth rates varied with the size of the follicle. A period equivalent to 2 oestrous cycles would therefore be required for a follicle to grow through the antral phase, i.e. from 0.13 mm to preovulatory size. Increased MI, decreased mitotic time and increased atresia found in follicles larger than 0.68 mm could indicate a change in the follicular metabolism during its maturation.

Characterization of microRNAs differentially expressed during bovine follicle development

“…Many of the signaling pathways overrepresented by these targets corresponded to growth factors putatively involved in follicular cell proliferation and steroidogenesis and prevention of premature luteinization including HGF, IGF1, TGFb, estrogen, neurotropin/TRK, PEDF, and NGF (Parrott et al 1993, Salas et al 2006, Glister et al 2010, Mani et al 2010, Garcia-Rudaz et al 2011, Chuderland et al 2013 and others involved in oocyte maturation including neuregulin, GDNF, and EGF (Conti et al 2006, Noma et al 2011, Linher-Melville & Li 2013, the fine-tune regulation of which is of key importance during the final stages of follicle development. Also present were several core cell cycle regulatory pathways (cell cycle regulation by BTG family proteins, estrogen-mediated S phase entry, and G1/S checkpoint regulation), a finding which is consistent with the notion that the development of the dominant follicle involves a substantial decrease in granulosa cell proliferation (Lussier et al 1987, Gaytan et al 1996. Bioinformatics analyses were complemented by demonstrating that the changes in the levels of selected transcripts during follicle development were consistent with these being the targets of miRNAs in large healthy follicles, specifically, a decrease in the expression of TGFBR2 and CREB1, two transcripts involved in TGFb and cAMP signaling and which are involved in follicular differentiation (Somers et al 1995, Wehrenberg et al 1998, and SPRED1 and ATG7, two transcripts involved in RAS/MAPK signaling and autophagy, respectively, and which expression during follicular development has not been previously characterized.…”

Role of transforming growth factor-β1 in gene expression and activity of estradiol and progesterone-generating enzymes in FSH-stimulated bovine granulosa cells

“…During this process, the proportion of follicles undergoing atresia increases dramatically with follicular diameter and the rate of atresia doubles between 2 and 8 mm (Lussier et al 1987). At the final growth phase, most follicles are atretic and only one follicle (exceptionally two) is selected to become dominant and continue to grow until ovulation (Fortune et al 2001).…”

Expression of protease nexin-1 and plasminogen activators during follicular growth and the periovulatory period in cattle

“…The growth of bovine follicles from the primordial to the preovulatory stage is characterized by the proliferation of cells and considerable increase in size of the follicle (Lussier et al 1987). The granulosa and theca cell layers are separated by the basal lamina, and the theca cells are enclosed in a dense extracellular matrix (ECM).…”