Sexual Determination and Differentiation During Embryonic and Fetal Development of New Zealand Rabbit Females

Abstract

SUMMARY:The aim of this study was to know the embryonic and fetal development of the female rabbit genital system (Oryctolagus cuniculus), describing its main phases and the moment of sexual differentiation. Eleven pregnant New Zealand female rabbits were used in different gestational phases. The day of coitus was determined as day 0. For each stage a minimum of two animals was considered. The samples were obtained every two days from the ninth day post-coitus (dpc) until the 28 th dpc. The gestational period was divided in two: animals with undifferentiated sex (group 1) and animals with differentiated sex (group 2). The ages of embryos and fetuses were estimated through the crown-rump method. Subsequently, embryos and fetuses were dissected, fixed and processed to be embedded in paraffin (Histosec). The histological analysis was performed on sections stained with hematoxylin and eosin. Immunohistochemical analysis to determine sexual differentiation was performed on samples from the 16 th , 18 th and 28 th dpc. Desert Hedgehog (Dhh) and Indian Hedgehog (Ihh) primary antibodies, respectively, were used to identify cells of the male and female germinal epithelium. The immunohistochemical results showed that at the 16 th dpc, female sexual differentiation was evident, since positive expression of the Ihh protein was observed. Sexual differentiation was obtained through histological analysis on the 18 th dpc and through anatomical observation of the external genitalia on the 24 th dpc. Knowing the characteristics of the embryonic and fetal development of the female rabbit genital system as well as the moment of sexual differentiation make it possible to establish bases for future research that address the physiology and pathology of these organs. Thus, any alteration in the chain of events of sexual determination and differentiation must search for an explanation from the knowledge of the possible normal mechanisms affected.

Prenatal developmental study of the ovaries of the Baladi rabbits (oryctolagus cuniculus)

“…In this study, the ovarian differentiation of rabbit fetuses could be distinguished at 19 th day postconception while some investigators reported that it occurs at 16 th , 18 th days of fetal life in rabbit (Byskov et al, 1985;Duke, 1941;Mario et al, 2018). Moreover, the fetal ovaries of rabbit could be identified by absence of the primitive tunica albuginea and slight demarcation of the primitive parenchyma into an outer cortex and inner medulla.…”

“…The ovaries remained containing proliferating oogonia with no primordial follicles formation throughout the fetal life while the primordial follicles could be seen in the epithelium of the ovary at the 18 th days old rabbit fetus (Mario et al, 2018).…”

Becoming female: Ovarian differentiation from an evolutionary perspective

“…In rabbits, the gestation lasts 31 days and sex determination happens at 16 dpc. The bipotential gonads appear around 14 dpc ( Mario et al, 2018 ) ( Figure 1C ). The first event of somatic cell differentiation starts at 16 dpc ( Mario et al, 2018 ) and is associated with a regression of the mesonephros between 16 dpc to 25 dpc ( Bernier and Beaumont, 1964 ).…”

“…The bipotential gonads appear around 14 dpc ( Mario et al, 2018 ) ( Figure 1C ). The first event of somatic cell differentiation starts at 16 dpc ( Mario et al, 2018 ) and is associated with a regression of the mesonephros between 16 dpc to 25 dpc ( Bernier and Beaumont, 1964 ). Ovarian commitment is initiated at 18 dpc with the expression of FOXL2 , RSPO1 and WNT4 ( Daniel-Carlier et al, 2013 ).…”