Cell death in the central division of the medial preoptic nucleus of male and female lamb fetuses.
The medial preoptic area of the adult sheep contains an ovine sexually dimorphic nucleus (oSDN) that is larger and has more neurons in males than in females. In the lamb fetus, the nascent oSDN occupies the central division of the medial preoptic nucleus (MPNc) and consists of a cluster of cells that is organized by the action of testosterone during gestational days 60-90 of a 147 day term pregnancy. The current study sought to determine whether programmed cell death contributes to the emergence of the oSDN. Male and female lamb fetuses were euthanized at different ages spanning the period during which the oSDN is organized. The expression of the pro- and anti-apoptotic genes bcl-2 and bax, respectively, was measured by quantitative RT-PCR to assess possible sex differences in neuron vulnerability to programmed cell death. The appearance of DNA-fragmentation was detected by terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) and used to estimate the occurrence of apoptotic cell death. We found that bcl-2 and bax mRNA expression in the medial preoptic area of the developing lamb fetus decreased during the last half of the 147-day gestation. The ratio of bcl-2/bax gene expression was highest at gestational day 85 but was equivalent between males and females. TUNEL staining in the MPNc was very low and although it decreased significantly with age, it was not significantly different between sexes. These results using two different methods to assess cell death indicate that a sex difference in the incidence of cell death is not a primary mechanism leading to sexual differentiation of the oSDN.
Department of Physiology and Pharmacology, Oregon Health and Science University, 3181 SW Sam Jackson Park Road, Portland, OR 97239-3098, USA.
Radhika C
RC
Reddy
Department of Physiology and Pharmacology, Oregon Health and Science University, 3181 SW Sam Jackson Park Road, Portland, OR 97239-3098, USA.
Melissa
M
Scheldrup
Department of Animal and Rangeland Sciences, Oregon State University, Corvallis, OR 97331, USA.
Mary
M
Meaker
Department of Animal and Rangeland Sciences, Oregon State University, Corvallis, OR 97331, USA.
Fred
F
Stormshak
College of Veterinary Medicine, Oregon State University, Corvallis, OR 97331, USA.
Charles T
CT
Estill
Department of Physiology and Pharmacology, Oregon Health and Science University, 3181 SW Sam Jackson Park Road, Portland, OR 97239-3098, USA. Electronic address: rosellic@ohsu.edu.
Charles E
CE
Roselli
D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D053938:DNA Fragmentation; D005260:Female; D005333:Fetus; D018507:Gene Expression Regulation, Developmental / Q000502:physiology; D020287:In Situ Nick-End Labeling; D008297:Male; D009474:Neurons / Q000502:physiology*; D009929:Organ Size; D011301:Preoptic Area / Q000196:embryology* / Q000502:physiology*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012737:Sex Factors; D012756:Sheep; D051028:bcl-2-Associated X Protein / Q000378:metabolism*
D019253:Proto-Oncogene Proteins c-bcl-2; D012333:RNA, Messenger; D051028:bcl-2-Associated X Protein
Bax; Bcl2; Cell death; Fetus; Medial preoptic nucleus; Ovine sexually dimorphic nucleus; Sexual difference; Sexual differentiation; Sheep; TUNEL