Differences in the Kinetic of the First Meiotic Division and in Active Mitochondrial Distribution between Prepubertal and Adult Oocytes Mirror Differences in their Developmental Competence in a Sheep Model

Abstract

Our aim is to verify if oocyte developmental potential is related to the timing of meiotic progression and to mitochondrial distribution and activity using prepubertal and adult oocytes as models of low and high developmental capacity respectively. Prepubertal and adult oocytes were incorporated in an in vitro maturation system to determine meiotic and developmental competence and to assess at different time points kinetic of meiotic maturation, 2D protein electrophoresis patterns, ATP content and mitochondria distribution. Maturation and fertilization rates did not differ between prepubertal and adult oocytes (95.1% vs 96.7% and 66.73% vs 70.62% respectively for prepubertal and adult oocytes). Compared to adults, prepubertal oocytes showed higher parthenogenesis (17.38% vs 2.08% respectively in prepubertals and adults; P<0.01) and polispermy (14.30% vs 2.21% respectively in prepubertals and adults; P<0.01), lower cleavage rates (60.00% vs 67.08% respectively in prepubertals and adults; P<0.05) and blastocyst output (11.94% vs 34.% respectively in prepubertals and adults; P<0.01). Prepubertal oocytes reached MI stage 1 hr later than adults and this delay grows as the first meiotic division proceeds. Simultaneously, the protein pattern was altered since in prepubertal oocytes it fluctuates, dropping and rising to levels similar to adults only at 24 hrs. In prepubertal oocytes ATP rise is delayed and did not reach levels comparable to adult ones. CLSM observations revealed that at MII, in the majority of prepubertal oocytes, the active mitochondria are homogenously distributed, while in adults they are aggregated in big clusters. Our work demonstrates that mitochondria and their functional aggregation during maturation play an active role to provide energy in terms of ATP. The oocyte ATP content determines the timing of the meiotic cycle and the acquisition of developmental competence. Taken together our data suggest that oocytes with low developmental competence have a slowed down energetic metabolism which delays later development.

Delay in maternal transcript degradation in ovine embryos derived from low competence oocytes

“…The study was performed on a previously developed ovine model of differential developmental competence consisting of ovine oocytes derived from non‐hormonally treated adult and prepubertal donors. Similar models were previously analyzed in terms of morphology, metabolism and molecular status (Ledda et al, ; Leoni et al, , , ; Romar et al, ); in the present work, preliminarily to the molecular analysis, we confirmed the reduced developmental potential of prepubertal gametes in terms of in vitro developmental capabilities and kinetics. As expected, no differences were observed in terms of IVM, but both cleavage and blastocyst absolute rates and kinetics differed between the two groups of oocytes (Tables and ), with prepubertal embryos achieving lower rates in a longer time.…”

“…The efforts in identifying the reasons for the reduced developmental competence not only improved the rates of embryo production from prepubertal donors (Earl, Irvine, Kelly, Rowe, & Armstrong, ; Ledda et al, ), but interestingly shed light into numerous aspects involved in oocyte potential. Morphological, cellular, biochemical and molecular studies confirmed the differential competence of gametes derived from adult and prepubertal donors in terms of resistance to cryopreservation (Leoni et al, ), metabolism and ultrastructure (O'Brien, Dwarte, Ryan, Maxwell, & Evans, ), transcript abundance (Bebbere et al, ; Ledda et al, ; Leoni et al, ; Romar et al, ), in vitro developmental competence and kinetics (Landry et al, ; Leoni et al, , ; Majerus et al, ), mitochondrial distribution (Leoni et al, ) and methylation dynamics (Masala et al, ). Although the differential model has become a useful research tool independently on its breeding application, the limited competence of prepubertal oocytes is yet not fully understood.…”

Effects of melatonin on oocyte developmental competence and the role of melatonin receptor 1 in juvenile goats

“…Melatonin can also be beneficial for the IVEP using low quality oocytes like in the juvenile in vitro embryo transfer (JIVET). The developmental competence of oocytes from juvenile animals to develop to embryos is lower than those from adult animals (Leoni et al, ) due to the small size of the follicles from which they come (Romaguera et al, ) and their high ROS levels (Jiao et al, ). However, there is a great interest in improving JIVET for animal production as it reduces the generational interval and increases the genetic gain (Morton, ).…”

Transcriptome profile of one-month-old lambs’ granulosa cells after superstimulation

“…Furthermore, in vitro - adenosine triphosphate produced embryos derived from prepubertal oocytes show lower developmental rates [10]. The lower developmental competence maybe associated with deficiencies in the mRNA storage, incomplete nuclear maturation and adenosine triphosphate (ATP) content during oocyte growth [11–13]. It is well known that the oocytes and the GCs are in constant communication and the development of one influences the other’s compartment.…”