Welcome to The Visible Embryo
The Visible Embryo Birth Spiral Navigation
Fetal Timeline--- -Maternal Timeline-----News-----Prescription Drugs in Pregnancy---- Pregnancy Calculator----Female Reproductive System

WHO International Clinical Trials Registry Platform

The World Health Organization (WHO) has a Web site to help researchers, doctors and patients obtain information on clinical trials.

Now you can search all such registers to identify clinical trial research around the world!




Pregnancy Timeline

Prescription Drug Effects on Pregnancy

Pregnancy Calculator

Female Reproductive System


Disclaimer: The Visible Embryo web site is provided for your general information only. The information contained on this site should not be treated as a substitute for medical, legal or other professional advice. Neither is The Visible Embryo responsible or liable for the contents of any websites of third parties which are listed on this site.

Content protected under a Creative Commons License.
No dirivative works may be made or used for commercial purposes.


Pregnancy Timeline by SemestersDevelopmental TimelineFertilizationFirst TrimesterSecond TrimesterThird TrimesterFirst Thin Layer of Skin AppearsEnd of Embryonic PeriodEnd of Embryonic PeriodFemale Reproductive SystemBeginning Cerebral HemispheresA Four Chambered HeartFirst Detectable Brain WavesThe Appearance of SomitesBasic Brain Structure in PlaceHeartbeat can be detectedHeartbeat can be detectedFinger and toe prints appearFinger and toe prints appearFetal sexual organs visibleBrown fat surrounds lymphatic systemBone marrow starts making blood cellsBone marrow starts making blood cellsInner Ear Bones HardenSensory brain waves begin to activateSensory brain waves begin to activateFetal liver is producing blood cellsBrain convolutions beginBrain convolutions beginImmune system beginningWhite fat begins to be madeHead may position into pelvisWhite fat begins to be madePeriod of rapid brain growthFull TermHead may position into pelvisImmune system beginningLungs begin to produce surfactant
CLICK ON weeks 0 - 40 and follow along every 2 weeks of fetal development

Developmental biology - Puberty & Stem Cells

Sleeping Mammary Stem Cells Wake Up In Puberty

Researchers have discovered how the growth of milk-producing mammary glands is triggered during puberty...

Stem cells in the mammary gland remain quiet until stimulated to awaken by the protein FoxP1, according to new research from the Walter and Eliza Hall Institute published in the journal Developmental Cell.

The research expands our knowledge of how mammary glands - a component of the human breast - develop from stem cells. The discovery of FoxP1, underpins a new understanding of how defects in this process can lead to breast cancer. The research was led by Nai Yang Fu PhD, Professor Jane Visvader and Professor Geoff Lindeman, medical oncologist at the Royal Melbourne Hospital and Peter MacCallum Cancer Centre, in collaboration with Professor Gordon Smyth and his bioinformatics team.

Stem cells are cells that give rise to a wide range of cells types - yet often lie dormant in our body. Little is known about how these 'sleeping' cells wake into an active state until the discovery of the FoxP1 gene. This gene appears to trigger 'awakening' via the rapid growth and development of mammary glands. Without FoxP1, mammary stem cells remain locked in a dormant state and mammary glands do not grow.


According to Jane Visvader PhD, in puberty stem cells receive the order driving their rapid expansion. FoxP1 switches off the production of other cellular proteins by repressing those proteins' genes.

"A gene called FoxP1 is essential to making this signal happen in an adult. We discovered that FoxP1 switches off the production of one of the key proteins keeping mammary stem cells asleep. As the level of this protein drops, stem cells wake up and begin to divide, driving mammary gland growth," Dr Fu explains.
"This project brought together expertise in cell biology, developmental biology, bioinformatics and imaging to solve the question of how mammary stem cells wake up in puberty and affect breast tissue. We are still looking for the precise connections linking female hormones and FoxP1, but we are one step closer to understanding the detailed process of breast development. This is also helping us connect faulty cells that contribute to breast development with the development of breast cancer."

Jane E. Visvader PhD, Stem Cells and Cancer Division, The Walter and Eliza Hall Institute of Medical Research; Department of Medical Biology, The University of Melbourne, Parkville, Australia.

• Foxp1 is an essential transcription factor for mammary gland development
• Foxp1 controls the activation of quiescent MaSCs marked by Tspan8
• Foxp1 directly represses the transcription of Tspan8 in basal, but not luminal, cells
• Tspan8 deletion rescues the Foxp1-deficient mammary phenotype

Long-lived quiescent mammary stem cells (MaSCs) are presumed to coordinate the dramatic expansion of ductal epithelium that occurs through the different phases of postnatal development, but little is known about the molecular regulators that underpin their activation. We show that ablation of the transcription factor Foxp1 in the mammary gland profoundly impairs ductal morphogenesis, resulting in a rudimentary tree throughout life. Foxp1-deficient glands were highly enriched for quiescent Tspan8hi MaSCs, which failed to become activated even in competitive transplantation assays, thus highlighting a cell-intrinsic defect. Foxp1 deletion also resulted in aberrant expression of basal genes in luminal cells, inferring a role in cell-fate decisions. Notably, Foxp1 was uncovered as a direct repressor of Tspan8 in basal cells, and deletion of Tspan8 rescued the defects in ductal morphogenesis elicited by Foxp1 loss. Thus, a single transcriptional regulator Foxp1 can control the exit of MaSCs from dormancy to orchestrate differentiation and development.

Nai Yang Fu, Bhupinder Pal, Yunshun Chen, Felicity C. Jackling, Michael Milevskiy, François Vaillant, Bianca D. Capaldo, Fusheng Guo, Kevin H. Liu, Anne C. Rios, Nicholas Lim, Andrew J. Kueh, David M. Virshup, Marco J. Herold, Haley O. Tucker, Gordon K. Smyth, Geoffrey J. Lindeman and Jane E. Visvader.

About the Journal of Biological Chemistry
The research was supported by the Australian National Health and Medical Research Council, the Australian Cancer Research Foundation, Cure Cancer Australia, the National Breast Cancer Foundation, the Victorian Cancer Agency and the Victorian Government.

Return to top of page

Oct 26, 2018   Fetal Timeline   Maternal Timeline   News   News Archive

High resolution imaging of mammary gland ducts - was critical to the discovery of how
their growth is triggered in puberty. Credit: Walter and Eliza Hall Institute, Australia

Phospholid by Wikipedia