Aspects ultrastructuraux de la glande mammaire de lapine pendant la lactog�n�se

Bousquet, Marina; Fl�chon, J. E.; Denamur, R

doi:10.1007/bf00335217

Cited by 35 publications

(21 citation statements)

References 33 publications

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“…An alternative explanation is that proteins were degraded more rapidly during this period. This latter explanation is supported by the observation that the mammary gland undergoes some involution during this period, possibly caused by the unrelieved accumulation of milk [20].…”

Section: (A-a)supporting

confidence: 65%

Studies on the Synthesis of Casein Messenger RNA during Pregnancy in the Rabbit

Shuster

Houdebiné²,

Gaye³

1976

European Journal of Biochemistry

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The quantity of casein mRNA in the rabbit mammary gland was assayed during the course of pregnancy, by translation of casein mRNA in a reticulocyte lysate and by hybridization to DNA complementary to purified casein mRNA. Both methods indicated that the major increases in the concentration of casein mRNA in both polysomal and total cellular RNA occurred between the 18th and 25th day of pregnancy. The change in casein mRNA concentration during this period coincided with a sharp rise in casein synthesis in mammary gland explants suggesting that the levels of casein mRNA determine the rate of casein synthesis in the mammary gland.The sensitivity of the hybridization assay made it possible to detect the presence of casein mRNA in virgin animals and during the very early stages of pregnancy. At day 5, casein mRNA was found associated with polysomes indicating that there was probably some casein synthesis at this early stage of gestation. These results suggest that the hormones controlling lactogenesis in the rabbit may function by augmenting the rate of casein mRNA synthesis rather than initiating transcription of previously inactive genes.Previous studies on the growth of the mammary gland in pregnant rabbits have shown that significant increases in both wet weight and nucleic acid content occur between days 16 and 24 or pregnancy [I-51. It is also during this period that lactose synthetase activity is detected in the mammary gland and the synthesis and secretion of milk is first observed [5 -71.When considered in combination, these results suggested that the genes directing the synthesis of milk proteins were not actively transcribed until mid-pregnancy. At that time, they would presumably be switched on in response to a combination of the same hormonal influences which were responsible for the growth and maturation of the mammary gland [2,8 -111. In this report, we have tested this assumption by examining the content of casein mRNA in rabbit mammary gland during the entire course of pregnancy. We have used both the method of translation in a reticulocyte-lysate and hybridization to cDNA to assay for the presence of casein mRNA. In agreement with the results of recent experiments in the rat [12], we have found casein mRNA appearing in the rabbit mammary gland well before the onset of lactogenesis. Furthermore, the sensitivity of the hybridization technique has enabled us to detect casein mRNA in the mammary gland of virgin animals, indicating that there is a low level of transcription of casein genes in undeveloped tissue. We will present evidence that the casein mRNA detected in mammary glands during the first few days of pregnancy is found associated with a polysomal fraction indicating that it is translated even during the very early stages of gestation. MATERIALS AND METHODS AnimalsPrimiparous rabbits were used. The day of coitus was counted as day 0 of pregnancy. Animals were sacrified by exsanguination and the mammary glands were immediately excised and frozen at -30 "C. Four animals were used in each group...

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Section: (A-a)supporting

confidence: 65%

Studies on the Synthesis of Casein Messenger RNA during Pregnancy in the Rabbit

Shuster

Houdebiné²,

Gaye³

1976

European Journal of Biochemistry

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“…In the rat (Kuhn, 1968;McKenzie et al, 1971) and cow mammary gland, the appearance of lactose synthase activity, a-lactalbumin and lactose-biosynthetic capacity are temporally related during lactogenesis. In contrast, lactose synthase activity is present by midpregnancy in rabbit (present study) and mouse (McKenzie et al, 1971;Jones, 1972) (Bousquet et al, 1969) may be the last developmental step necessary for the acquisition of the capacity to synthesize lactose (Table 2) in the rabbit mammary gland pre partum.…”

Section: Discussioncontrasting

confidence: 52%

“…An increase in the concentration ofDNA and in the ratio of RNA/DNA also occurred (Table 1), which suggested an increase in protein synthesis by day 22 of pregnancy. Cellular maturation, as indicated by development of the endoplasmicreticulum and Golgi apparatus, is also accelerated between days 19 and 21 of pregnancy (Bousquet et al, 1969). In addition, the rate of synthesis of fatty acids increases at approximately day 21 of pregnancy in rabbit mammary tissue, and the pattern of lipids synthesized changes to that characteristic of rabbit milk lipids Mellenberger & Bauman, 1974).…”

Section: Discussionmentioning

confidence: 99%

“…However, there do not appear to have been any investigations with rabbit mammary tissue establishing the temporal relationships between lactose biosynthesis and the activity of relevant enzymes during pregnancy and lactation, although Denamur (1965) has reported the appearance of lactose in rabbit mammary tissue by day 22 of pregnancy. This would correspond to the first lactogenic stimulus given by fatty acid biosynthetic data Mellenberger & Bauman, 1974) and by cytological investigations (Bousquet et al, 1969). Since lactose is synthesized exclusively by the mammary gland and is closely related to total milk production (Wheelock & Rook, 1966), lactose biosynthesis would be indicative of the functional state of the mammary gland.…”

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confidence: 89%

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Metabolic adaptations during lactogenesis. Lactose synthesis in rabbit mammary tissue during pregnancy and lactation

Mellenberger

Bauman

1974

Biochemical Journal

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1. Mammary tissue, obtained from rabbits at various stages of pregnancy and lactation, was used for tissue-slice incubations to measure the rate of lactose biosynthesis and for relevant enzymic activity measurements. A biphasic adaptation in the rate of lactose synthesis and in the RNA concentration was noted during lactogenesis. 2. The first increase in the rate oflactose biosynthesis occurred between days 15 and 24 ofpregnancy. A second substantial increase was noted immediately postpartum. The overall rate of lactose biosynthesis increased 12-fold from day 24 of pregnancy to day 15 of lactation postpartum, and then decreased from 15 to 22 days post partum. 3. The RNA concentration/g wet wt. of tissue and the ratio of RNA/DNA closely represented the biphasic ability of the mammary-tissue slice to synthesize lactose. 4. Increases in the activities of UDP-glucose 4-epimerase (EC 5.1.3.2) and lactose synthase (EC 2.4

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“…The lumen of the acini contains granular and filamentous products. At days [14][15][16][17][18][19] of pregnancy or at 12-14 day of pseudopregnancy, the cytoplasm has a similar appearance but the lipid droplets are larger and more abundant and the lumen is filled with an homogenous electron-dense product [8]. In MEC from some rabbits, at this stage, a few casein micelles are detectable in the cytoplasm.…”

Section: Differentiation During Pregnancymentioning

confidence: 99%

Milk lipid and protein traffic in mammary epithelial cells: joint and independent pathways

Ollivier-Bousquet

2002

Reprod. Nutr. Dev.

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-In mammary epithelial cells, milk lipids and proteins are synthesised in the same compartment, the endoplasmic reticulum. Lipids, carried through the cytoplasm, associate with the apical membrane which then pinches off and releases the lipid globule. Proteins, carried through membrane compartments are released in the lumen after fusion of secretory vesicles with the apical membrane. These processes assure a relatively constant composition of milk but it is not known whether lipid and protein secretion are linked. The protein composition of the milk fat globule membrane and the stimulatory effects of prolactin and oxytocin on lipid and protein secretion suggest that these processes are coupled and co-regulated. However, it is possible to observe a dissociation between the formation and the secretion of the two constituents, during differentiation and in various experimental conditions, and this suggests that coupling is not strictly required. milk lipids / mammary epithelial cells / secretionRésumé -Transport des lipides et des protéines du lait dans les cellules épithéliales mammaires. Dans la cellule épithéliale mammaire, les lipides et les protéines du lait sont synthéti-sés dans le même compartiment, le reticulum endoplasmique. Les lipides transportés à travers le cytoplasme s'accolent à la membrane plasmique apicale qui les enveloppe avant leur sécrétion. Les protéines, transportées dans des compartiments membranaires jusqu'aux vésicules de sécrétion, sont libérées dans la lumière après fusion des vésicules avec la membrane apicale. Ces processus assurent une composition relativement constante du lait. Cependant, on ne sait pas si ces deux types de sécré-tion sont liés. La composition protéique de la membrane du globule gras et l'effet stimulant de la prolactine et de l'ocytocine sur la sécrétion des deux constituants suggèrent que synthèse et sécrétion sont liées et co-régulées. Cependant, la possibilité d'observer une dissociation entre la formation et la sécrétion des deux constituants suggère que ce couplage n'est pas obligatoire.lipides du lait / cellule épithéliale mammaire / sécrétion

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Aspects ultrastructuraux de la glande mammaire de lapine pendant la lactog�n�se

Cited by 35 publications

References 33 publications

Studies on the Synthesis of Casein Messenger RNA during Pregnancy in the Rabbit

Studies on the Synthesis of Casein Messenger RNA during Pregnancy in the Rabbit

Metabolic adaptations during lactogenesis. Lactose synthesis in rabbit mammary tissue during pregnancy and lactation

Milk lipid and protein traffic in mammary epithelial cells: joint and independent pathways

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